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Blue tits do not return faster to the nest in response to either short- or long-term begging playbacks
Abstract
In species with parental care, offspring often solicit food through elaborate begging displays. Begging is thought to be a reflection of offspring need, but short-term fluctuations in begging do not necessarily provide reliable information. Parents thus have to adjust their provisioning behaviour to the changing demands of their offspring, while minimizing the costs of responding to unreliable information. We conducted two experiments with blue tits, Cyanistes caeruleus, in which we tested how parents respond to short-term and long-term changes in begging intensity. In the first experiment we investigated how parents respond to increased begging during a single nest visit. In the second experiment we investigated how parents respond to increased begging during every nest visit for 1 h. Parents did not return faster to the nest during the short-term manipulation. Contrary to our expectations, however, parents also did not return faster to the nest in response to long-term manipulation. Instead, parents spent more time in the nestbox during both the short-term and the long-term manipulation. Our results highlight that the general pattern of a positive parental response to increased begging may not be a universal one. Comparisons across species and populations may help reveal the factors underlying variation in parental responsiveness to begging.
... This method will overestimate visit number whenever individuals stay in the nestbox longer than 30 s and underestimate visit number whenever individuals perform more than one visit in 30 s. Note that during periods of peak feeding activity, the latter occurs for less than 8% of visits (Santema et al. 2017, Iserbyt et al. 2018. Second, we used the light barrier information to establish the most likely action of the bird when the transponder was read: flying in, flying out, at the entrance hole while staying outside of the box or at the entrance hole while inside the box. ...
... We used transponder data to extract visits to the active nestbox as described above and considered each visit by a parent during the nestling period as a feeding event (Santema et al. 2017). Broods of monogamous males were only included from 2012 onwards, because higher data quality in later years reduced the work required for compilation. ...
Classic explanations for polygyny consider habitat, genetic makeup and paternal care, but little attention has been paid to social inertia. We studied facultative social polygyny in a population of Blue Tits Cyanistes caeruleus with a low rate of polygyny (3% of males across 12 years). Occurrence of polygyny was best predicted by social turnover after the disappearance of one or more individuals; habitat quality and individual phenotypic traits were unimportant. Females settled as secondary females with a male and in an area they had previously associated with, indicating a role of familiarity in the formation of polygyny. Females mated to polygynous males received less help feeding nestlings. Reduced paternal care is potentially costly, because these females survived less well than females mated to monogamous males. Reduction in care occurred at both primary and secondary nests although polygynous males rarely divided their care between nests. On any given day during the nestling period, polygynous males were more likely than monogamous males to not feed nestlings at all and – as a consequence – polygynous males provided less care in total than monogamous males. Polygynous males rarely intermingled visits at both nests, suggesting a cost of switching between feeding locations. Both primary and secondary nests had reduced fledging success, even after controlling for variation in habitat quality and paternal care, due to a higher rate of nest failure. Paternity loss was higher at secondary nests, presumably because the secondary female copulated with a previous mate that disappeared. Due to increased paternity loss and reduced fledging success polygynous males did not sire more fledglings than monogamous males in a given season. Thus, the benefit of social polygyny for males seems limited. Social polygyny in our population probably arises as a by-product of widowed females settling as secondary mates with a familiar male or in a familiar area, thereby making the best of a bad situation.
... We estimated the number of visits made to each nestbox by an individual other that the social parents as the number of readings of the focal individual's ID that were more than 30 s apart. This method provides a good estimate of visit rates, as nest visits in blue tits rarely last more than 30 s during the peak provisioning period and two separate visits are rarely less than 30 s apart (Santema et al. 2017, Iserbyt et al. 2018. ...
... We considered individuals that visited a nest more than 100 times during the nestling period as those that contributed to offspring care. This is the equivalent of about five hours of continuous feeding by a social parent during the peak provisioning period (Santema et al. 2017). ...
Most birds are socially monogamous with both parents providing offspring care, but sometimes individuals are observed to provision at a nest that is not their own. One possible explanation for this behaviour is that it is a fitness maximising strategy by males who have copulated with the female and hence potentially sired extra‐pair offspring in the focal nest. Over a period of 8 years and among a total of 854 nests, we observed 12 blue tits Cyanistes caeruleus that provisioned at a nest that was not their own. In all cases, the provisioning individual was a male who had no nestlings of its own, either because its breeding attempt had failed (n = 5), because it was a non‐breeder (n = 6) or because the eggs in its own nest had not hatched yet (n = 1). Only two out of the 12 males had sired offspring in the nest where they helped, but most others had had interactions with the female during her presumed fertile period or were close neighbours, and hence may have performed extra‐pair copulations that did not result in fertilisations. In 10 out of the 12 cases, the resident male was not present anymore, either because it had disappeared (n = 7) or because it was socially polygynous and provided care at its other, primary nest (n = 3). Our findings suggest that females can benefit from extra‐pair copulations by obtaining help in raising their brood when they do not receive help from their social mate. Extra‐pair copulations could thus function as an ‘insurance' strategy with a relatively small cost.
... Data generated by individuals with visit rates beyond this threshold are characterized by "x" in both panels. Panel b represents data validation for the proportion of alternated (red dots) and synchronized (blue squares) visits in the nest box: 8-15 s; time spent between visits: 40-100 sec; Santema et al., 2017). The cutoff time may further be applicable for great tits as well, since average time spent in the nest box is less than 30 s in >90% of all great tit visits (Wilkin et al., 2009) and the time between visits peaks around 90 s (Johnstone et al., 2014;Schlicht, Santema, Schlicht, & Kempenaers, 2016). ...
... Based on these trimmed readings, we calculated behavioral activity for each ID as the number of nest arrivals per hour (i.e., nest visit rate). Nest visit rate is frequently interpreted as an estimate for parental investment during the nestling phase(Royle et al., 2012; for blue tits:Santema, Schlicht, Schlicht, & Kempenaers, 2017;Lucass, Fresneau, et al., 2016;Lucass, Iserbyt, et al., 2016). We then sorted the trimmed readings chronologically to calculate the level of coordinated provisioning within a pair(Johnstone et al., 2014). ...
Automated animal monitoring via radio‐frequency identification (RFID) technology allows efficient and extensive data sampling of individual activity levels and is therefore commonly used for ecological research. However, processing RFID data is still a largely unresolved problem, which potentially leads to inaccurate estimates for behavioral activity. One of the major challenges during data processing is to isolate independent behavioral actions from a set of superfluous, nonindependent detections. As a case study, individual blue tits (Cyanistes caeruleus) were simultaneously monitored during reproduction with both video recordings and RFID technology. We demonstrated how RFID data can be processed based on the time spent in‐ and outside a nest box. We then validated the number and timing of nest visits obtained from the processed RFID dataset by calibration against video recordings. The video observations revealed a limited overlap between the time spent in‐ and outside the nest box, with the least overlap at 23 s for both sexes. We then isolated exact arrival times from redundant RFID registrations by erasing all successive registrations within 23 s after the preceding registration. After aligning the processed RFID data with the corresponding video recordings, we observed a high accuracy in three behavioral estimates of parental care (individual nest visit rates, within‐pair alternation and synchronization of nest visits). We provide a clear guideline for future studies that aim to implement RFID technology in their research. We argue that our suggested RFID data processing procedure improves the precision of behavioral estimates, despite some inevitable drawbacks inherent to the technology. Our method is useful, not only for other cavity breeding birds, but for a wide range of (in)vertebrate species that are large enough to be fitted with a tag and that regularly pass near or through a fixed antenna.
... A single nest visit typically involves multiple transponder readings because the parent has to enter the nestbox and leave the nestbox and sometimes lands more than once at the entrance hole or stays at the hole for some time before entering the nestbox. Previous work on blue tits showed that the duration of a nest visit during the peak provisioning period is typically less than 30 s and that the interval between the separate nest visits is typically more than 30 s (Iserbyt et al., 2018;Santema et al., 2017). We, therefore, defined a nest visit as a transponder reading that was more than 30 s after the previous reading from the same individual. ...
In many animal species, including most birds, parental care is performed by both parents, which has important implications for mate choice (good parent hypothesis) and parental investment strategies. Partitioning the variance in measures of parental care into heritable and non-heritable components is important to understand the evolvability of parental investment and its potential role in mate choice. We employed an automated system to monitor provisioning behavior at 817 blue tit nests over 10 years (totaling ~3 million visits). Daily provisioning rates of males and females were moderately repeatable between years (Radj = 0.16 and 0.15 respectively), which was almost entirely explained by additive genetic effects. While this degree of heritability is sufficient for parental investment to respond to selection, we argue that the modest level of repeatability provides limited potential for a ‘provisioning phenotype’ to be used as a criterion in mate choice. Daily visit rates were positively correlated between pair members, but after accounting for shared environmental factors this relationship became clearly negative, thereby providing support for models of partial compensation. Visit rates also differed substantially between years, and between days within a year. Thus, it is important to account for these variables when comparing parental investment between individuals. Our results highlight the interplay between genetic, social, and environmental influences on provisioning behavior.
... Previous work has shown that overall, partial compensation is how parents react to a change in their partners' effort 7 . However, matching responses were also found 7,11 , and have been tested to explain their occurrence and stability 8,9,45 . Turn taking, as a strategy to resolve conflict, is a strategy which allows parents to match each other's investment. ...
Sexual conflict arises when two individuals invest in their common offspring because both individuals benefit when their partner invests more. Conditional cooperation is a theoretical concept that could resolve this conflict. Here, parents are thought to motivate each other to contribute to provisioning visits by following the rules of turn taking, which results in equal and efficient investment. However, parents have other tasks besides provisioning, which might hinder taking turns. To investigate restrictions by other care tasks and whether turn taking can be used to match investment, we manipulated brooding duration in female blue tits (Cyanistes caeruleus) during the early nestling phase by changing nest box temperature. As expected, females subjected to cold conditions brooded longer than females under warm conditions. Yet, contrary to our prediction, females had similar visit rates in both treatments, which suggests that females in the cold treatment invested more overall. In addition, the females’ turn taking level was higher in the more demanding cold condition (and the calculated randomised turn taking levels of females did not differ), hence females don’t seem to be restricted in their turn taking strategy by other care tasks. However, males did not seem to match the females’ turn taking levels because they did not adjust their visit rates. Thus, level of turn taking was not restricted by an other sex-specific task in females and did not facilitate a greater investment by their male partners.
... For each parent, we quantified the number of nest visits/h during each presentation day as the number of readings that were more than 30 s apart from the previous reading of the same parent. This method provides a reliable estimate of visit rates, as nest visits in blue tits rarely last more than 30 s during the peak provisioning period and two separate visits are rarely less than 30 s apart (Santema et al. 2017;Iserbyt et al. 2018). ...
