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The Influence of the Pair-Bond and Age on the Breeding Biology of the Kittiwake Gull Rissa tridactyla
Journal of Animal Ecology
Abstract
1. The influence of changes in mate on the breeding biology of female kittiwakes (Rissa tridactyla) has been investigated over a 12-year period. 2. About 64% of the birds retained their mate from the previous breeding season, but older birds tended to change their mates less frequently than young birds. Of the birds which changed their mate, a third changed because their partner from the previous breeding season had died, but the mates of the remaining two-thirds were still present in the colony. 3. There was a strong tendency for birds to choose a mate of the same age, but this was less pronounced in older birds where the females more frequently paired with a younger male. 4. A change of mate was three times more likely if the pair had failed to hatch their eggs in the previous breeding season. 5. The age of the female had a pronounced effect upon the breeding biology, influencing both clutch size and breeding success. The relative age of the male also influenced the date of egg laying in the female. 6. A female which retained her mate from the previous breeding season bred earlier, laid more eggs and had a greater breeding success than one which had paired with a new male. Further, a female which retained the mate from the previous breeding season showed more consistency in time of egg laying. 7. Female kittiwakes which retained the mate of a previous breeding season tended to breed earlier as they gained in breeding experience. Birds breeding with a mate for the first time bred at the same time irrespective of their previous breeding experience. 8. The depressive effect on the breeding biology induced by the change of mate was apparent for at least two breeding seasons after the change took place, the effect being less pronounced in the second year. 9. It is suggested that there is a marked selective value in retaining the same mate from one breeding season to the next, but that in incompatible pairs (which fail to hatch their eggs) their is more advantage in changing mates as by so doing they are more likely to breed successfully.
... As several studies suggest while re-paired individuals may incur short-term costs, divorcing an unsuitable mate in favour of a more compatible one may improve long-term reproductive success (Choudhury, 1995;Wagner et al., 2022). Although divorce is rare in seabirds, when it does occur, it has often been found to follow poor breeding success (Coulson, 1966;Mills, 1973). Mercier et al. (2021) reported that black-legged kittiwakes (Rissa tridactyla, Linnaeus) (henceforth 'kittiwakes') were more likely to remain faithful between years following the successful rearing of a chick. ...
... Individual personality (boldness) is measurable and repeatable in this species and is correlated with foraging strategy, reproductive behaviour and reproductive success (Collins et al., 2019;Harris, Descamps, Sneddon, Cairo, et al., 2020). The idea that kittiwake pairs might rely on behavioural compatibility to coordinate their incubation shifts was posited by Coulson (1966), but empirical evidence is lacking. Evidence suggests that they mate assortatively by boldness, and so personality might provide a viable mechanism by which kittiwakes assess behavioural compatibility during mate choice (Collins et al., 2019). ...
... We predicted that bolder birds would have higher reproductive success but that pairs with greater dissimilarity in their personalities would have lower reproductive success (Biro & Stamps, 2008;Munson et al., 2020) (Figure 1). We also predicted that the probability of re-pairing would increase following breeding failure (Coulson, 1966;Mercier et al., 2021). As a result, we predicted that pairs with greater dissimilarity in personality would be more likely to re-pair. ...
In long‐lived monogamous species, the trigger of costly re‐pairing is not always clear. Limited research suggests that within‐pair behavioural compatibility may be an important driver of partnership success, as cooperation should be enhanced when pair members' decisions complement one another. Animals' decision‐making processes are influenced by personality traits – defined as individual differences in behaviour that are stable in time. Despite the potential for the personality trait ‘boldness’ to (a) directly impact individual willingness to re‐pair and (b) indirectly impact re‐pairing choices via reproductive success, there is currently little work exploring how re‐pairing decisions might be impacted by the pair members' personalities. Using a 13‐year dataset, we investigated whether within‐pair boldness and its relationship with breeding success explained re‐pairing patterns of black‐legged kittiwakes ( Rissa tridactyla ), breeding in two Arctic colonies. We found that pairs with dissimilar boldness levels were more likely to experience breeding failure and that failed pairs were more likely to re‐pair the following year. Despite this, only one colony displayed evidence of assortative mating by boldness, and there was no indication that re‐pairing impacted reproductive success the following season. Neither individual nor pair boldness directly influenced re‐pairing probability; however, in both colonies, re‐pairing birds chose partners that were slightly more similar to themselves in boldness than their previous mates. These results imply an indirect pathway by which poorer behavioural compatibility within pairs may lead to breeding failure and ultimately re‐pairing. Our findings highlight the importance of behavioural compatibility, and possibly personality, in mitigating sexual conflict and its population‐specific drivers.
... [2,3]), while others give reasons why it might be more beneficial to divorce and choose a new partner (e.g. [4,5]). Although many studies have been carried out to answer these questions, a large proportion of them have important limitations [6]. ...
... Individual heterogeneity plays a role here; if all birds have the same breeding capacity the expected gain of changing the mate will be low and might not pay off [8]. It has been suggested that divorce may arise when partners are not well coordinated [4], or more generally as a consequence of a previous wrong partner choice [5], the option of pairing with a higher-quality mate [8] or to avoid inbreeding [9]. By contrast, 'non-adaptive' explanations of divorce state that it arises as a side effect of asynchronous arrival of both partners in the breeding colony [10,11], due to intraspecific competition [12] or as a consequence of external influences leading to temporary loss of the partner [13]. ...
... However, several other studies on a number of bird species have shown that divorce probability is connected to a low breeding success or failure in the previous year (e.g. [3,4,10]). ...
In a monogamous species two partners contribute to the breeding process.We study pair formation as well as the effect of pair bond length and age on breeding performance, incorporating individual heterogeneity, based on a high-quality dataset of a long-lived seabird, the common tern (Sterna hirundo). To handle missing information and model the complicated processes driving reproduction, we use a hierarchical Bayesian model of the steps that lead to the number of fledglings, including processes at the individual and the pair level. The results show that the age of both partners is important for reproductive performance, with similar patterns for both sexes and individual heterogeneity in reproductive performance, but pair bond length is not. The terns are more likely to choose a former partner independent of the previous breeding outcome with that partner, which suggests a tendency to retain the partner chosen at the beginning of the breeding career. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
... A divorce is said to have occurred when two birds that bred together in year t − 1 were alive and present in the colony at year t, but not breeding together. Mate retention occurred when both partners were together at year t − 1 and t, and mate loss occurred when one of the two partners was absent in our study plot (Coulson, 1966;Ens, Safriel & Harris, 1993;Choudhury, 1995). Divorce rate is the number of divorced birds divided by the total number of birds alive. ...
... According to literature reviews written on divorce in monogamous birds (Choudhury, 1995;Culina, Radersma & Sheldon, 2015), our results suggest that divorce is a short-term adaptive strategy to counteract breeding failure occurring when birds are faced with reduced food supplies. Therefore, divorce should be viewed as a reproductive strategy that maximize individual fitness (e.g., Coulson, 1966;Ens, Safriel & Harris, 1993). According to various hypotheses reviewed by Choudhury (1995), it is difficult and hazardous to determine which is the best hypothesis that explains the divorce in a specific bird species. ...
Seabirds exhibit considerable adjustment capacity to cope with environmental changes during the breeding season and to maximize lifetime reproductive output. For example, divorce has been proposed to be an adaptive behavioral strategy in social monogamous species, as a response to poor conditions and low breeding success. Here, we studied divorce at the population and individual levels in northern gannets (Morus bassanus, hereafter gannets) nesting on Bonaventure island (Quebec, Canada). At the population level, we used Granger's method for detecting and quantifying temporal causality between time series (from 2009 to 2019) of divorce rate and breeding success of gannets (n = 809) and we evaluated the relationship between breeding success and biomass of their two principal prey (Atlantic mackerel, Scomber scombrus, and Atlantic herring, Clupea harengus). Our results indicated that breeding success is mainly influenced by the spawning-stock biomass of Atlantic mackerel, and a decrease in breeding success is followed by an increase in divorce rate with a 1-year lag. However, the effect of the interaction between breeding success and year on the proportion of individuals that divorced showed significant inter-annual variation. At the individual level, our results support the adaptive strategy hypothesis of divorce. Indeed, gannets that changed partners did so following a reproductive failure, and there was an increase in breeding success 1 year following the divorce. Being central place foragers, opportunities for dispersal and adaptation are often limited for breeding seabirds in a context of low food abundance. We suggest that behavioral flexibility expressed as divorce would be an efficient short-term strategy for maintaining reproductive performance.
... Studies have shown that mate and nest-site retention are generally high among long-lived seabirds and may be beneficial (Bried and Jouventin 2002). Mating with the same individual may result in better coordination of breeding activities due to familiarity and age or experience and is generally associated with higher reproductive success (Coulson 1966, Williams and Rodwell 1992, Bried and Jouventin 2002. Mate retention also avoids the costs associated with pair formation (Croxall and Davis 1999, Bried andJouventin 2002). ...
... Despite its cost, separation can be adaptive when the cost of retaining an incompatible or inferior mate is high (Bried and Jouventin 2002). According to the ''Incompatibility Hypothesis'', pairs suffer low reproductive success not because one or both partners are of low quality (e.g., low body condition, inefficient foraging, etc), but simply because the combination of their individual traits (behavioral or physiological) are incompatible for successful breeding (e.g., erratic incubation patterns; Coulson 1966, 1972, Johnston and Ryder 1987, Ens et al. 1993. From this hypothesis, both members of the pair would benefit from separation as it would enable them to mate with more compatible partners and increase their reproductive success. ...
Using nest and banding data collected from 1991 to 2002, we investigated mate and territory retention rates of Yellow-eyed Penguins (Megadyptes antipodes), and the effects of reproductive success. Annual mate retention rate was 63%, and territory retention for males and females were 52% and 46% respectively. The majority of pair dissolutions were due to death of a partner, with only 6% of bonds ending in separation. Previous reproductive success was a good predictor of mate or territory retention as pairs that failed to fledge a single chick were significantly more likely to separate or move their territories than those that were successful at fledging chicks. Reproductive success of birds that changed their mates or moved territories was not higher than those that retained their mates or territories. However, birds that moved territories were less likely to have reduced fledging success relative to their previous breeding attempt. Birds that did not retain their mates, particularly males, were significantly more likely to skip breeding for at least one year. This suggests that the costs of mate or territory changes are not accrued at the end of the breeding attempt (as reflected by the number of fledged chicks), but are associated with the costs of pair formation and establishment of territories at the beginning of the breeding season.
Retención de Parejas y Territorios en Pingüinos Megadyptes antipodes
Resumen. Investigamos las tasas de retención de parejas y de territorios por parte de pingüinos Megadyptes antipodes y el efecto del éxito reproductivo sobre estas tasas con base en datos de nidificación y anillamiento recolectados entre 1991 y 2002. La tasa anual de retención de parejas fue del 63% y las de retención de territorios del 52% y 46% para machos y hembras, respectivamente. La mayoría de las disoluciones de parejas se debieron a la muerte de una de las aves y sólo el 6% de las parejas terminaron separándose. El éxito reproductivo previo predijo acertadamente la retención de compañeros y de territorios, ya que las parejas que no lograron emplumar ningún pichón tuvieron una probablilidad de disolverse o de cambiar de territorio significativamente mayor que las que criaron exitosamente. El éxito reproductivo de las aves que cambiaron de pareja o de territorio no fue mayor que el de aquellas que no lo hicieron. Sin embargo, los individuos que cambiaron de territorio fueron más propensos a presentar un éxito de emplumamiento reducido con respecto a su intento reproductivo previo. Las aves que no retuvieron sus parejas, particularmente los machos, presentaron una probabilidad mayor de no reproducirse durante al menos un año. Esto sugiere que los costos que implica cambiar de pareja o de territorio no se hacen evidentes al final del intento reproductivo (como lo indica el número de volantones producidos), sino que están asociados con los costos de la formación de parejas y el establecimiento de territorios al comienzo de la época reproductiva.
... Adult survival is the most important factor influencing population growth rates and growth may be further complicated by the fact that not all pairs contributed equally to the next generation [54,55]. The successful brooding of eggs through to fledging is influenced by a range of factors, including mate quality, age, and the experience of the pair, and reproductive success is typically higher among older, more experienced pairs than younger birds [54,[56][57][58]. Therefore, the loss of experienced, high-quality birds from the population is likely to have a negative effect on population growth in the longer-term. ...
... Surveys have shown that approximately 60% of Australian cat owners accept that pet cats killing wildlife in cities, towns and rural areas is a problem [71], which gives some basis to encourage wildlife-friendly cat husbandry. However, it may be even more effective to highlight to owners the cat welfare benefits that arise when cats are kept on their owner's property at all times e.g., [56]. With regard to semi-feral cats, some Australians and citizens of other countries, such as the USA, support or practice trap-neuter-release (TNR), in which semi-feral cats are trapped, desexed, and then returned to the environment as a humane response to cat overpopulation [21,72,73]. ...
Simple Summary
Feral cats living completely independently of people are, unequivocally, agents of wildlife decline, which is linked to the local extinction of numerous bird, mammal and reptile species worldwide. However, evidence of the impact of pet and semi-feral (stray) cats on wildlife is somewhat limited, possibly due to the rapidity with which predation events occur. This study highlights the impact of a semi-feral cat on a threatened seabird colony of Australian Fairy Terns, Sternula nereis nereis, in Mandurah, south-western Australia. Evidence for significant predator-induced mortality, the alteration of the natural behavior of nesting birds in response to a persistent predator, and the complete reproductive failure of 111 nests—due, largely, to predation by a single, desexed, semi-feral cat—is presented. Trap-neuter-release was proposed as a humane response to tackle cat overpopulation but it fails to address the recurrent depredations on native wildlife that occur post-release. This case-study demonstrates that desexed, free-roaming cats remain a significant threat to wildlife and can lead to swift population declines and the local extirpation of native species.
Abstract
Domestic cats have a cosmopolitan distribution, commonly residing in urban, suburban and peri-urban environments that are also critical for biodiversity conservation. This study describes the impact of a desexed, free-roaming cat on the behavior of a threatened coastal seabird, the Australian Fairy Tern, Sternula nereis nereis, in Mandurah, south-western Australia. Wildlife cameras and direct observations of cat incursions into the tern colony at night, decapitated carcasses of adult terns, dead, injured or missing tern chicks, and cat tracks and scats around the colony provided strong evidence of cat predation, which led to an initial change in nesting behavior and, ultimately, colony abandonment and the reproductive failure of 111 nests. The death of six breeding terns from the population was a considerable loss for this threatened species and had the potential to limit population growth. This study highlights the significant negative impacts of free-roaming cats on wildlife and the need for monitoring and controlling cats at sites managed for species conservation. It also provides strong evidence against the practice of trap-neuter-release programs and demonstrates that desexed cats can continue to negatively impact wildlife post-release directly through predation, but also indirectly through fundamental changes in prey behavior and a reduction in parental care.