Leaving the nest is a key transition in the life of altricial birds, whereby fledging decisions should depend on multiple factors, including the risk of predation. High postfledging predation risk may favour fledging at a more advanced stage of development, if more developed fledglings are better at escaping predation, or together with others. While comparative studies have highlighted the role of predation risk for between-species variation in the timing of fledging, drivers of within-species variation in fledging behaviour remain largely unknown. We presented owl models near blue tit, Cyanistes caeruleus, nests during the first half of the day throughout the fledging period to simulate an increased risk of postfledging predation. Using an automated monitoring system, we then recorded the precise fledging times of 595 nestlings from 105 nests (52 predator-treated, 53 control nests). Contrary to our predictions, the predator presentations did not affect the age at which nestlings fledged, the time of day of fledging or other aspects of fledging behaviour. The tendency to fledge together with siblings was affected, but the effect was in the opposite direction to that expected, with nestlings exposed to the predator treatment being more likely to fledge alone. Parents visited predator-treated nests less often, but this effect diminished over the course of the morning. We suggest several explanations for why the behavioural responses to the predation risk manipulation were generally limited.
... PIT tags are lightweight, inexpensive and require no battery power, enabling large-scale deployment over long periods of time, and they can be used in both laboratory (Boogert, Farine, & Spencer, 2014;Farine, Spencer, & Boogert, 2015;Griffith, Holleley, Mariette, Pryke, & Svedin, 2010;Weissbrod et al., 2013) and field conditions (Adelman, Moyers, Farine, & Hawley, 2015;Aplin et al., 2015;Bonter & Bridge, 2011;Broderick & Godley, 1999;Farine, Aplin, Garroway, Mann, & Sheldon, 2014;König et al., 2015;Mariette et al., 2011;Steinmeyer, Mueller, & Kempenaers, 2013). Although many individuals can be tagged, the antennas can only detect one individual at a time and only at fixed focal locations, such as nest boxes (Santema, Schlicht, Schlicht, & Kempenaers, 2017;Schlicht, Valcu, & Kempenaers, 2015), feeders (Firth, Sheldon, & Farine, 2016), or puzzle-boxes , which limits resolution for assessing interactions among individuals. ...
The study of animal behavior is a fundamental pursuit for answering scientific questions across a variety of fields — including neuroscience, psychology, ecology, genetics, and evolution. While the task of collecting accurate and complete behavioral data has typically always been difficult, laborious, and subjective, in recent years there has been rapid progress in methods for automatically quantifying behavior objectively and at scale. This progress has been primarily driven by the emergence of new computational hardware, software, and algorithms for measuring behavior. In order to reveal core insights about how animals organize their behavior with the increased quality and resolution of these data comes the need for new methods for data- driven modeling. Here, in this thesis, I focus on computational tools—the development of new algorithms and software—for measuring and modeling behavior using methods from computer vision, deep learning, Bayesian inference, and probabilistic programming, while also synthesizing these approaches with ideas from other relevant areas such as information theory, nonlinear dynamics, and statistical physics. First, I developed a barcode tracking system for automated behavioral studies where the location and identity of individuals can be reliably tracked over several weeks (or potentially longer) using conventional computer vision (Chapter 1). Next, I developed general-purpose deep learning methods for measuring animal posture — any set of user-selected body parts — in the laboratory and field (Chapter 2). Finally, I introduce methods for using these posture data to model behavior with techniques from machine learning and Bayesian statistical inference (Chapter 3). Together these methods reduce barriers to measuring and modeling animal behavior and allow researchers to answer scientific questions that were previously intractable.
... We also used these data to estimate the hourly number of visits made by each parent as the number of readings that were more than 30 s apart from the previous reading of the same parent. This method provides a reliable estimate of visit rates, as nest visits in blue tits rarely last more than 30 s during the peak provisioning period and two separate visits are rarely less than 30 s apart (Santema, Schlicht, Schlicht, & Kempenaers, 2017;Iserbyt, Griffioen, Borremans, Eens, & Müller, 2018). ...
In altricial birds, leaving the nest is a key life history transition associated with a high risk of mortality. Studies of numerous species have shown that young typically fledge early in the day, and it is often asserted that early fledging is important for survival; however, evidence for this hypothesis is limited. We used an automated monitoring system to obtain precise fledging times of 1582 young blue tits, Cyanistes caeruleus, from 230 nests. As expected, nestlings primarily fledged early in the day (84% fledged before midday). However, we found no evidence that early fledging was associated with higher postfledging survival (i.e. recorded the following autumn or later). We propose two alternative explanations for the morning peak in fledging. Hypothesis 1 is that some offspring reach a developmental threshold for fledging overnight and leave the nest early the next day. This is supported by our observation that offspring that fledged early in the day tended to be more developed than those that fledged later in the day, that is, they were older and had a high body mass (measured at 14 days of age) for their fledging age. Hypothesis 2 is that the timing of fledging is related to parental provisioning behaviour. Our results do not support this hypothesis. Parents reduced their nest visit rate over the course of the day, but offspring did not fledge earlier when their parents decreased their visit rate more strongly with time of day. In conclusion, our results do not support the notion that the time of fledging affects survival but suggest a link with nestling development.
... PIT tags are lightweight, inexpensive and require no battery power, enabling large-scale deployment over long periods of time, and they can be used in both laboratory (Boogert, Farine, & Spencer, 2014;Farine, Spencer, & Boogert, 2015;Griffith, Holleley, Mariette, Pryke, & Svedin, 2010;Weissbrod et al., 2013) and field conditions (Adelman, Moyers, Farine, & Hawley, 2015;Aplin et al., 2015;Bonter & Bridge, 2011;Broderick & Godley, 1999;Farine, Aplin, Garroway, Mann, & Sheldon, 2014;König et al., 2015;Mariette et al., 2011;Steinmeyer, Mueller, & Kempenaers, 2013). Although many individuals can be tagged, the antennas can only detect one individual at a time and only at fixed focal locations, such as nest boxes (Santema, Schlicht, Schlicht, & Kempenaers, 2017;Schlicht, Valcu, & Kempenaers, 2015), feeders (Firth, Sheldon, & Farine, 2016), or puzzle-boxes , which limits resolution for assessing interactions among individuals. ...
1. Recent advances in technology allow researchers to automate the measurement of animal behaviour. These methods have multiple advantages over direct observations and manual data input as they reduce bias related to human perception and fatigue, and deliver more extensive and complete data sets that enhance statistical power. One major challenge that automation can overcome is the observation of many individuals at once, enabling whole-group or whole-population tracking.
2. We provide a detailed description for implementing an automated system for tracking birds. Our system uses printed, machine-readable codes mounted on backpacks. This simple, yet robust, tagging system can be used simultaneously on multiple individuals to provide data on bird identity, position and directionality. Further, because our codes and backpacks are printed on paper, they are very lightweight.
3. We describe the implementation of this automated system on two flocks of zebra finches. We test different camera options, and describe their advantages and disadvantages. We show that our method is reliable, relatively easy to implement and monitor, and with proper handling, has proved to be safe for the birds over long periods of time. Further, we highlight how using single-board computers to control the frequency and duration of image capture makes this system affordable, flexible, and adaptable to a range of study systems.
4. The ability to automate the measurement of individual positions has the potential to significantly increase the power of both observational and experimental studies. The system can capture both detailed interactions (using video recordings) and repeated observations (e.g. once per second for the entire day) of individuals over long timescales (months or potentially years). This approach opens the door to tracking life-long relationships among individuals, while also capturing fine-scale differences in behaviour.
... Experimental manipulations of parental behavior may be more effective approaches than analyzing observational provisioning data to investigate the existence of turn-taking. Manipulations could involve brood size (Baldan et al., 2019;Griffioen et al., 2019a), begging playback at the nest (Santema et al., 2017) or handicapping of one of the parents (Griffioen et al., 2019b). In particular, manipulations directed at only one parent (e.g., selective playback or handicapping) can be used to investigate whether parents do, indeed, react to the provisioning behavior of their mate. ...
How parents negotiate over parental care is a central issue in evolutionary biology because it affects the evolutionary outcome of sexual conflict. A recent theoretical model shows that “turn-taking” in provisioning visits by the parents can be an evolutionarily stable negotiation strategy, and empirical studies have shown that parental nest-visits do indeed alternate more than expected by chance. However, such alternation may also be generated by a refractory period, or by correlated temporal heterogeneity (CTH) in provisioning rates of the two parents driven by temporal environmental variation. Here we use a recently developed measure of alternation and a novel measure of CTH in the provisioning rates of pairs to clarify what can be concluded about the occurrence of turn-taking from the provisioning patterns of pairs. First, we show using a simulation model that turn-taking can, by itself, generate both a refractory period and CTH in provisioning rates. Second, we incorporate this insight into a conceptual framework that combines an existing randomization analysis with a novel analytical approach in which “pseudo-pairs” are created by analytically pairing the provisioning sequence of a parent at one nest with the contemporaneous provisioning sequence of the other-sex parent at a nearby nest. This allows us to partition the alternation score into different components. This approach confirms that isolating a component of alternation that can be unequivocally attributed to turn-taking is probably impossible. However, the pseudo-pairs analysis does isolate a component that can be unequivocally attributed to general temporal environmental variation [environmental variation that causes CTH in provisioning rates across (as well as within) pairs]. Third, we use these techniques to partition the alternation score of 17 pairs of great tits Parus major provisioning in the wild. Approximately 8% of the observed alternation score is due to the frequency distribution of the inter-visit intervals, 74% to nest-specific effects on the sequence of inter-visit intervals, and 18% to general effects on the sequence of inter-visit intervals. This last component can be unequivocally attributed to general temporal environmental variation, and is the first empirical demonstration of alternation by free-living provisioning parents being generated by temporal environmental variation.
... Even the existence of active turn-taking during parental care remains contentious, as the analysis methods and null models used by prior empirical studies leave open the possibility that the observed turn-taking is a result of environmental influences that drive correlated changes in parental visit rate on the scale of individual care events (Ihle et al., 2019;Santema et al., 2019). Future studies should carefully manipulate short-term parental investment (Santema et al., 2017), the ability to monitor partner investment (Iserbyt et al., 2015), or cost asymmetries within pairs (Firth et al., 2015) to create a more complete picture of the degree to which parents respond to each other, under what contexts, and at what temporal scale. ...