... Secondly, nest desertion likely reduces nest detection by potential predators, which increases the chances of reproductive success, particularly for early-and mid-season nesters (Coulson 1966, Atwood 1986. Each breeding attempt is energetically costly, and birds breeding earlier in the season (closer to peak food availability) are typically more successful than those that lay later or birds laying for the second time (Coulson 1966). ...
... Secondly, nest desertion likely reduces nest detection by potential predators, which increases the chances of reproductive success, particularly for early-and mid-season nesters (Coulson 1966, Atwood 1986. Each breeding attempt is energetically costly, and birds breeding earlier in the season (closer to peak food availability) are typically more successful than those that lay later or birds laying for the second time (Coulson 1966). Therefore, reducing colony detectability, as opposed to completely abandoning the colony site, may be a strategy used to enhance reproductive success (Safina & Burger 1983). ...
This study describes nest desertion as a probable but previously undescribed anti-predator strategy for the Australian Fairy Tern Sternula nereis nereis. Deserted nests were observed at night for up to nine nights following the laying of the first eggs at a colony in southwestern Australia. Nocturnal nest desertion may provide the terns with a mechanism for assessing the occurrence of potential nest predators, maintaining reproductive synchrony, and reducing the total time a colony is detectable by predators. Additionally, temporary diurnal nest desertion for up to 80 minutes was observed following the predation of an adult tern. Diurnal nest desertion may be used to reduce the risk of adult mortality and, consequently, decrease colony visibility, thereby increasing reproductive success.
... Several hypotheses may explain why and when divorce occurs between monogamous partners. Among the most studied: (i) the 'incompatibility hypothesis' predicts that incompatible partners (i.e., for behavioural and or morphological traits) will jointly engage in divorce when facing reduced breeding success (Coulson 1966(Coulson , 1972; (ii) and the 'better option hypothesis' states that divorce can be expected when the benefits of the separation outweigh the costs associated with mate-switching and new partner research processes . Indeed, divorce often follows breeding failures (Brooke 1978;Dhondt and Adriaensen 1994;Choudhury 1995;Desrochers and Magrath 1996;Culina et al. 2015), and is often correlated with an increase in breeding success when it leads to the formation of a new pair (Culina et al. 2015). ...
... As a consequence, long-term pairing species like rooks or jackdaws are often assumed to pair up for life. However, although rare in occurrence, divorce can still be expected under certain circumstances in longterm pairing species (e.g., repeated breeding failures following the incompatibility hypothesis, Coulson 1966;1972;and/or new partnership opportunities following the better option hypothesis, Ens et al. 1993). This applies in particular to species living in group all year long, like rooks, thus in a social surrounding providing consistent and abundant partners opportunities, and where withering relationships are more likely to succumb to this temptation. ...
In birds, long-term pairing often comes with increased breeding success, but also with strong and intricate relationships associated with social benefits, resulting in a lower likelihood of divorce. However, a relationship may wither and the temptation of new partnership opportunities can lead to divorces and re-pairing, especially in social species, like rooks, who live all year round in colonies. Here, we scrutinized the behavioural patterns leading to divorce and pair formation by adulthood in a group of captive rooks. Divorces were concomitant to the formation of new pairs, with one or both separating partners gradually switching to another relationship. Individuals switching from one pair to another were socially less active than their non-switching partner (the old and new). Once established, newly formed pairs were immediately as strong as older stable pairs. Separating pairs were characterized by high rates of agonistic behaviours. Food sharing played a role in the formation of new pairs, while sexual behaviours did not. We showed that adult rooks do not necessarily pair for life, and have the ability to strongly re-bond with another partner. This emphasizes the social flexibility of this cognitively advanced species, and sheds new light on mate choice strategies in long-term monogamous species.
... This was made of a specially formulated polymer ("Darvic") produced by Imperial Chemical Industries in the United Kingdom which is exceptionally durable and colour-fast. The material had originally been put to use as a bird band by Coulson in his seminal studies of the Black-legged Kittiwake (Rissa tridactyla) at North Shields, UK (Coulson 1966). At Coats, one colour (light green) was reserved for birds banded as adults. ...
The Coats Island field station in northern Hudson Bay, Canada, was established by the Canadian Wildlife Service in 1984 to monitor the thick-billed murre (Uria lomvia, akpa, ) population in the context of harvest management and federal responsibilities under the Migratory Birds Convention Act. The long-term monitoring program has continued annually for 34 of the last 39 years, making it the most frequently monitored seabird colony in the Canadian Arctic. In the 1990s, the focus of efforts at the site shifted from population monitoring and harvest management to long-term monitoring of murres as an indicator of environmental change. In addition to informing harvest management of murres in Canada, long-term monitoring and research at Coats Island have helped to establish thick-billed murres as an indicator species for Arctic seabirds, identified major shifts in the marine prey communities of Hudson Bay, enabled the assessment of international agreements on reducing contaminants in Arctic wildlife, and improved the understanding of the effects of climate change on Arctic marine birds. Coats Island has developed into an essential research site for all aspects of murre ecology and served as a training site for new generations of Arctic ecologists.
... Hypothesis 3: mate change is costly for short-term reproductive success. Previous work has shown that mate change is detrimental to short-term fitness in seabirds (e.g. in short-tailed shearwaters, Puffinus tenuirostris, Bradley et al., 1990;in barnacle geese, Branta leucopsis, Forslund & Larsson, 1991; in Australasian gannets, Morus serrator, Ismar et al., 2010;and in Scopoli's shearwaters, Thibault, 1994), especially in the first year following a mate change (in Manx shearwaters, Puffinus puffinus, Brooke, 1978; in kittiwake gulls, Rissa tridactyla, Coulson, 1966; in arctic skuas, Stercorarius parasiticus Davis, 1976; and in fulmars, Fulmarus glacialis, Ollason & Dunnet, 1988). Based on this hypothesis, we expected that the probability of breeding success would decrease after a mate change occurs. ...
Keywords: fitness mate change pair bond skipping breeding social monogamy survival Social monogamy is the most common social mating system in birds. However, the persistence of pair bonds between breeding seasons varies among species, populations and individuals. Understanding fitness causes and consequences of mate change is critical for understanding population dynamics and the evolution of social monogamy. We used 12 years of data from Scopoli's shearwater breeding population to estimate mate change probabilities and test whether they affect the probabilities of (1) skipping breeding, (2) apparent survival and (3) breeding success. Widowing was the most common cause of mate change, with more males changing mates at least once in their lives than females. Females' probability of skipping a breeding season increased significantly just before pairing with a new partner. Also, we found that females' apparent survival, but not males', might increase after mate change. A possible explanation is that a longer adult life expectancy of females after mate change could at least partially offset the cost of skipping breeding. We found no relation between mate change and breeding success. Our study suggests that the costs and benefits of mate fidelity may be sex specific in this species. Future research on this topic should focus on the effects of mate change on each sex's lifetime reproductive success, which we could not address specifically in this study. Future studies will hopefully be able to delve deeper into how mate change, caused by divorce or widowhood, shifts the balance of reproduction or survival, determining lifetime reproductive success.
... A divorce is said to have occurred when two birds that bred together in year t-l are alive and present in the colony in year t , but not breeding together. Mate loss occurred when one partner is absent in our study plot (Coulson, 1966;Harris et al., 1987;Ens et al., 1993;Choudhury, 1995). We used the same dataset of partnership status as Pelletier and Guillemette (2022) in which they monitored a total of 809 birds from 2008 to 2019. ...
Decreased productivity in long-lived bird species is linked to prey depletion in marine ecosystems. Seabirds, however, exhibit behavioral flexibility at individual level to prevent this outcome. One such strategy to alleviate any impact on fitness would be to divorce from their partners. Although changing mates and increasing foraging effort have been shown to increase or maintain reproductive success, how the behavioral flexibility affects fundamental physiological parameters remains to be elucidated. Here, we compared physiological components (nutritional status, muscle damage and oxidative stress) of northern gannets (Morus bassanus) in relation to their partnership status and foraging effort. Specifically, we used a cross-sectional data set (at the population level) of three contrasted years to compare retained and changed mates. We predicted that mate change is a stressful event with impacts on health condition and those effects are higher during unfavorable years with food depletion. Our study showed that gannets changing mate increase parental effort only during years of low food abundance, with consequences on health condition (increased body mass loss, higher protein catabolism and higher oxidative damage during chick rearing period). Ultimately, our study suggests that partnership decision is not likely to reduce the long-term quality and the fitness of parents. Reproduction during harsh conditions would however likely be one of the primary causes of individual quality loss and fitness decline in this long-lived bird species.
... However, in species where both partners invest in a clutch, not only individual behaviour, but also the behaviour of the partner and the emergent traits of the pair bond can affect reproductive success. Thus, the similarity of defensive behaviour between partners may affect reproductive success, since the coordination of behaviour between partners within a breeding pair may be more important for clutch survival than the overall investment in clutch defence (Coulson 1966, Spoon et al. 2006, Schuett et al. 2011, Burtka and Grindstaff 2015. If behavioural similarity exists in a species, it could have evolved as a result of selective advantages in reproductive success. ...
Behavioural patterns often differ consistently across individuals and are linked to fitness. In species with biparental care, the defence behaviour of both parents can affect reproductive success through offspring survival. In addition to the intensity of defence behaviour by both pair members, the similarity in this behaviour among parents may affect offspring survival. However, few studies have investigated the relative impact of both the intensity and similarity of defence behaviour. Here, we examined nest defence behaviour of males and females during the incubation stage in an Arctic population of barnacle geese Branta leucopsis. We calculated the repeatability of defence behaviour to test whether this behaviour is consistent within individuals and investigated how it is associated with age. In addition, we investigated how daily survival rate (DSR) of the nests until hatching is associated with nest defence behaviour and age of the parents, as well as the effect of parent similarity in nest defence behaviour as an emergent trait of the pair bond. Both male and female defence behaviour were highly repeatable. The ages of both partners within breeding pairs were positively related, but age was only significantly associated with defence behaviour in females. Further, we found high similarity in defence behaviour within breeding pairs, but the similarity and intensity of defence behaviour within breeding pairs did not predict DSR. Finally, male defence behaviour positively predicted DSR, but female defence behaviour and male and female age did not. Our results suggest that nest protection is adaptive in males but behavioural similarity of pair members does not enhance nest survival, indicating behavioural similarity itself is not adaptive but rather a by‐product of different effects.
... For instance, alloparental care appears to have evolved in some species to provide opportunities to practice raising offspring, thereby benefitting future offspring of the now experienced, and presumably competent, parents [25,26]. Indeed, practice via alloparental care increases offspring survival in many species, including primates [26][27][28][29], birds [30][31][32][33], and rodents [34][35][36]. For example, male Mongolian gerbils (Meriones unguiculates) with alloparental experience produce their first litter sooner, and their pups gain weight faster than litters from alloparentally inexperienced males [35]. ...
Parental care is critical for offspring survival in altricial species. Although parents are the most common caregivers, other individuals (e.g., older siblings) can also provide alloparental care. Some have argued that animals engage in alloparental behavior to practice providing care for their eventual offspring, whereas others have argued that alloparental behavior enhances indirect fitness. Proximate measures have the potential to test ultimate functions of behavior. A focus on neural expression of oxytocin and vasopressin (two neuropeptides modulating alloparental care) or neural activation following exposure to related and unrelated individuals could reveal whether practice or investment in indirect fitness explains alloparental behavior. This study examined alloparental behaviors and neural responses in prairie voles (Microtus ochrogaster), a species that engages in alloparental behavior. Subadult (independent, yet sexually immature) male prairie voles were exposed to one of four stimuli: same-age sibling, neonatal sibling, unrelated neonate, or inanimate neonate-sized object. We assessed alloparental behaviors and quantified cFos protein expression in oxytocin and vasopressin neuronal populations of the paraventricular nucleus of the hypothalamus and the supraoptic nucleus of the hypothalamus in response to stimulus exposure. We detected no differences in cFos and nonapeptide co-localization among stimulus groups. Subjects performed similar amounts of alloparental care toward related and unrelated neonates, but not other subadults or inanimate objects. Notably, caregiving did not differ based on kin-status. The lack of difference in alloparenting toward related and non-related neonates suggests that alloparental care in prairie voles primarily serves to provide subadults with parental practice.
... For birds, the term "divorce" has been used to describe a change of breeding partner when both partners are still alive; this contrasts to "widowing" when one of the partners has died (Culina et al., 2015). Divorce could be an adaptive strategy if an individual expects to get a better quality mate (the better option hypothesis: Baeyens, 1981;Ens et al., 1993) or a more compatible one (i.e., a mate with characteristics that combined with those of that individual will enhance their fitness; the incompatibility hypothesis: Coulson, 1966;Dubois and Cézilly, 2002). Alternatively, the change may be forced on the individual, for example as a result of intra-sexual competition (e.g., nest usurpation) or as a consequence of a low probability of reencountering a mate (Culina et al., 2015). ...
Variation in avian reproductive strategies is often studied from a comparative perspective, since even closely-related taxa differ greatly in the degree of polygyny, extra-pair paternity (EPP) or intra-specific brood-parasitism. However, substantial variation at the species level suggests that ecological factors are important in shaping these patterns. In this study, we examined the temporal plasticity of these strategies, following a population from the year of colony formation to 2 years after this. Parentage data from these years shows that polygyny decreased with time, likely as a consequence of increased competition for nesting sites and mates by new recruits, and immigrants of higher quality arriving to the colony as time passed. In parallel to this temporal change, we found an increase in intra-specific brood-parasitism and quasi-parasitism (QP). We interpret these patterns as a consequence of an increase of floaters with time; these birds pursue a mixture of alternative mating strategies to succeed in the population. We also found evidence of conspecific brood parasitism (CBP), by nesting females that laid part of the clutch in another nest or that after losing a partially laid clutch resorted to lay the last eggs in another nest. Analyses of the distance between the main nest and nests containing the secondary polygynous brood or extra-pair or parasitic young showed an avoidance of contiguous nests for conducting these alternative reproductive tactics. At the same time, these secondary nests were closer to the main nest than random distances within the colony, suggesting that access to public information was restricted to a narrow area around the main nest. Our study emphasizes how behavioral patterns are plastic traits that vary not only with individual circumstances, but also with time, tracking changes in density and social structure.