Sexual conflict is inescapable when two parents care for offspring, because providing care is personally costly, while the benefits of successful reproduction are shared. Previous models that treat parental investment as a continuous trait, with stable levels of effort negotiated between parents over evolutionary or behavioral time, generally predict that sexual conflict will lead to under-investment in the young, as each parent stands to gain by leaving its partner to bear a greater share of the costs of care. More recently, a model of parental investment as repeated discrete contributions suggested that a more efficient outcome can be reached through parents adopting a simple strategy of conditional cooperation by “turn-taking”: only investing after each contribution by their partner. However, while empirical work suggests that parental visits are significantly alternated in a number of natural systems, all examples thus far exhibit imperfect turn-taking rather than the strict rule predicted by theory. To help bridge this gap, we here present a more realistic mathematical model of parental turn-taking, incorporating (i) errors in parents' ability to monitor the contributions of their partner, (ii) time-dependent costs and benefits of delivering care, (iii) differences between partners in payoffs (and consequently in behavior), (iv) differences between partners in the accuracy with which they can monitor one another's behavior, and (v) shared costs of care. We illustrate how the degree of conditional cooperation is influenced by each of these factors, and discuss ways in which our model could be tested empirically.
... When individuals deliver discrete, relatively brief care events to offspring (e.g., provisioning, defense), care/visit rates or the mean and variance of carer inter-visit intervals (IVIs) are useful metrics to quantify behavior. Most literally, IVIs refer to the periods between an individual leaving a nest or den and its next arrival (Santema et al., 2017), but IVIs are also commonly characterized as the time between consecutive arrivals (e.g., Johnstone et al., 2014); for clarity we refer to this latter case as the inter-arrival interval (IAI). When discrete care events are somewhat longer (e.g., nest maintenance) it can also be informative to characterize the within (or intra-) visit intervals (WVI) of carers. ...
In many species, individuals must contribute extensively to offspring care to reproduce successfully. Within species, variation in care is driven by local social, physiological, and environmental contexts, and this relationship has been a major focus of behavioral ecology since the inception of the field. The majority of existing studies on care, both theoretical and empirical, have focused on measuring the amount of care delivered by each carer as a proxy for individual investment, linking this investment to the local context, and investigating outcomes for offspring. However, more recently interest has grown in the finer-scale details of care, including how individuals respond to each other's behavior, and temporal variation in care both within and between stages. Simultaneously, advances in remote monitoring methods, such as video cameras and passive integrated transponder (PIT) tag systems, have vastly increased the ease of collecting large amounts of care data, providing opportunities to study carer behavior in much greater detail than previously possible. In this mini-review we provide an overview of the dimensions of carer behavior that can be quantified, illustrated using recent studies from a variety of taxa. We classify these analyses into three broad groups: (a) how parental care is distributed in time, (b) variation within care events, and (c) how carers interact when jointly providing care. Our aim is to encourage more in-depth analyses of parental care, to build a more complete picture of how animals rear their offspring.
... As explained extensively in Schlicht et al. (2016), Ihle et al. (2019), and Santema et al. (2019), both pair members might have correlated patterns of interfeeding intervals due to experiencing the same environmental conditions, which could lead to a pattern of apparently coordinated visits to the nest. Teasing apart environmentally induced patterns of alternation and synchrony from patterns of true coordination emerging from conditional cooperation will not be possible without measuring all environmental parameters (which is in itself probably impossible) or conducting logistically challenging experiments (e.g., Santema et al., 2017). It will therefore be crucial in further studies of pair coordination to explore fitness consequences, instead of solely showing that alternation or synchrony is higher than expected by chance. ...
In species with biparental care, behavioral coordination in the provisioning of the progeny is hypothesized to increase the number of offspring that survive to independence. Coordination is often quantified by two metrics, alternation and synchrony. Turn-taking (leading to an alternation pattern) can result when one parent's investment strategy is based on the investment of its partner (i.e., conditional cooperation). This should increase the overall provisioning rate and improve offspring body condition. Synchrony might equalize food delivery among offspring and therefore decrease the variance in offspring body condition within the brood. Overall, offspring survival could be increased by parental coordination. Finally, pairs with low coordination, and with potentially lower reproductive success, are expected to be more likely to divorce. In this study, we use a dataset on 473 pairs of house sparrows in a natural insular population to test these hypotheses. We found no effect of the pair's apparent coordination on offspring condition, offspring survival, or divorce rate, questioning the adaptive significance of this behavior. We argue that, in this species, the detection of a higher frequency of alternation and synchrony, when compared to chance expectation, might be induced by the environment, rather than result from an emergent pair behavior selected for fitness benefits.
... However, our experiment does not enable us to independently assess the effects of brood size per se and partner activity in parental provisioning rules. Experiments with simultaneous manipulation of brood size and provisioning rate of one parent, for example by handicapping or playback (Santema, Schlicht, Schlicht, & Kempenaers, 2017), might be a reasonable approach to shed light on the behavioural mechanisms underlying provisioning rules. ...
In species with biparental care, the amount of care devoted to offspring is affected by the negotiation rules that the parents adopt. Recently, turn taking in provisioning visits has been proposed as a negotiation rule by which parents respond to their partner's behaviour, which results in a perfect alternation of the nest visits by the parents. Empirical evidence suggests that parents do not strictly alternate their visits, and, so far, this imperfect alternation has received no experimental investigation. In this study, we tested whether alternation of nest visits might be subject to time constraints affecting the ability of parents to strictly take turns. We manipulated the workload of 15 great tit, Parus major, pairs using a short-term brood size manipulation. Parental nest visits alternated more in reduced than control and enlarged broods. To understand whether this variability could be caused by changes in turn taking, we explored the rate and regularity of the parents' intervisit intervals. Treatment differences in alternation were still present when controlling for the rate and regularity of the visits by each of the two parents, suggesting that workload also affected alternation via the temporal sequence of the intervals (e.g. via turn taking). Our results show that alternation of nest visits varies in response to workload and is not merely a by-product of variation in visit rate or regularity.
... Few studies explicitly investigated the time span of nestling begging to which parents respond, but most studies suggest that parents respond relatively quickly to changes in nestling need, even on a visit-by-visit basis (e.g., Wright and Leonard 2002;McDonald et al. 2009a have used begging intensity (as we measured it) as the main cue for increasing provisioning effort. Indeed, several studies suggest that parents can or should ignore begging under certain ecological conditions (Davis et al. 1999;Thorogood et al. 2011;Caro et al. 2016) and begging playback experiments suggest they do (Santema et al. 2017). Parents might use other decision rules, for example, monitoring their long-term food delivery and compensating for temporary shortfalls regardless of begging. ...
Parental provisioning behavior is a major determinant of offspring growth and survival, but high provisioning rates might come at the cost of increased predation threat. Parents should thus adjust provisioning activity according to current predation threat levels. Moreover, life-history theory predicts that response to predation threat should be correlated with investment in current reproduction. We experimentally manipulated perceived predation threat in free-living great tits (Parus major) by presenting parents with a nest predator model while monitoring different aspects of provisioning behavior and nestling begging. Experiments were conducted in 2 years differing greatly in ecological conditions, including food availability. We further quantified male territorial aggressiveness and male and female exploratory tendency. Parents adjusted provisioning according to current levels of threat in an apparently adaptive way. They delayed nest visits during periods of elevated perceived predation threat and subsequently compensated for lost feeding opportunities by increasing provisioning once the immediate threat had diminished. Nestling begging increased after elevated levels of predation threat, but returned to baseline levels by the end of the experiment, suggesting that parents had fully compensated for lost feeding opportunities. There was no evidence for a link between male exploration behavior or aggressiveness and provisioning behavior. In contrast, fast-exploring females provisioned at higher rates, but only in the year with poor environmental conditions, which might indicate a greater willingness to invest in current reproduction in general. Future work should assess whether these personality-related differences in delivery rates under harsher conditions came at a cost of reduced residual reproductive value.
... A meta-analysis revealed that partial compensation is the general parental response in mate handicapping or mate removal studies (Harrison et al., 2009). However, manipulation of one or both parents can also result in no response (Schwagmeyer, Mock & Parker, 2002;Santema et al., 2017) and even a matching response (Hinde, 2006;Meade et al., 2011). Such variation in parental responses may in part stem from multitude of applied methods and may even be observed within the same study. ...
Recent studies have proposed that conditional cooperation may resolve sexual conflict over the amount of care provided by each parent. Such conditional cooperation may allow parents to equalize their investment by alternating their provisioning visits. This alternated pattern of male and female visits, that is, alternation, is thought to stimulate each other's investment leading to higher levels of provisioning and potential benefits for offspring development. However, experimental studies testing the role of alternation as an adaptive parental strategy to negotiate the level of investment are still absent. Therefore, we manipulated blue tit (Cyanistes caeruleus) parents by temporarily changing their brood sizes to induce changes in demand and thus visit rates. Parents were expected to visit more-assuming that prey sizes were constant-and alternate at higher levels when confronted with an enlarged brood given the greater potential for sexual conflict. In contrast, in reduced broods visit rates and alternation may become lower due to the smaller investment that is needed for reduced broods. We show that the level of alternation did not differ in response to the manipulated brood sizes, despite a directional change in visit rates for enlarged and reduced broods as expected. Nestlings did not benefit from high levels of alternation as no effects on nestling mass gain were present in either of the different manipulations. These findings indicate that alternation does not serve as a mechanism to motivate each other to feed at higher rates. Parents hence appeared to be inflexible in their level of alternation. We therefore suggest that the level of alternation might reflect a fixed agreement about the relative investment by each of the caring parents.
... Such between nest effect would, of course, be weakened the more environmental variables are shared within pairs but not between pairs, for instance because they occur on a small geographic scale (e.g., presence of a predator). Alternatively, logistically challenging experiments would be needed, where one individual is manipulated to return faster to the nest (e.g., by selectively playing back begging calls or providing food) and the return rate of its partner examined (Santema et al., 2017) or where one parent's provisioning rate is kept hidden from its partner whose subsequent behavior is then analyzed (Iserbyt et al., 2015). More experimental work with ingenious designs are require to test the conditional cooperation hypothesis and whether pair coordination is an adaptive emergent behavior. ...
Behavioral coordination when provisioning offspring, through alternation and synchrony, has been hypothesized to influence rearing success. However, studying coordination at the pair level presents two analytical difficulties. First, alternating or synchronous (i.e., simultaneous) feeding can occur randomly and be induced by a shared environment. Therefore, a null model must account for this apparent coordination that occurs by chance. Second, alternation and synchrony in provisioning are intrinsically linked to the rate of provisioning itself, and the effects of coordination and provisioning rate, for instance on fitness, need to be distinguished. In this paper, we explore several randomization procedures and simulation scenarios to tease apart true coordination from random alternation and synchrony, and to find an appropriate statistical model for analyzing coordination. First, to establish a baseline of alternated or synchronous visits expected by chance, we took data from a natural population of house sparrows and randomized inter-feeding intervals in various ways. Alternation and synchrony in the observed dataset were higher than expected by chance under any of our randomizations. However, it was impossible to exclude that alternation and synchrony patterns did not arise due to the pair's shared environment. Second, to identify a way of statistically modeling coordination without generating spurious effects due to intrinsic mathematical relationships between coordination and provisioning rates, we simulated data according to different scenarios. Only one out of five candidate models for analyzing alternation was deemed appropriate, and gave similarly appropriate results for analyzing synchrony. This work highlights the importance and difficulty of finding an adequate null model for studying behavioral coordination and other emergent behaviors. In addition, it demonstrates that analyzing simulated data, prior to analyzing empirical data, enables researchers to avoid spurious effects.
... In such experiments, however, care should be taken that the hunger level of the offspring is not affected by the treatment, because this would influence the behavior of the parents and confound the interpretation of the results. This may be achieved by manipulating provisioning effort on the scale of single nest visits, e.g., by playing back extra begging calls to a parent during a single nest visit to reduce its subsequent inter-visit interval (Santema et al., 2017). The prediction would be that a faster return to the nest by the manipulated parent should lead to a faster return to the nest by the other, unmanipulated, parent. ...
... In addition, nestlings can reduce the begging loudness (volume) and increase the frequency (pitch) of vocalization in areas with high predation rates, making it more difficult for the predators to find the nest ( Briskie et al., 1999). An increase in nestling begging volume and frequency, as well as by playback from speakers, normally increases parental feeding rate as intended (Bengtsson & Rydén, 1983;Hinde & Kilner, 2007;Tarwater et al., 2009), but not always ( Santema et al., 2017). The drawback is often that higher parental activity seems to increase nest predation rate (Martin et al., 2000b;Badyaev & Ghalambor, 2001;Muchai & du Plessis, 2005). ...
Despite nest predation being the most common cause of breeding failure in open-nesting birds, we have little insight into the cues used by nest predators when they search for nests. So far we have assumed that nest-predating birds are visually oriented while mammal predators to a large extent use scent and auditory cues like nestling begging calls. To evaluate how important nestling begging calls are for corvid nest predators searching for nests, I used artificial nests, which made it possible to find the real costs of the begging without mitigation by parental and nestling behavior. I used paired artificial nests, one with and one without nestling begging call playback. Within 10 days, 62.9% of the nests were predated. The analyses showed that nests with begging calls suffered a significantly higher predation rate than nests without begging calls, especially when the nests were placed close to corvid nests. Moreover, nests with begging calls were predated significantly earlier than nests without begging calls. In artificial nest pairs with both nests predated but on different days, nests with begging calls were predated first. In nest pairs with only one predated nest, nests with begging calls were predated most often. This experiment shows that nestling begging calls imply a cost in terms of increased and earlier nest predation, and that corvids use nestling begging calls as a cue to find and depredate bird nests, challenging earlier expectations.
... Removal of these two males did not change the results.We assessed the time of day at which individuals disappeared by extracting for each individual the time of day when it was last recorded at the nest. As blue tits visit their nest at high rates during the nestling period, with intervals between visits typically not more than a few minutes (see, e.g.Santema, Schlicht, Schlicht, & Kempenaers, 2017), the time of their last visit to the nest provides an accurate estimate of the time of disappearance from the population. For individuals who disappeared first, we excluded the one case where the individual was later recorded again. ...
A central goal in evolutionary ecology is to identify factors that explain variation in reproductive success, i.e. in the number of offspring produced. In altricial birds, a substantial part of this variation is determined by the number of nestlings that die before fledging, but surprisingly little is known about the proximate causes of offspring mortality during the nestling period.
We used a uniquely comprehensive dataset of parental nestbox visits from seven breeding seasons to investigate the association between parental behaviour and nestling mortality in a population of blue tits ( Cyanistes caeruleus ).
In almost all nests that suffered complete brood mortality one of the parents had suddenly disappeared during the nestling stage. In contrast, parental disappearance in nests with partial brood mortality was rare and equally common as in nests with no brood loss.
With few exceptions, parents that disappeared during the nestling stage were never observed again and never returned to breed. In contrast, parents that remained after their partner disappeared were equally likely to be observed again or return to breed as parents of nests where both parents stayed. Visit rates at nests where a parent would disappear did not differ from those at nests where both parents stayed.
Taken together, our results show that ‐ in contrast to partial brood failure ‐ complete brood failure is almost always associated with the sudden and permanent disappearance of one of the parents, probably due to predation. Partial and complete brood mortality should be treated as distinct processes that have different underlying causes.
... PIT tags are lightweight, inexpensive and require no battery power, enabling large-scale deployment over long periods of time, and they can be used in both laboratory (Griffith et al. 2010;Weissbrod et al. 2013;Boogert et al. 2014; and field conditions (Broderick & Godley 1999;Bonter & Bridge 2011;Mariette et al. 2011;Steinmeyer et al. 2013;Adelman et al. 2015;Aplin et al. 2015;König et al. 2015). Although many individuals can be tagged, the antennas can only detect one individual at a time and only at fixed focal locations, such as nest boxes (Schlicht et al. 2015;Santema et al. 2017), feeders (Firth et al. 2016), or puzzle-boxes , which limits resolution for assessing interactions among individuals. ...
Recent advances in technology allow researchers to automate the measurement of animal behaviour. These methods have multiple advantages over direct observations and manual data input as they reduce bias related to human perception and fatigue, and deliver more extensive and complete datasets that enhance statistical power. One major challenge that automation can overcome is the observation of many individuals at once, enabling whole‐group or whole‐population tracking.
We provide a detailed description of an automated system for tracking birds. Our system uses printed, machine‐readable codes mounted on backpacks. This simple, yet robust, tagging system can be used simultaneously on multiple individuals to provide data on bird identity, position and directionality. Furthermore, because the backpacks are printed on paper, they are very lightweight. We show that our method is reliable, relatively easy to implement and monitor, and with proper handling, has proved to be safe for the birds over long periods of time.
We describe the deployment procedure of this system for a captive population of songbirds. We test different camera options, and discuss their advantages and disadvantages. In particular, we highlight how using single‐board computers to control the frequency and duration of image capture makes this system affordable and adaptable to a range of study systems and research questions.
The ability to automate the measurement of individual positions has the potential to significantly increase the power of both observational and experimental studies. The system can capture both detailed interactions (using video recordings) and repeated observations (e.g. once per second for the entire day) of individuals over long timescales (months or potentially years). This approach opens the door to tracking life‐long relationships among individuals, while also capturing fine‐scale differences in behaviour.
Parental investment in offspring comes in many forms, ranging from provisioning gametes and young to building nests and guarding territories. Patterns of parental investment—that is, which parent makes most or all of the investment—are linked to patterns observed around sexual selection (Chapter 11), with choosey mates being major investors. Certainty of maternity or paternity, the benefit of delivering care and the cost of lost opportunity with other mates all influence patterns of uniparental or biparental care. The cost and benefit of caregiving differ for parents and offspring, leading to parent–offspring conflict; infanticide is the most extreme expression of such conflict, and often results from male–male competition or females that have insufficient resources for successful parenting. Conflict among siblings can arise from competition for parental care. This leads to a discussion of aggression, which can reflect a variety of motivations. Among these is defense of territory, which brings the chapter full circle to nesting and territorial guarding.
Parents in biparental bird species have a conflict about how much each of them should invest in the current brood to optimize their reproductive success while not being exploited. Recently, it has been hypothesized that parents might attempt to resolve this conflict via taking turns in their provisioning visits. This implies that an individual will increase its working rate when their partner does, and that they will react with a delay in feeding if the partner starts delaying its visit. Experimental studies testing whether turn taking represents a behavioral strategy are surprisingly scarce and focus on the outcome of turn taking which are alternated visits. However, the adaptive significance of turn taking strongly relies on the response to a partner that increases or reduces care. Therefore, we investigate whether parents use the turn taking rules by performing an experimental manipulation on only one of the parents. To this end, we handicapped male blue tits (Cyanistes caeruleus) by feather clipping and recorded parental feeding behavior. Surprisingly, handicapped males did not have lower visit rates or altered turn taking levels, whilst their female partners had higher visit rates and lower turn taking levels when compared to the control. Females responded to the handicap of their partners, which likely reduced the males' parental capacity, but the females' response was independent of the males' rate of provisioning. Our study highlights that behavioral strategies are flexible within pairs and that these can change at the individual level in response to sudden changes in individual state.
A nest of begging chicks invites an intuitive explanation: needy chicks want to be fed and parents want to feed them. Surprisingly, however, in a quarter of species studied, parents ignore begging chicks. Furthermore, parents in some species even neglect smaller chicks that beg more, and preferentially feed the biggest chicks that beg less. This extreme variation across species, which contradicts predictions from theory, represents a major outstanding problem for the study of animal signalling. We analyse parent-offspring communication across 143 bird species, and show that this variation correlates with ecological differences. In predictable and good environments, chicks in worse condition beg more, and parents preferentially feed those chicks. In unpredictable and poor environments, parents pay less attention to begging, and instead rely on size cues or structural signals of quality. Overall, these results show how ecological variation can lead to different signalling systems being evolutionarily stable in different species.
Understanding how sexual conflict influences male and female parental decisions is a long-standing problem in behavioral ecology. Until now, most research on sexual conflict over parental care has focused on behavioral mechanisms mediating the resolution of this conflict through negotiation between parents. Here, we review evidence suggesting that maternal effects that alter offspring phenotypes may provide females with a mechanism for manipulating male care. We show that empirical studies on the role of maternal androgens in birds with biparental care provide no support for female manipulation of male care. However, we argue that it would be premature to conclude that maternal androgens play no role in female manipulation of male care given methodological problems in previous work. We then identify a number of additional mechanisms by which females may manipulate male care, including egg components other than androgens, egg size, and egg coloration. We show that there is good evidence that egg coloration affects male care, suggesting that this mechanism warrants further research. We also highlight that current evidence is derived from studies using experimental design that target specific candidate mechanisms, such as maternal androgens. Given the multitude of candidate mechanisms, we discuss an alternative approach based on targeting ecologically relevant prenatal conditions, such as food availability, and monitoring subsequent effects on candidate mechanisms, offspring phenotypes, and male and female care. Finally, we argue that it is timely to extend this work beyond birds with biparental care to include other taxa and species with uniparental male care and cooperative breeding.