... The "mate familiarity hypothesis" highlights that retaining a mate could improve breeding performance by enhancing coordination between parents and thereby improving reproductive success 13,34,35 . In contrast, changing a mate may be beneficial in some long-lived species, as individuals may divorce their current partner to mate with relatively higher quality or more compatible partners in order to improve breeding success ("incompatibility hypothesis" 36 ; also see 37 ); as a corollary, successful breeding pairs are more likely to stay together for future breeding attempts 11,38,39 . It has also been suggested that divorcing and rapidly changing a mate may be favoured by some species in order to make the most out of a restricted time budget (e.g. ...
When individuals breed more than once, parents are faced with the choice of whether to re-mate with their old partner or divorce and select a new mate. evolutionary theory predicts that, following successful reproduction with a given partner, that partner should be retained for future reproduction. However, recent work in a polygamous bird, has instead indicated that successful parents divorced more often than failed breeders (Halimubieke et al. in Ecol Evol 9:10734-10745, 2019), because one parent can benefit by mating with a new partner and reproducing shortly after divorce. Here we investigate whether successful breeding predicts divorce using data from 14 well-monitored populations of plovers (Charadrius spp.). We show that successful nesting leads to divorce, whereas nest failure leads to retention of the mate for follow-up breeding. plovers that divorced their partners and simultaneously deserted their broods produced more offspring within a season than parents that retained their mate. our work provides a counterpoint to theoretical expectations that divorce is triggered by low reproductive success, and supports adaptive explanations of divorce as a strategy to improve individual reproductive success. in addition, we show that temperature may modulate these costs and benefits, and contribute to dynamic variation in patterns of divorce across plover breeding systems. open
... In populations of (partially) migratory species, it has been shown that individuals mate assortatively based on their arrival time in the breeding area (Bearhop et al., 2005;Village, 1985; see also Lozano et al., 1996) which may also be linked to agedependent arrival (Coulson, 1966). Moreover, a recent study on great tits found that individuals associated with one another assortatively depending on their arrival time in the non-breeding season (Farine & Sheldon, 2015). ...
Events in one part of the annual cycle often affect the performance (and subsequently fitness) of individuals later in the season (carry‐over effects). An important aspect of this relates to the timing of activities. For example, many studies on migratory birds have shown that relatively late‐spring arrival in the breeding area reduces both the likelihood of getting a mate or territory and reproductive success.
In contrast, relatively little is known about the movements of individuals in non‐migratory populations during the non‐breeding season. Few studies have investigated the timing of arrival at the breeding area in such species, possibly due to the assumption that most individuals remain in the area during the non‐breeding season.
In this study, we used 4 years of data from a transponder‐based automated recording system set up in a non‐migratory population of blue tits Cyanistes caeruleus to describe individual variation in arrival at the breeding site. We investigated whether this variation can be explained by individual characteristics (sex, body size or status), and we assessed its effect on aspects of reproductive success in the subsequent breeding season.
We found substantial variation in arrival date and demonstrate that this trait is individual‐specific (repeatable). Females arrived later than males, but the arrival dates of social pair members were more similar than expected by chance, which suggests that individuals may mate assortatively depending on their arrival in the breeding area. Arrival predicted both whether an individual would end up breeding that season and several aspects of its breeding success.
Our study suggests that individuals of non‐migratory species leave the breeding area during the non‐breeding season. Hence, it may be useful to consider variation in the scale of movements between breeding and non‐breeding sites, rather than using a simple dichotomy between ‘resident’ and ‘migratory’ species. We conclude that the timing of pre‐breeding events, in particular arrival date, may be an overlooked, but important, fitness‐relevant trait in non‐migratory species.
... Perhaps the improved hatching success for older males occurs because they are more responsive to their partner's absences and coordinate incubation switches more closely so the eggs do not chill when left unattended. Similarly, experience improved hatching success in kittiwakes Rissa tridactyla (Coulson 1966) and compatibility between partners improved hatching in cockatiels Nymphicus hollandicus (Spoon et al. 2006), suggesting attentiveness and coordination is important for biparental incubators. ...
Age-related improvement in reproductive performance is widespread in vertebrates and constraints at young ages are a common cause. The sex that invests energetically more in reproduction, typically the female, is predicted to show stronger age-related performance but the effect of the male’s age on reproduction has often been ignored. I studied age-related reproduction of both sexes in northern flickers, in which males invest more parental care than females, predicting that the effect of age would be stronger in males than in females. Longitudinal data on individuals collected during an 18-year field study confirmed this prediction. Laying dates for females improved only between the first 2 years of her life and no other reproductive parameter changed over her lifetime when the male’s age was statistically controlled. In contrast, males improved up to age five for laying date, clutch size, hatching success and fledging success. Partner familiarity (fidelity) was further associated with earlier laying, larger clutches, improved fledging success and more fledglings. There was significant assortative pairing by age but there is apparently little benefit for males to choose older females, but a benefit to females with older males. Females appear to strategically lay larger clutches when paired to old males which invest more in paternal care than younger males. This is the first example of clutch size being influenced by only male age and not female age in any bird and suggests that sex roles in parental care are important determinants of aging patterns in vertebrates with diverse life histories.
... Until recently, only the Atlantic subspecies (R_. ~. tridactyla) had been studied in substantial detail, with most effort focusing on populations in the British Isles: Coulson and White (1956, 1958a, 1958b, 1959, 1960, Coulson (1963Coulson ( , 1966Coulson ( , 1968, and Wooller (1976, 1977). Information from the western Atlantic is based on one intensive study of breeding biology in Newfoundland by Maunder and Threlfall (1972 1976 1976 1977 1978 1976 1977 1977 1978 1977 1978 1977 1978 1978 1976-77 Leschner and Burrell (1977) Hatch (1978) Hatch and Hatch (1979) Wehle et al. (1977) Wehle (1978) Baird and Moe (1978) Nysewander and Hoberg (1978) Manuwal and Boersma (1978a) Manuwal and Boersma (1978b) Jones and Petersen (1979) Hinchinbrook 1976 1976 1976 1977 1978 1975 1977 1978 1975 1977 1978 1978 1972 1975 1976 1977 1972 1976 1977 1978 1956 . ...
Research over four years on breeding biology, feeding ecology, abundance and distribution of ten species seabirds in seven colonies
... Monogamy in birds represents a partnership in which the female and male adjust their behaviour to each other and synchronize many of their activities (Black, 1996). Many long-term monogamous species show an increase in reproductive success with pair bond duration, which may be due to the improvement in partners' coordination over time (mate familiarity effect, Black, 2001;Coulson, 1966;Forslund & P€ art, 1995). In some species, partners synchronize their foraging trips or their nest visits to feed the chicks (Lee, Kim, & Hatchwell, 2010;Van Rooij & Griffith, 2013), and their degree of synchrony can correlate with their reproductive success (Mariette & Griffith, 2012. ...
The coordination of behaviours between mates is a central aspect of the biology of the monogamous pair bonding in birds. This coordination may rely on intrapair acoustic communication, which is surprisingly poorly understood. Here we examined the impact of an increased level of background noise on intrapair acoustic communication at the nest in the zebra finch, Taeniopygia guttata. We monitored how partners adapted their acoustic interactions in response to a playback of wind noise inside the nestbox during incubation. Both zebra finch parents incubate and use coordinated call duets when they meet at the nest. The incubating parent can vocalize to its partner either outside the nestbox (sentinel duets) or inside the nestbox (relief and visit duets), depending on the context of the meeting. Pairs use these duets to communicate on predation threats (sentinel duets), incubation duties (relief) and other nesting activities (visit duets). Each of these duets probably represents a critical component of pair coordination. In response to the noise playback, partners called less and more rapidly during visit and relief duets. Female and male calls were more regularly and precisely alternated during relief duets. Mates increased the number of visit duets and their spatial proximity during sentinel duets. Furthermore, both females and males produced louder, higher-frequency and less broadband calls. Taken together our results show that birds use several strategies to adjust to noise during incubation, underlining the importance of effective intrapair communication for breeding pairs.
... Our data suggest that spotted owls were more likely to undertake breeding dispersal if (1) they were female, (2) they were young, (3) they did not nest in the previous year, (4) they did not have a mate in the previous year, or (5) their mate from the previous year died or moved to a new territory. These results generally agree with other studies of birds that have shown that rates of breeding dispersal were higher for females, young birds, birds that lost a mate through death or divorce, or birds that failed at nesting (Coulson 1966, Newton and Marquiss 1982, Greenwood and Harvey 1982, Greig-Smith 1982, Bowen et al. 1989, Taylor 1994, Wellicome et al. 1997, Marti 1999, Daniels and Walters 2000. One hypothesis for higher rates of female breeding dispersal is that, in a ter-ritorial defense system in which the male locates and defends the territory, it may be more difficult for males to switch territories than it is for females to switch mates (Emlen andOring 1977, Greenwood andHarvey 1982). ...
We studied the dispersal behavior of 1,475 northern spotted owls (Strix occidentalis caurina) during banding and radio-telemetry studies in Oregon and Washington in 1985-1996. The sample included 324 radio-marked juveniles and 1,151 banded individuals (711 juveniles, 440 non-juveniles) that were recaptured or resighted after dispersing from the initial banding location. Juveniles typically left the nest during the last week in May and the first two weeks in June (x̄ ± SE = 8 June ± 0.53 days, n = 320, range = 15 May-1 July), and spent an average of 103.7 days in the natal territory after leaving the nest (SE = 0.986 days, n = 137, range = 76-147 days). The estimated mean date that juveniles began to disperse was 19 September in Oregon (95% CI = 17-21 September) and 30 September in Washington (95% CI = 25 September-4 October). Mean dispersal dates did not differ between males and females or among years. Siblings dispersed independently. Dispersal was typically initiated with a series of rapid movements away from the natal site during the first few days or weeks of dispersal. Thereafter, most juveniles settled into temporary home ranges in late October or November and remained there for several months. In February-April there was a second pulse of dispersal activity, with many owls moving considerable distances before settling again in their second summer. Subsequent dispersal patterns were highly variable, with some individuals settling permanently in their second summer and others occupying a series of temporary home ranges before eventually settling on territories when they were 2-5 years old. Final dispersal distances ranged from 0.6-111.2 km for banded juveniles and 1.8-103.5 km for radio-marked juveniles. The distribution of dispersal distances was strongly skewed towards shorter distances, with only 8.7% of individuals dispersing more than 50 km. Median natal dispersal distances were 14.6 km for banded males, 13.5 km for radio-marked males, 24.5 km for banded females, and 22.9 km for radio-marked females. On average, banded males and females settled within 4.2 and 7.0 territory widths of their natal sites, respectively. Maximum and final dispersal distances were largely independent of the number of days that juveniles were tracked. Although statistical tests of dispersal direction based on all owls indicated that direction of natal dispersal was non-random, the mean angular deviations and 95% CI's associated with the samples were large, and r-values (vector length) were small. This lead us to conclude that significant test results were the result of large sample size and were not biologically meaningful. Our samples were not large enough to test whether dispersal direction from individual territories was random. In the sample of radio-marked owls, 22% of males and 44% of females were paired at 1 year of age, but only 1.5% of males and 1.6% of females were actually breeding at 1 year of age. At 2 years of age, 68% of males and 77% of females were paired, but only 5.4% of males and 2.6% of females were breeding. In contrast to the radio-marked owls, most juveniles that were banded and relocated at 1 or 2 years of age were paired, although few were breeding. Although recruitment into the territorial population typically occurred when owls were 1-5 years old, 9% of banded juveniles were not recaptured until they were > 5 years old. We suspect that our estimates of age at recruitment of banded owls are biased high because of the likelihood that some individuals were not recaptured in the first year that they entered the territorial population. A minimum of 6% of the banded, non-juvenile owls on our demographic study areas changed territories each year (breeding dispersal). The likelihood of breeding dispersal was higher for females, young owls, owls that did not have a mate in the previous year, and owls that lost their mate from the previous year through death or divorce. Mean and median distances dispersed by adults were shorter than for juveniles, and did not differ between the sexes or study areas (x̄ = 6.1 km, median = 3.5 km). Owls that were 1-2 years old tended to disperse farther than owls that were > 2 years old. The direction of post-natal dispersal did not differ from random. The large nonforested valleys of western Oregon (Willamette, Umpqua, Rogue Valleys) acted as barriers to dispersal between the Coast Ranges and the Cascade Mountains. However, dispersal did occur between the Coast Ranges and Cascade Mountains in the forested foothills between the non-forested valleys. Forest landscapes traversed by dispersing owls typically included a fragmented mosaic of roads, clear-cuts, non-forest areas, and a variety of forest age classes ranging from young forests on cutover areas, to old-growth forests ≥ 250 years old. Our data fit the general pattern observed in birds in that females dispersed farther than males and dispersal distances were negatively skewed towards short distance dispersers. Comparison of data from radio-marked and banded owls demonstrated that the negatively skewed distribution of dispersal distances represented the actual distribution of dispersal distances, and was not the result of small study area bias on recaptures. We found no correlation between dispersal distance and age at first breeding, which suggests that reproductive fitness is not affected by dispersal distance. We observed only 3 cases of close inbreeding (parent-offspring or sibling pairs) in thousands of pairs of spotted owls, suggesting that dispersal results in a very low incidence of close inbreeding in the spotted owl. However, inbreeding with more distant relatives was common.
Despite the advantages of lasting pair bonds and the prevalence of monogamy, at least in avian species, some individuals switch mates (divorce). Divorce is generally considered to be adaptive (i.e., conferring net fitness benefits), although its causes and consequences often remain unclear, most notably regarding the genetic basis of this behavior. Using more than 30 years of data in a long-lived bird with obligate biparental care, the Alpine swift, we first described the overall patterns of mate and nest site fidelity and investigated the predictors of between-year divorce. We show that 16.6% of pairings ended in divorce, with low reproductive success and young age as predictors of divorce, and that males retained the nest site more often than females. By then studying individual repeatability and heritability of divorce, we show moderate repeatability in females and low repeatability in males and little additive genetic variance in either sex. Finally, we assessed the fitness consequences of divorce and report that an active decision to modify the pair bond (divorce) may be more beneficial than reactionary re-pairing following a partner's death. Overall, divorce may provide some reproductive benefits for Alpine swifts, but no microevolutionary potential of this behavior is evident in this population.