The aim of this study is to describe and investigate geographic variation of Blue Tit Parus caeruleus song. We recorded songs at seven sites situated in the French Mediterranean region, five on Corsica and two on the mainland of southern France. Blue tits from these two regions belong to two subspecies differing significantly in body size. Both subspecies inhabit two distinct vegetation types, broad-leaved deciduous versus evergreen woodland. We analysed 570 songs recorded. On the mainland Blue Tit song was characterised by the presence of a rapid trill. This was not the case on Corsica, where the variation in song was also much more pronounced than on the mainland. The smaller subspecies of Corsica produced higher song frequencies and shorter songs. The frequency and the duration of intervals between notes differed between the songs of the two vegetation types on Corsica. On the mainland no such difference occurred. These results suggest that both body size and vegetation structure account for some of the geographic variation observed in Blue Tit song.
Parent-offspring conflict theory predicts that begging behaviour could escalate continuously over evolutionary time if it is not prevented by costliness of begging displays. Three main potential physiological costs have been proposed: growth, immunological and metabolic costs. However, empirical evidence on this subject remains elusive because published results are often contradictory. In this study, we test for the existence of these three potential physiological costs of begging in house sparrow (Passer domesticus) nestlings by stimulating a group of nestlings to beg for longer and another group for shorter periods than in natural conditions. All nestlings were fed with the same quantity of food. Our study involves a long-term experimental treatment for begging studies (five consecutive days). Long-term studies frequently provide clearer results than short-term studies and, sometimes, relevant information not reported by the latter ones. Our long-term experiment shows (i) a clear effect on the immune response even since the first measurement (6 hours), but it was higher during the second (long-term) than during the first (short-term) test; (ii) evidence of a growth cost of begging in house sparrow nestlings not previously found by other studies; (iii) body condition was affected by our experimental manipulation only after 48 hour; (iv) a metabolic cost of begging never previously shown in any species, and (v) for the first time, it has shown a simultaneous effect of the three potential physiological costs of begging: immunocompetence, growth, and metabolism. This implies first, that a multilevel trade-off can occur between begging and all physiological costs and, second, that a lack of support in a short-term experiment for the existence of a tested cost of begging does not mean absence of that cost, because it can be found in a long-term experiment.
Begging in birds is a complex behaviour used by nestlings to solicit feeds from caregivers. Besides calling when parents are present, nestlings of some species also perform less conspicuous repeat calls when parents are absent. The fact that these calls are produced when parents are not at the nest does not mean that parents cannot hear them when they approach the nest or forage in its vicinity. In this study, we experimentally investigated the relationship between parent-absent repeat calls (ARC) and frequency of parental visits, considering parent/offspring communication as a possible implication of these acoustic signals. A playback experiment was conducted to detect changes in parental investment in response to increases in parent-ARC, expecting a differential sexual response. Results showed that females clearly responded to repeat calls, increasing their visit rate significantly with respect to females that received the control treatment. Males, on the contrary, did not change their visit rate in response to the treatment. This result provides evidence for a role of parent/offspring communication in parent-absent repeat calling, an additional function to sibling negotiation processes. The sex-specific response that we found is in agreement with previous studies that have found that females are more responsive than males to variation in solicitation and hunger signals performed by nestlings.
When parent-offspring relations in sexually reproducing species are viewed from the standpoint of the offspring as well as the parent, conflict is seen to be an expected feature of such relations. In particular, parent and offspring are expected to disagree over how long the period of parental investment should last, over the amount of parental investment that should be given, and over the altruistic and egoistic tendencies of the offspring as these tendencies affect other relatives. In addition, under certain conditions parents and offspring are expected to disagree over the preferred sex of the potential offspring. In general, parent-offspring conflict is expected to increase during the period of parental care, and offspring are expected to employ psychological weapons in order to compete with their parents. Detailed data on mother-offspring relations in mammals are consistent with the arguments presented. Conflict in some species, including the human species, is expected to extend to the adult reproductive role of the offspring: under certain conditions parents are expected to attempt to mold an offspring, against its better interests, into a permanent nonreproductive.
Nestlings can employ a combination of tactics to obtain provisioning from the parents. In this observational study, we examined whether nestling begging behavior reflects hunger level and how parents respond to nestling begging in the Black-billed Magpie Pica pica by putting small video-cameras in six Magpie nests. Our results revealed a strong effect of nestling begging behavior on parental feeding. Begging earlier than others and stretching the neck towards the parent was important in inducing parental provisioning regardless of age of the nestlings. Being closer to the nest entrance slightly increased the chance of being fed, but did not influence parental feeding priority. The number of nestling begging events increased with the time interval since the last feeding, which indicates that begging frequency reflects the hunger level of the brood. However, in contrast to what can be predicted when begging behavior reflects hunger levels of nestlings, nestlings increased their begging level when parents provided more feedings in the previous visits and vocalized begging negatively affected the probability and the order of being fed by the parent. In addition, sensitivity in begging behavior and parental feeding decisions depended on nestlings' age, which suggests a possibility that parental feeding decisions change with growth stages of nestlings. Our results imply that begging behavior and food allocation in Magpies does not solely determined by the hunger level of nestlings.
Introduction Passive integrated transponder (PIT) tags offer a useful technique for monitoring animal activity in the wild. PIT tags, designed for implantation, do not require batteries and, thus, potentially, have an unlimited lifespan. These tags permit collection of data without handling or disturbing animals after being equipped with a PIT tag. Placing antenna at sites that are known to be regularly visited by tagged individuals, such as nests or feeders, could be used to collect automated data that provide information about behaviour (e.g. roosting, feed-ing activity, and movements) and may allow sur-vival estimation. PIT tags have been used to quantify the provi-sioning and feeding behaviour of birds (Boisvert & Sherry 2000, Ballard et al. 2001, Freitag et al. 2001, Ottosson et al. 2001, Weimerskirch et al. 2001), to monitor the survival of individuals (Becker & Wendeln 1997, Dittmann & Becker 2003, Gendner et al. 2005) and to identify nests in the wild (Booms & McCaffery 2007). To date, PIT tags have been used primarily in large adult birds (Weimerskirch et al. 2001, Ballard et al. 2001, Gauthier-Clerc et al. 2004, Low et al. 2005), but also in chicks of large birds (e.g. Carver et al. 1999, Applegate et al. 2000, Jamison et al. 2000, Gauthier-Clerc et al. 2004). Investigators have reported no negative effects of these tags on behav-iour or survival (Clarke & Kerry 1998, Carver et al. 1999, Jamison et al. 2000, Gauthier-Kenward et al. 2001, Clerc et al. 2004, Low et al. 2005).
Offspring should demand more food than the optimal amount for the parents to bring (parent–offspring conflict), and models
on the evolution of parent–offspring communication suggest that an equilibrium is reached when the costs associated with begging
make it unprofitable for the offspring to increase its level of begging. Empirical evidence for this cost, however, is mixed,
and the conclusions of most of authors are that begging is inexpensive. In this study, the existing empirical evidence for
this cost is reviewed. One cost proposed is the attraction of predators due to begging calls, but empirical support for this
cost is low. However, studies performed cannot dismiss such a cost. Another possible cost is the metabolic expenditure, but
empirical evidence for this cost is mixed, with some works contending that it is low, while others deem it important. Other
possible metabolic costs have not been studied. A loss of inclusive fitness may be an important cost for the evolution of
begging, and robust empirical evidence does exist for this cost. Costs associated with brood reduction also are reviewed.
In conclusion, there is not enough empirical evidence to test the models on the evolution of begging. Most costs proposed
have not yet been studied or the approach used has been insufficient to reject the null hypothesis (i.e., absence of cost).
Interactions among parents, offspring and the environment are a critical aspect of parental care. Begging by offspring usually results in increased parental provisioning. Yet, parents also vary their behaviours to reduce offspring predation. Both begging sounds and provisioning activity can increase risk of nest predation. We predicted in a high nest-predation environment, parents would satiate young and reduce begging by increasing food load but maintaining the same provisioning rates. We also assessed whether increased begging was beneficial to offspring and whether parents changed the allocation of food to particular nestlings. We increased whole-brood begging via playbacks at nests of a tropical passerine bird, the western slaty antshrike, Thamnophilus atrinucha. We observed that parents increased provisioning rates and reduced food load in response to elevated begging. Selection may therefore favour feeding hungry nestlings even when predation risk is elevated, or begging sounds may place offspring at a higher risk than increased activity. Parents reduced the time between arrival to the nest and feeding of nestlings, potentially to reduce begging sounds. Exaggerated begging did not appear to be beneficial to offspring since parents did not deliver more food. Parents switched to preferentially feed the closest offspring during the begging treatment. This suggests that, under elevated begging, parents either allowed sibling competition to influence feeding decisions, or fed the closer nestling to reduce the time between arrival to the nest and feeding. Studying species in different environments provides insight into how ecological factors such as nest predation influence parental behaviour.
The evolutionary conflict over the amount of resources transferred between a parent and its offspring may be resolved by honest signalling of ‘need’ by offspring and parental investment in relation to signalling level. In birds, biparental care is the norm and evidence that male and female parents differ in their investment pattern in individual offspring is growing. In an experiment on great tits,Parus major, we investigated how and why parents differ in food allocation when responding to similar chick signals, which supposedly uniquely reflect the chick's nutritional condition. Nestling hunger level was manipulated by food deprivation and hand-feeding. Subsequent filming revealed that parents fed from significantly different locations on the nest and thereby forced chicks to choose between them when competing for favourable positions. Deprived nestlings approached, and fed ones retreated (or were displaced by siblings) from, positions near the female. No such behaviour was observed towards the male. Females allocated more feeds than males to the food-deprived nestlings. The results are discussed in terms of nestling competition for access to ‘begging patches’. By varying their ‘begging patch’ value, parents may exploit competitive inter-sibling dynamics to influence the outcome of competition among chick phenotypes (e.g. ‘need’, size, sex). Parent birds may thereby exert considerable control over the information content of chick begging behaviour.
Theoretical modelling of biparental care suggests that it can be a stable strategy if parents partially compensate for changes in behaviour by their partners. In empirical studies, however, parents occasionally match rather than compensate for the actions of their partners. The recently proposed "information model" adds to the earlier theory by factoring in information on brood value and/or need into parental decision-making. This leads to a variety of predicted parental responses following a change in partner work-rate depending on the information available to parents.
We experimentally test predictions of the information model using a population of long-tailed tits. We show that parental information on brood need varies systematically through the nestling period and use this variation to predict parental responses to an experimental increase in partner work-rate via playback of extra chick begging calls. When parental information is relatively high, partial compensation is predicted, whereas when parental information is low, a matching response is predicted.
We find that although some responses are consistent with predictions, parents match a change in their partner's work-rate more often than expected and we discuss possible explanations for our findings.
Current models of parent-offspring communication do not explicitly predict the effect of parental food supply on offspring demand (ESD). However, existing theory is frequently interpreted as predicting a negative ESD, such that offspring beg less when parental supply is high. While empirical evidence largely supports this interpretation, several studies have identified the opposite case, with well-fed offspring begging more than those in poorer condition. Here, we show that signalling theory can give rise to either a negative or a positive ESD depending on the precise form of costs and benefits. Introducing variation among parents in the cost of care, we show that the ESD may change sign depending upon the quantitative relation between two effects: (i) decreased supply leads to increased begging because of an increase in marginal fitness benefit of additional resources to offspring, (ii) decreased supply leads to reduced begging because it is associated with a decrease in parental responsiveness, rendering begging less effective. To illustrate the interplay between these two effects, we show that Godfray's seminal model of begging yields a negative ESD when care is generally cheap, because the impact of supply on the marginal benefits of additional resources then outweighs the associated changes in parental responsiveness to begging. By contrast, the same model predicts a positive ESD when care is generally costly, because the impact of care costs on parental responsiveness then outweighs the change in marginal benefits.
Begging by nestling birds has been used to test evolutionary models of signalling but theory has outstripped evidence. Eavesdropping predators potentially impose a cost on begging that ensures signal honesty, yet little experimental evidence exists for such a cost at active nests because the use of artificial nests, long playback bouts and absence of parents may have exaggerated costs. We broadcast short periods (1 h) of either nestling vocalizations or background noise at active white-browed scrubwren, Sericornis frontalis, nests. Nestlings called naturally during both treatments, allowing us to test whether elevated calling increases risk, a key but rarely tested assumption of evolutionary models. Predators visited nests exclusively during periods of elevated calling. Furthermore, playbacks affected neither adult visits nor nestling activity, suggesting that calling alone attracted predators. Adults gave alarm calls and nestlings usually called less when predators approached nests. Predation risk to broods is, therefore, likely to fluctuate substantially over short periods of time, depending on nestling hunger and whether adults or young have detected predators. This study confirms a present-day cost of nestling begging, demonstrates that this cost can be incurred over short periods and supports the importance of parent-offspring antipredator strategies in reducing predation risk.
Models of biparental care predict that parents should compensate incompletely for any change in their partner's investment. Experimental tests have, however, yielded results that range from full compensation, through a lack of any reaction, to a matching response. Here we suggest a new, adaptive explanation for such variation. Building on an approach developed by McNamara et al., we incorporate uncertainty regarding brood need or value into a game-theoretical model of biparental negotiation over offspring care. We show that when each parent has only partial information, greater effort invested by one serves as a signal to the other of brood need. This favors a matching response by the focal parent's mate, whereas the impact of increased effort on the marginal value of investment favors a compensatory response. The net outcome depends on the relative strength of these two effects. The greater the variation in brood need compared with parental state, the weaker the predicted level of compensation, and the more likely matching is to occur. Our model also suggests why males and females might respond differently to each other. If there is an informational asymmetry between them, then the parent that is better informed about brood need should work harder, respond more strongly to changes in brood need, be less sensitive to changes in the cost of feeding, and compensate more strongly for changes in partner effort. If the asymmetry is very great, the poorly informed parent may even match changes in its partner's work rate. Copyright 2006.
Evolutionary theory of parent-offspring conflict explains begging displays of nestling birds as selfish attempts to influence parental food allocation. Models predict that this conflict may be resolved by honest signaling of offspring need to parents, or by competition among nestmates, leading to escalated begging scrambles. Although the former type of models has been qualitatively supported by experimental studies, the potential for a begging component driven by scramble competition cannot be excluded by the evidence. In a brood-size manipulation experiment with great tits, Parus major, we explored the scramble component in the begging activity of great tit nestlings by investigating the mechanisms of sibling competition in relation to brood size. While under full parental compensation, the feeding rate per nestling will remain constant over all brood sizes for both types of models; the scramble begging models alone predict an increase in begging intensity with brood size, if begging costs do not arise exclusively through predation. Great tit parents adjusted feeding rates to brood size and fed nestlings at similar rates and with similar prey sizes in all three brood-size categories. Despite full parental compensation, the begging and food solicitation activities increased with experimental brood size, whereas nestling body condition deteriorated. These findings support a scramble component in begging and suggest that the competition-induced costs of food solicitation behavior play an important role in the evolution of parent-offspring communication. Copyright 2003.
In a colony of Leach's Storm-Petrels (Oceanodroma leucorhoa) on Kent Island, New Brunswick, i chicks were rotated on a daily basis through n nests to produce i/n chick-equivalents of food requirement, increasing by small increments from 1 (i = 6, n = 6) to 2 (i = 2, n = 1), between ages 10 and 50 days. Food delivered each night (SUM) was estimated by 24-h increments in chick mass. In nonexperimental nests SUM varied significantly among pairs, and chick mass varied in direct relation to SUM. Adults tending experimental nests did not respond to increased food demand, and chick mass decreased with increasing chick-equivalent per nest. After rotations were terminated, the mass of most chicks increased quickly to normal levels. These results suggest that the average amount of food delivered daily by each parent is determined independently of food demand and that chicks attain a mass that balances a fixed food intake against food requirement, which varies in direct relation to mass.
The begging behavior of immature Zebra Finches has both visual and acoustic components. Begging nestlings gape at their parents, exposing characteristic mouth markings and a moving tongue. They also emit begging calls. Both components undergo changes as the offspring mature, and there is a shift from the visual to acoustic modality as the primary stimulus for feeding. Recorded fledgling begging calls were broadcast inside the cages of Zebra Finch parents with offspring. These begging calls stimulated parental feeding and other behaviors associated with feeding. The offspring also responded to recorded calls by showing begging behavior. Parents were sensitive to recorded begging calls from approximately day 16 to day 28 after the first offspring hatched, although there was substantial variation in these times among pairs of parents.
Blue Tit vocalisaties were studied in the field research area of the Peerdsbos, a mixed deciduous woodland north of Antwerp Belgium during from August 1980- July 1984. The current study is based on about 100 hours of recorded vocalisations and observations during a sound transect along a fixed route from December 1981 to July 1983. At the same time the territorial behavior of 16 Blue Tit pairs were studied in more detail during spring of 1982. Fifteen non-song calls are described. For each call a sonogram is shown, the behavioural context is described and the occurrence during the year is discussed. As concerns song the study yielded 10 songs. The Blue Tit is a discontinuous singer with an average repertoire size of 5.25 song types (range 3-8). Several vocalisations are used in difference contexts and are therefore assumed to have difference functions. These include several song types; S2 also has an anti-predator and alarm function; S5 and S10 mostly used in the morning chorus are often used in escalated conflicts and during mobbing when ground predators are being attacked. They may therefore also have an aggressive function.
Environmental factors such as heat and solar radiation directly affect the open‐cup nest environment and can impact nestling body temperature.
The aim of our research was to understand how open‐cup passerine nestlings use behavioural thermoregulation to mitigate solar heat gain and to measure the metabolic cost of begging and non‐begging activity under three light treatments: room light (<2 Wm ⁻² ), simulated shade (500 Wm ⁻² ) and simulated sun (1000 Wm ⁻² ). Our study coupled behavioural (field) and physiological (laboratory) experiments to explore the adaptive behavioural response of passerine nestlings to nest cup nanoclimates (sun and shade), using the common grackle ( Quiscalus quiscula ) as a model species.
Non‐begging behaviour was evaluated in the field by randomly assigning nestlings to a homogeneous (all sun) or heterogeneous (sun and shade) nest environment; measuring body temperature ( T b ); and identifying behaviours from videotaped footage. The T b of nestlings without access to shade was significantly higher, and nestlings spent more time moving and panting, suggesting an increased metabolic expenditure. To test this, we duplicated the insolation nanoclimate under laboratory conditions using a 1·0 KW Sciencetech Illumination System and measured the energetic cost of begging and non‐begging activity using open‐system respirometry on non‐irradiated and irradiated nestlings. Our results suggest that, in grackle nestlings, the relationship between activity (begging and non‐begging) and energy expenditure is context‐dependent.
Our results identified: (i) a reduction in energy expenditure associated with accessing the shade; (ii) expenditure on non‐begging activity equalled or exceeded expenditure on begging activity; and (iii) a potential behavioural constraint on begging imposed by exposure to a homogeneous sun environment (sun without access to shade). The combination of context‐dependent costs and constraints suggests the potential for strategic costs associated with the heterogeneous nest environment .
Blue Tit vocalisations were studied in the field research area of the Peerdsbos, a mixed deciduous woodland north of Antwerp Belgium during from August 1980- July 1984. The current study is based on about 100 hours of recorded vocalisations and observations during a sound transect along a fixed route from December 1981 to July 1983. At the same time the territorial behavior of 16 Blue Tit pairs were studied in more detail during spring of 1982. Fifteen non-song calls are described. For each call a sonogram is shown, the behavioural context is described and the occurrence during the year is discussed. As concerns song the study yielded 10 songs. The Blue Tit is a discontinuous singer with an average repertoire size of 5.25 song types (range 3-8). Several vocalisations are used in difference contexts and are therefore assumed to have difference functions. These include several song types; S2 also has an anti-predator and alarm function; S5 and S10 mostly used in the morning chorus are often used in escalated conflicts and during mobbing when ground predators are being attacked. They may therefore also have an aggressive function.
Although sleep is fundamental for survival, not much is known about sleep behaviour in free-living animals and between-individual variation in sleep patterns has hardly been studied, except in humans. We analysed sleep behaviour in a free-living population of blue tits in southern Germany. We recorded individuals roosting in nestboxes between November and April using infrared-sensitive cameras. We investigated the following sleep parameters: time of entering and leaving the nestbox, sleep onset, awakening time, sleep duration, midpoint of sleep, latency to sleep and frequency and duration of nocturnal awakenings. Sleep onset, awakening time and sleep duration followed seasonal changes in daylength. Blue tits slept ca. 4.8 h longer in winter than in spring. During the night, birds woke up between 23 and 230 times, but this did not change seasonally. Local light conditions influenced awakening time: birds at brighter locations woke up earlier. Females slept on average 15 min longer per night than males and this sex difference became more pronounced in early spring. Although females spent a greater proportion of the night awake than males, they still slept more overall. First-year birds spent more time in the nestbox after waking up and left the nestbox later in the morning than older individuals. Repeatability estimates showed that individuals were consistent in their sleep behaviour over the 2-year study period. Our results indicate that sleep patterns are individual-specific traits in blue tits. We suggest that the observed sex difference in sleep duration is caused by sexual selection.