The age of individuals has consequences not only for their fitness and behaviour but also for the functioning of the groups they form. Because social behaviour often changes with age, population age structure is expected to shape the social organization, the social environments individuals experience and the operation of social processes within populations. Although research has explored changes in individual social behaviour with age, particularly in controlled settings, there is limited understanding of how age structure governs sociality in wild populations. Here, we synthesize previous research into age-related effects on social processes in natural populations, and discuss the links between age structure, sociality and ecology, specifically focusing on how population age structure might influence social structure and functioning. We highlight the potential for using empirical data from natural populations in combination with social network approaches to uncover pathways linking individual social ageing, population age structure and societal functioning. We discuss the broader implications of these insights for understanding the social impacts of anthropogenic effects on animal population demography and for building a deeper understanding of societal ageing in general.
This article is part of the discussion meeting issue ‘Understanding age and society using natural populations’.
Whether natural selection leads to attachment in monogamous pair bonds has seldom been addressed. Operationally defining attachment as a behavioral modifier that decreases divorce probability with pair duration, we develop a model for the evolution of attachment. If divorce (the ending of a pair bond when both individuals survive to the next breeding season) is more likely to occur out of poor-quality reproductive opportunities (i.e., poor territory or low-quality mate), individuals in experienced pairs are more likely to be found in high-quality opportunities. Consequently, when divorce decisions occur using imperfect information from reproductive success, pair duration provides individuals with information about the quality of their reproductive opportunity and attachment can evolve. We show that high survival rates, divorce propensities, and probabilities of nest failure favor the evolution of attachment. Attachment is also more likely to evolve when individuals can directly assess the quality of their reproductive opportunity (as opposed to relying on imperfect information from reproductive success), when the quality of the reproductive opportunity has adult survival ramifications, and when divorce coevolves with attachment. We show that our core conclusions are robust to a variety of assumptions using individual-based simulations. Our results clarify how attachment can be adaptive and suggest that studying pair bonds as dynamic entities is a promising avenue for future work.
The ways by which male and female birds locate and choose each other for mating, the number of mates during a breeding season and during a bird’s life, the duration of interactions between males and females, and the respective roles of males and females in providing care (or not) for eggs and young after fertilization vary among species and, to a lesser extent, within species. The different ways that birds of different species interact to produce young are referred to as mating systems. In this chapter, I discuss the various mating systems of birds, including monogamy, polygyny, polyandry, polygynandry, and promiscuity, and explain the factors that have likely contributed to their evolution. Also in this chapter is a discussion of sexual conflict and cooperation, and factors that contribute to variation among and within species in extra-pair mating. Some species of birds breed cooperatively and the social and environmental variables that contribute to such behavior are discussed. The choice of a mate is critical for birds attempting to maximize their reproductive fitness, and both female and male mate choice and the role of sexual selection in mate choice are discussed in detail.
Divorce among serially monogamous birds can lead to increased reproductive success if an individual obtains a higher-quality mate or nest site, or it can lead to lower reproductive success due to lack of pair experience or reduced breeding opportunities. Identifying the drivers and consequences of mate retention and divorce are necessary then to understand population dynamics, particularly as animals may alter behaviours in response to climate-induced environmental changes. We used a 33-year data set from a declining Magellanic penguin, Spheniscus magellanicus, colony to identify drivers of mate retention and divorce and test whether the nature of those drivers differed between first-year and long-term pairs. In a pair's first year, breeding outcome was the most important predictor of whether mates would reunite: failure rates were high and 71% of first-year pairs divorced on the whole, but only 47% of pairs that fledged a chick divorced. For long-term pairs, both breeding outcome and between-season changes to nest quality were the most important predictors of whether a pair stayed together: pairs that had a chick hatch or fledge divorced at lower rates than those that failed at the egg stage, and pairs whose nest quality declined were more likely to divorce. We also examined the fitness consequences of divorce by comparing the rates at which females and males obtained new mates and fledged chicks in the following year. Although females were more likely than males to secure a new mate, both sexes experienced similarly increased reproductive success with their new mates compared to their old mates, showing that divorce is adaptive.
Despite widespread interest in the evolution and implications of monogamy across taxa, less attention—especially theoret-ical—has been paid toward understanding the evolution of divorce (ending a socially monogamous pairing to find a new partner). Here, we develop a model of the evolution of divorce by females in a heterogeneous environment, where females assess territory quality as a result of their breeding success. Divorce results in females leaving poor territories disproportionally more often than good territories, while death of a partner occurs independent of territory quality, giving an advantage to divorce. Increasing environmental heterogeneity, a decreasing benefit of pair experience, and moderate survival rates favor the evolution of higher divorce rates, even in the absence of variance in individual quality and knowledge of available territories. Imperfect information about territory quality constrains the evolution of divorce, typically favoring divorce strategies that remain faithful to one’s partner whenever successful reproduction occurs. Our model shows how feedbacks between divorce, widowhood, and the availability of territories are intricately linked in determining the evolutionary advantage of divorce. We detail testable predictions about populations that should be expected to divorce at high rates.
For many bird species, trade-offs in resource allocation become stark during incubation, when caring demands put into direct conflict their investment in reproduction versus survival. We demonstrate the critical importance of resource allocation, here measured indirectly as body mass, for incubation behavior in the Manx Shearwater (Puffinus puffinus), a biparentally-caring seabird. Using daily measurements of body mass from breeding pairs in combination with field observations and remotely collected behavioral data, we examined how changes in mass related to nest attendance and foraging behavior. We furthermore tested whether this differed between the sexes and between pairs of different breeding experience. We found that while body mass predicted the probability that incubating birds would choose to temporarily desert the nest, incubation shift duration was ultimately set by return of the foraging bird. The trip durations of foraging birds in turn were primarily dictated by their body mass reserves on departure from the nest. However, foragers appeared to account for the condition of the incubating partner by returning from sea earlier when their partner was in poor condition. This key finding suggests that decisions relating to resource allocation may be made cooperatively within the breeding pair during incubation. Our results contribute to understanding the mechanisms by which individuals regulate both their own and their partner’s incubation behavior, with implications for interacting with fine-scale resource availability.
Breeding philopatry is well known in the Black-headed Gull (Chroicocephalus ridibundus). Using a capture-mark-recapture method, we studied if Black-headed Gulls show nest site tenacity and mate fidelity as well, and investigated if there are differences between a stable, and a newly established and fast-growing colony, as well as for differences between the center and edges of these colonies located in north-eastern Germany. We found a high level of nest site tenacity in the center of the stable colony on Böhmke Island, and lower degrees of nest site tenacity at the edge of the same colony and in the newly established and fast-growing colony on Riether Werder. Mate fidelity was very strong in all individuals which returned to their previous breeding place, regardless of the nest site location.
Divorce is widespread among species of birds and may either be an adaptive strategy to secure a better mate or territory or be a nonadaptive result of a failure to maintain the pairbond. I examined the causes and consequences for divorce in the Northern Flicker (Colaptes auratus), a migratory woodpecker with a high annual mortality rate. In a long-term population study of 1,793 breeding pairs over 17 years, the within-season divorce rate was 4.6% and the between-season divorce rate was 15.5%. Retained pairs within a season initiated their renest 5 days faster than divorced birds that had no greater fledgling production, suggesting that within-season divorce was making the best of a bad job with severe time constraints. Poor performance in the year prior to divorce was not strongly associated with divorce, and analysis of multiple breeding stages revealed that divorcing individuals in the subsequent year had later laying dates, smaller clutches, and fewer fledglings than retained pairs but no better performance than widowed individuals. Analyzing the data separately by sex showed that neither males nor females benefitted from divorce. Thus, there is a reproductive cost linked to finding a new partner per se, but no reproductive advantage associated with divorce. New mates after divorce were usually not older (not higher quality) than previous mates, so intrasexual competition was probably not driving partnership splits. The most plausible explanation seems to be a “bet-hedging” hypothesis in which birds re-pair rapidly in spring if their previous mate does not quickly arrive during spring migration. Divorce in Northern Flickers does not appear to be adaptive and future studies on arrival and interactions of individuals in spring will elucidate proximate constraints on relocating the previous partner.