To the extent that shivering is an honest, perhaps unfakable indicator of a biologically relevant need for warmth, the vocalizations associated with it appear to be honest signals indicating the presence of that need. Results are also consistent with a recent theoretical model of honest signalling of need by offspring, but it remains to be determined whether honest solicitation of warmth prevails when Pelecanus erythrorhynchos chicks are in naturally competitive situations at the nest. -from Author
Despite the fact that in many bird species offspring are provisioned by two parents, few studies to date have examined the implications of biparental care for offspring solicitation behaviour. Male and female parents can differ in their potential value to individual offspring if they follow different allocation rules and/or have different provisioning rates. If such differences occur, offspring should use different rules when soliciting to the male and female parent. This study looked at how the begging behaviour of nestling blue tits, Cyanistes caeruleus, is influenced by their hunger, size and by the sex of the provisioning adult. Nestling hunger was manipulated across size ranks, using periods of hand feeding or food deprivation. While nestling hunger influenced all aspects of nestling begging behaviour, nestling size and the sex of the provisioning adult only affected the position of nestlings in the nest cup. When hungry, nestlings moved closer to the male parent and the largest nestlings in a brood primarily obtained the closest positions. This may be the result of offspring responding to a difference between the sexes in parental food allocation rules.
Descriptive studies of provisioning in cooperatively breeding superb fairy-wrens, Malurus cyaneus, show that females are responsive to the needs of the brood, increasing nest visits with brood size and age. Both dominant and helper males provision at a constant rate regardless of brood size and age, but dominant males reduce provisioning as the number of helpers increases. This reduction could reflect load lightening or reduced relatedness, as dominants are more likely to be cuckolded by extragroup males when they have helpers. To distinguish between these alternatives we conducted playback experiments that augmented the natural begging of 6-day-old nestlings with the calls of 4-day-old nestlings (control) or the much louder calls of 10-day-old nestlings (experimental treatment). We presented playbacks to the female alone, all birds, or males alone. We predicted that females would always respond to increased begging, helper males would not respond, and dominant males would always respond (load-lightening hypothesis) or respond when they had paternity in the brood (relatedness hypothesis). Contrary to these predictions, males always responded and females did not. Females may require additional stimulation or alternative cues in order to respond. Dominant males spend less time at the nest, and may judge nestling need on the basis of simpler cues. They may always feed as little as possible to minimize their commitment to nestlings to which they are unlikely to be related. However, they may increase their response when they lack helpers, or females are unable to meet the demands of the brood.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .
The origin of polygyny and its effects on reproductive success was studied in a population of the blue tit, Parus caeruleus. Each year about 20% of males and about 35% of females engaged in a polygynous mating. Polygynous males fledged more young and survived better than monogamous ones. On average primary females did not fledge fewer young than monogamous ones, but they paid a cost because they received less male help. Secondary females had lower reproductive success than either primary or monogamous females. Polygyny could arise when a male annexed a neighbouring territory after the owner disappeared (replacement polygyny), or when a female settled on an already occupied territory. Females either settled early during winter (year-round polygyny) or during the breeding season (successive polygyny). Replacement and successive polygyny seem to result from a female-biased sex ratio during the breeding season. This biased sex ratio was caused by a female-biased immigration from January to March. Predation of males could also be significant. The biased sex ratio caused severe competition for breeding opportunities between females. Settlement of floater females was limited as a result of strong female-female aggression, especially early in the breeding season. In this study, the polygyny-threshold model could not be used to explain polygyny, since one of its basic assumptions, that females are free to settle where they choose, was violated. It is argued that the model can work on a larger scale.
Information warfare occurs when factions use and manage information to gain an advantage over their rivals. It is common in diverse contexts ranging from identity fraud to industrial espionage, from biotech war to military campaigns. The information warfare plays an important role in influencing the outcome of the parent–offspring conflict, the evolutionary conflict of interest between parents and their young over the provision of parental investment. In principle, the asymmetry in knowledge can counterbalance any asymmetry in physical prowess between rivals, and the more knowledgeable party might gain the upperhand. For this reason, information warfare is aptly applied to the context of parent–offspring conflict, because young animals in conflict with their parents are often placed at a disadvantage by their relatively small size and weaker physical power. Two outcomes to parent–offspring conflict are possible. The first is an evolutionarily stable resolution and the alternative outcome to parent–offspring conflict is an unstable arms race through evolutionary time.
Interest in nestling begging arises from the theoretical conflict over resource allocation between parents and their offspring.
This conflict was first proposed by Trivers (1974), who suggested that an individual offspring is selected to obtain a greater proportion of resources than the parent is selected
to give. That is, a parent is equally related to each offspring in each brood by half, whereas a nestling is more highly related
to itself (i.e., 1.00) than to its present or future siblings (i.e., 0.50-0.25, on average). Conflict between parent and offspring
can be expressed throughout the period of parental care from conception through independence, during which offspring are selected
to elicit parental investment for a period exceeding the optimum for the parent. Trivers (1974) suggested an offspring is able to “compete” effectively with its parent through psychological manipulation. By begging until
its needs have been met, the offspring indicates its degree of distress (for example, its requirement for food) and thereby
encourages a higher level of parental investment. In such a system, any offspring signaling a “dishonest” (excessive) level
of need would benefit from receiving a level of parental
Various studies have reported that extrapair young outperform their within-pair half-siblings in fitness-relevant traits, suggesting indirect benefits of extrapair copulations for females. Recent studies, however, suggest that potential confounding maternal effects such as laying and hatching order may have been overlooked. In this study on blue tits, Cyanistes caeruleus, we investigated fledging behaviour, a potentially fitness-relevant trait, in relation to the paternity status of the offspring. We tested whether extrapair young differed from within-pair young in fledging order per se and after we controlled for hatching order, a potential confounding maternal effect. We found that male, but not female, extrapair young fledged earlier than their within-pair nestmates. This effect was partly mediated by the higher body mass of extrapair young, which is a major determinant of fledging order independent of paternity status. However, even when we controlled for body mass, a correlate of hatching order, male extrapair young still fledged earlier than their same-sex half-siblings, indicating that male extrapair nestlings may be at an advantage over their siblings. (c) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
We describe the use of subcutaneous passive integrated transponder (PIT) tags in nestling and adult Great Tits Parus major. We investigated whether subcutaneous PIT tags affected fledging success, winter condition, survival and/or recruitment. We found no negative effects of PIT tags on any of these measures either in juveniles or in adults. Subcutaneous PIT tags have the advantage that the risk of tag loss is negligible and that further data collection can be automated. The subcutaneous implantation of PIT tags provides a promising technique for researchers aiming at gathering short or long-term data without the need to handle or disturb small birds after implantation.
ABSTRACT Although individually distinct begging calls may permit parents to recognize their offspring, birds nesting in dense breeding colonies where fledglings intermingle might benefit from additional adaptations. For example, if the calls of all nestlings in a brood were similar, parents would need to recognize only one brood call instead of the identity calls of each nestling. We recorded nestling Red-winged Blackbirds (Agelaius phoeniceus) to determine whether their calls function to identify individuals (identity call hypothesis) or broods (brood call hypothesis). We used spectrogram cross-correlation and dynamic time warping as well as call duration, peak frequency, and frequency range to estimate the similarity of begging calls of nestling Red-winged Blackbirds. We recorded individual nestlings on day 5 and on day 9 of the nestling period to determine whether calls of individuals were more similar than calls of different nestlings, and whether calls of broodmates were more similar than calls of nestlings from different broods. We found that calls of 8-d-old individuals were more similar than calls of different nestlings, but the calls of broodmates were not more similar than those of nestlings from different broods. These results were consistent with the identity call hypothesis. We then compared begging calls of pairs of nestlings recorded separately and together on day 9. We found that the calls of 8-d-old nestlings recorded together were more similar than when they were recorded separately. In addition, using playback of begging calls from normal broods and artificial “broods” constructed from the calls of single nestlings, we found that females returned with food sooner in response to the calls of single nestlings (with enhanced call similarity) than to those of normal broods. Our results suggest that similar begging calls may be beneficial for both nestlings and parents, with broodmates fed at higher rates when their calls are more similar and, after fledging, parents needing to recognize only one brood call instead of the identity calls of each fledgling.
Aunque las diferencias individuales en los llamados de reclamo les pueden permitir a los padres reconocer a su progenie, aves que nidifican en grandes colonias de anidación donde los polluelos pueden mezclarse pueden obtener beneficios mediante adaptaciones adicionales. Por ejemplo, si los llamados de todos los polluelos en el nido son similares los padres necesitarian reconocer solo un tipo de reclamo de los polluelos en vez de identificar llamados individuales de los polluelos. Grabamos polluelos de Agelaius phoeniceus para determinar si sus llamados son usados para identificar individuos (Hipotesis de la identidad del polluelo) o para identificar a la progenie (Hipotesis de la identidad de la progenie). Usamos espectrogramas de correlación cruzada y dinamica del tiempo de combeo al igual que la duración del reclamo, el pico de frecuencia y frecuencia del rango para estimar la similaridad de los llamados de los polluelos de Agelaius phoeniceus. Grabamos polluelos individuales de 5 y 9 días de nacidos para determinar si los llamados de los individuos eran más similares a llamados de otros polluelos y si los llamados dentro de una progenie eran ma similares a llamados de otra progenie. Encontramos que los llamados de polluelos de 8 días de nacidos eran más similares que los llamados de diferentes polluelos, pero los polluelos de una misma progenie no fueron más similares que polluelos de diferentes progenies. Esto resultados concuerdan con la hipotesis de la identidad del polluelo. Después comparamos los llamados de parejas de polluelos grabados por separado y los que fueron grabados juntos el día 9. Encontramos que los llamados de polluelos de 8 días de nacidos grabados juntos fueron mas similares que cuando los polluelos fueron grabados por separado. Adicionalmente, usando playback de llamado de polluelos de progenies normales y progenies “artificales” construidos basado en llamado de un solo polluelo, encontramos que las hembras regresaron más rapidamente con alimento en respuesta al llamado de un solo polluelo (con realzamiento en la similaridad del llamado) que para las progenies normales. Nuestros resultados sugieren que la similaridad en los llamados de los reclamos pueden ser beneficiosos tanto para los polluelos como los padres, en donde las tasa de alimentación es mayor cuando sus llamados son mas similares, y después de abandonar el nido cuando los padres necesitan reconocer un solo llamado de la progenie en vez de tener que identificar llamados individuales de cada volanton.
THE young of birds and mammals often solicit food from their parents in
ways that appear to be costly and to reduce their fitness1,
2. Thus birds in the nest beg vigorously for food, incurring
energetic costs and possibly attracting predators3; the
behaviour of young mammals requiring to suckle (bleating or crying, for
example) similarly appears costly1, 2. If solicitation is a
means by which the young communicate need to their parents, why has a
less expensive form of communication not evolved4? An answer
to this question is provided by the theory of parent-offspring conflict:
natural selection acting on genes expressed in the young will lead to
greater demands for parental resources than is optimal for the
parent1, 5. The accurate communication of offspring need is
evolutionarily unstable as offspring will be selected to demand extra
resources. Models of parent-offspring conflict have shown that an
evolutionarily stable equilibrium can exist at which an offspring
solicits resources in a way that reduces its fitness, and a parent
provides extra resources to prevent further expensive
solicitation6-11. I present an alternative explanation for
costly solicitation by showing that the level of offspring solicitation
can be a true reflection of offspring need as long as solicitation is
costly and the benefits of extra resources increase with need. My
analysis suggests that the parent normally allocates resources using
accurate information about the condition of the young. The requirement
that the signalling system is costly is a direct consequence of the
potential for parent-offspring conflict.
Passive integrated transponders (PITs) are increasingly used to study behaviour in small passerines. However, to ensure the reliability of such studies, knowledge of long-term fitness consequences of equipping passerines with PITs is crucial. We quantify the effects of fitting PITs, injected subcutaneously or glued to colour rings, on fitness in house sparrows Passer domesticus. Relative annual fitness was assessed with the delifing method as an individual's annual contribution to population growth rate. We found no evidence for adverse fitness effects in individual birds fitted with PITs compared with individuals without PITs, independent of the methods of fitting the tags. Our results provide a solid basis for the assumption that such logging devices are safe to use in small passerines and that PITs will most probably not affect the outcome of studies with respect to population dynamics and fitness components.
Despite the success of kin selection in explaining helping-at-the-nest among communally breeding birds, we know almost nothing
about how helpers regulate their chick-feeding effort. This is especially interesting given how much we now know about parental
provisioning `rules-of-thumb' and the evolution of chick begging as an honest signal of `need'. This study explores the provisioning
rules of helpers and parents in Arabian babblers (Turdoides squamiceps), using tape play-backs to supplement chick-begging signals and increase apparent brood demand. In all eight groups tested,
both helpers and parents fed older, noisier broods at higher rates. Total provisioning rates to nests increased during begging
play-back days compared to control days. Absolute provisioning rates by helpers and the scale of their responses to play-backs
were statistically indistinguishable from those of parents. In both helpers and parents, increases in nest visits during play-backs
were associated with reductions in foraging distance from the nest and increases in size of prey delivered. Older birds of
both sexes delivered slightly larger prey items, possibly reflecting differences in foraging ability due to experience. These
results are consistent with the idea that, like the parents, helpers-at-the-nest in Arabian babblers provision nestlings as
part of a strategy of investment, irrespective of helper age, dominance status or sex. In this species, high relatedness within
groups may provide parents and helpers with similar kin-selected fitness benefits, although the mutualistic advantages to
helpers from simply augmenting group sizes cannot be ruled out.
The begging behavior of birds is thought to influence the allocation of food within the brood (allocation function) or to
increase the total amount of food delivered to the brood (delivery function). Considering the nature of the feeding activity
of passerines, in which hundreds of feeding events occur in a single day, parents may not necessarily decide the amount of
resources allocated to each nestling/brood during a single feeding event. To examine this possibility, the relationship between
begging intensity and parental responses to allocation and delivery functions was tested and modeled at multi-temporal scales
in the barn swallow (Hirundo rustica). Comparison of models revealed that barn swallow parents differed in the temporal scales at which they respond to nestlings
with respect to these two functions. While barn swallow parents decide which nestling to feed at a focal feeding event according
to chick begging of the focal feeding event, they integrated past information on total begging effort to determine delivery
rates to their offspring during the 14 and 6min prior to the focal feeding event in males and females, respectively. These
findings highlight that it is important to investigate parental response to begging at appropriate temporal scales when analyzing
begging functions.
KeywordsBarn swallow–Begging–Food allocation–Food delivery–
Hirundo rustica
–Temporal scale
It has been suggested that nestlings use begging to increase their share of parental resources at the expense of current
or future siblings. There is ample evidence that siblings compete over food with nestmates by begging, but only short-term
effects of begging on parental provisioning rates have been shown. In this study, we use a new experimental design to demonstrate
that pied flycatcher (Ficedula hypoleuca) nestlings that beg more are able to increase parental provisioning rates over the major part of the nestling period, thus
potentially competing with future siblings. Parents were marked with microchips so that additional begging sounds could be
played back when one of the parents visited the nest. By playing back begging sounds consistently at either male or female
visits, a sex difference in provisioning rate that lasted for the major part of the nestling period was induced. If each parent
independently adjusts its effort to the begging intensity of nestlings, begging may also be the proximate control mechanism
for the sexual division of labour.
Altricial nestlings solicit food by begging and engaging in scramble competition. Solicitation displays can thus signal both hunger and competitive ability. I examined nestling solicitation and parental responses in crimson rosellas (Platycercus elegans), a species in which parents engage in complex patterns of food allocation and appear to control the distribution of food. By manipulating the hunger of individual chicks and entire broods, I assessed how chick behaviours and parental food allocation varied with hatching rank, level of hunger, and intensity of nestling competition. Last-hatched chicks begged more than first-hatched chicks irrespective of individual hunger levels. The two parents combined fed individually hungry chicks more, but mothers and fathers varied in their responses to begging chicks: fathers fed last-hatched chicks in proportion to their begging intensity, whereas mothers fed chicks equally. Since fathers generally allocate more food to first-hatched chicks, fathers appear to use begging rates to adjust food allocation to non-preferred chicks within the brood. When I manipulated brood hunger levels, begging rates increased for first- and last-hatched chicks suggesting that chick begging rates are sensitive to the level of competition. This study shows that begging by rosella chicks does not correlate with hunger in a straightforward way and that the primary patterns of food allocation by parents are not influenced by chick begging. Thus the benefits of increased begging may be limited for nestlings in this species.
Cooperative provisioning dynamics between members of a pair in biparental systems has received a lot of attention, both empirically and theoretically. The dynamics of provisioning in cooperatively breeding groups, however, remains poorly understood. Such groups often include unrelated helpers that may have very different provisioning rules from related helpers and parents, since they accrue different types of fitness benefits from helping. The bell miner, Manorina melanophrys, provides an ideal system in which to investigate cooperative provisioning, because substantial levels of care are provided by a number of unrelated helpers per nest. We experimentally increased brood demand via targeted begging playbacks during nest visits of either breeding males or unrelated male helpers. Both types of males used similar behavioural investment rules, significantly increasing food delivery rate during playback relative to control periods. Surprisingly, all other provisioners also increased their visit rates during playbacks, although to a lesser extent. This could only have been in response to the increase in visits by the target individuals, suggesting an additional indirect mechanism by which individuals in this cooperative setting assess brood demand. The resultant overall increase in food delivery during the playback periods caused nestlings to show the expected reduction in their own begging and an increase in body mass gain. It is therefore interesting how similar the evolved provisioning responses are for all types of group member, irrespective of whether such benefits of investment in the brood are derived via kin selection (fathers) or some future direct increase in fitness (helpers).
I investigated the short-term regulation of parental provisioning rate in blue tits by videotaping the parents at the nest. An additional feeding experiment allowed a comparison between the behaviour of parents rearing their brood under normal and supplemented feeding conditions. Videotaping revealed that parents changed their provisioning rate as an immediate response to the absence of begging by chicks. When chicks did not beg for food, the parents solicited them with a particular call to make them open their beaks. Parents spent significantly longer away from the nest immediately after uttering these feeding calls. Provisioning rate returned to the usual levels as soon as the chicks started begging again, but supplemented parents took less time to do so than controls (i.e. parents not provided with additional food). Changes in provisioning rate had effects on both the type and size of prey brought to the brood. Females often responded to low brood demand by returning to the nest without food. Food-supplemented parents, but not controls, took larger larvae when they stayed away from the nest for longer. This suggests that parents in the supplemented group could use more time to reach good feeding sites or, more probably, increase their prey selectivity. Blue tits continually monitored the begging behaviour of their offspring and responded accordingly by adjusting their feeding rate, with immediate consequences for prey choice.
Nestling birds may honestly signal their need for food to provisioning adults, or begging might be a manipulative attempt to coerce additional food from providers, but in either case, providers respond to an increase in begging with an increase in feeding. We used playback of begging calls recorded from nestlings to determine whether male and female red-winged blackbirds increase their feeding rates in response to an apparent increase in begging. Both females and males fed broods at significantly higher rates after 5-min begging call playbacks than before, although only eight of 30 males were observed to feed nestlings in this study. In contrast, using the same playback design, neither females nor males altered their feeding rates significantly in response to broadcasts of noise. These results and others suggest that begging vocalizations are a basis for short-term adjustments in the rate at which nestling birds are provisioned. These results are also compared with those of a similar study of the same species, in which playback had no significant effect on rates of provisioning.
We explored behavioural adjustments made by parent house sparrows, Passer domesticus, when the nutritional condition of their dependent nestlings was improved experimentally. Male parents responded to artificially supplemented broods by increasing food deliveries, whereas female parents continued matching the already high rate of control females. Thus, parental care was not truncated in the face of fortified offspring, but actually escalated (ca. 17% more adult food deliveries overall). Supplemented nestlings showed a nonsignificant tendency to recruit into the adult breeding population more than controls. We propose that one important reason why male parents responded more strongly than their female partners centres on the lower marginal costs for additional male posthatching investment, specifically by demonstrating that increasing paternal investment is likely to confer higher fitness than alternative male activities.
Throughout the animal kingdom, distinctive behaviour by offspring commonly precedes and accompanies their provisioning by parents. Here, we assess empirical support for the recent theory that begging advertises offspring need, that parents provision young in relation to begging intensity, and that the apparently costly nature of begging ensures the reliability of the signal. While there is some support for the predictions of honest signalling models, empirical work has also revealed a host of complexities (such as the use of multiple signals) that existing theoretical analyses have only begun to address.
Game theoretical models of biparental care predict that a change in work rate by one parent should be met by incomplete compensation by its partner. However, in empirical studies on biparental birds, there has been some inconsistency in the direction and extent of the response, and the mechanism behind it has so far been unclear. Parents could be responding directly to partner work rate or indirectly via chick begging. In this study of great tits (Parus major), the work rate of one parent was increased experimentally by augmenting the begging of the chicks with playback of extra begging calls whenever the parent visited the nest. The playback had no effect on the chicks' begging behavior, so any change in the focal parent's behavior was a direct response to its partner's work rate over a short timescale. An experimental increase in care by either male or female parent led to an increase (to a lesser extent) in the work rate of its partner, which is counter to the decrease predicted by partial compensation models. This seemingly paradoxical result may reflect decisions made exclusively over a short timescale and is in keeping with new theoretical work, which takes into account the information content of partner work rates. Copyright 2006.