A good overlap between offspring energetic requirements and availability of resources is required for successful reproduction. Accordingly, individuals from numerous species fine-tune their timing of breeding by integrating cues that predict environmental conditions during the offspring period. Besides acquiring information from their direct interaction with the environment (personal information), individuals can integrate information by observing the behaviours or performance of others (social information). The use of social information is often beneficial because the accumulated knowledge of conspecifics may represent a source of information more reliable than the intrinsically more limited personal information. However, although social information constitutes the major source of information in a wide range of contexts, studies investigating its use in the context of timing of breeding are scarce. We investigated whether black-legged kittiwakes (Rissa tridactyla) used social information to adjust the timing of egg-laying. We manipulated social information using a food-supplementation experiment, known to advance kittiwakes' reproductive phenology. We expected food-supplemented and unsupplemented pairs to delay and advance, respectively, their timing of laying when surrounded by a majority of neighbours from the opposite food-treatment. However, both unsupplemented and food-supplemented kittiwakes delayed egg-laying when surrounded by a higher proportion of neighbours from the opposite food-treatment. This result shows that kittiwakes use social information to time egg-laying, but that it is not used to match the seasonal peak of food availability. We suggest that when social and personal cues give contradictory environmental information, individuals may benefit from delaying laying to gather more information to make better decisions about investment into eggs. Further, we explored a potential proximate mechanism for the pattern we report. We show that baseline corticosterone, known to mediate reproductive decisions, was lower in unsupplemented females facing a higher proportion of food-supplemented neighbours. Altogether, our results suggest that to fine-tune their timing of laying, kittiwakes use complex decision-making processes in which social and personal information interplay.
The European Storm-petrel Hydrobates pelagicus is a monogamous and long-lived species with a low reproductive rate. Its nest sites are located in natural cavities under rocks or in burrows excavated by other species. Data obtained in the Molène archipelago, western France, have been analysed to study nest site fidelity and mate fidelity, and to study their relationship with breeding success and sex. Breeders were ringed and breeding success assessed from 2001-18. The influence of age and the weight of breeders on reproductive success has also been studied. Individuals were very faithful to their nest sites (94%) and to their mates (95%) from one year to the next. Breeding failure in the year t was negatively correlated with nest site fidelity and with mate retention in year t+1. Nest site fidelity was not influenced by the sex of breeding birds. Change of nest site or mate had no significant impact on the breeding success in the same year. There was a positive effect of the weight of incubating adults on reproductive success. High rates of nest site fidelity and mate fidelity may indicate good population status, with breeding habitat and mates of good quality.
Divorce occurs when both members of a breeding pair survive to the following year but then pair with other individuals instead of reuniting. Divorce is common in birds, but its frequency can vary widely both between and within species, or even between populations across years. Several explanations for divorce have been described, both adaptive and nonadaptive. Many studies have compared the breeding success of faithful and divorced individuals, but fewer have considered the process of divorce, i.e. the events that lead up to divorce. In this study, we used data from eight breeding seasons to investigate divorce in a population of blue tits, Cyanistes caeruleus, in southern Germany. To compare our results to previous work, we first describe the frequency of divorce and compare the breeding success of divorced and faithful pairs. We then use data from an RFID transponder-based system, where all visits of individuals to any nestbox in the study site are automatically recorded throughout the year, to compare the behaviour of pairs in the interbreeding period. We found that the probability of divorce was not affected by breeding success in Year X. However, divorce was predicted by the difference in arrival time to the study site between the members of Year X pairs. Furthermore, during the interbreeding period, compared to their divorced counterparts, members of faithful pairs had more interactions with one another than with other individuals of the opposite sex. In Year X + 1, faithful females started egg laying earlier, had somewhat larger clutches and produced slightly more fledglings, than females that had divorced. We propose that divorce in blue tits is a by-product of separation of the two pair members after the Year X breeding season, leading to asynchrony in the timing of settlement and pair formation in Year X + 1.
This research describes the breeding ecology, behaviour and substrate preferences of the Australian Fairy Tern, Sternula nereis nereis, in four colonies around Perth, Western Australia between 2018 and 2020. Extensive field observations, supported by a bird banding study and sunrise to sunset video recording were used at colony and roosting sites to determine the processes of mating, colony formation, egg-laying and incubation periods, post-hatching care and breeding success (fledglings per pair). At a colony in North Fremantle, the median nest spacing was 0.71 m (mean ± s.e. = 0.89 ± 0.05 m), which increased over time. Birds establishing nests within a week of the first eggs being laid selected sites with significantly higher percentage beach shell cover (73.5 ± 4.5%) than those laying later in the season (58.2 ± 7.9%) and on average, birds selected sites with higher shell cover (64.9 ± 2.8%, n = 114) than a random sample of sites within the colony (53.7 ± 4.4%, n = 44). Incubation periods ranged from 17 to 26 days (n = 86, mean = 21 ± 0.17 days). Incubation shift duration was highly variable, with both sexes contributing, almost equally to the care of the brood (mean = 1.27 ± 6.11 h). Chicks fledged 21–23 (mean = 22 ± 0.21, n = 10) days following hatching, with all banded juveniles leaving the colony site within 8 days of fledgling. The information gained from this research helps inform conservation strategies for this vulnerable species, where management interventions are frequently necessary to prevent population decline.
Species breeding in urban environments are highly prone to a wide variety of non-natural, human activities, which range from short-term disturbances to the degradation or loss of suitable habitat. The latter in turn may force individuals to relocate to new sites for foraging or breeding, both of which presumably entails fitness costs due the trade-offs of finding and exploring new habitats. Species showing a high level of spatial foraging specialisation or nest site fidelity are expected to be most vulnerable. In this study, we explored the consequences of nest site loss on the reproductive investment of lesser black-backed gulls (Larus fuscus), a site faithful seabird species breeding in an urban environment. We monitored a population of 1.173 colour-ringed gulls across 13 years, that involved several episodes of spatially restricted loss of breeding habitat. We found that birds which lost their breeding territories reduced their investment into the eggs as reflected in a decrease of the clutch volume. They relocated over larger distances compared to birds that relocated voluntarily. Moreover, the likelihood of skipping the subsequent breeding season increased after a forced relocation. These negative effects of forced relocation likely contribute to the decline in the number of breeding pairs in our urban population as observed during the last ten years, and highlights the importance of maintaining a stable breeding environment in urban areas for the conservation of this and potentially other colonial breeding seabird species.
Pair bonds are often maintained through the reciprocal and coordinated exchange of communicative signals. The ability to recognize and appropriately respond to a partner’s signals will define a pair’s ability to reproduce. Individual variation in responsiveness, by shaping the formation and maintenance of strong pair bonds, will ultimately influence an individual’s reproductive output. Throughout the breeding period, female cowbirds (Molothrus ater) respond to male song displays using a vocalization known as the chatter. In this study, we investigated whether variation in chatters remained repeatable across years and predicted reproductive performance. A flock of cowbirds housed in a large aviary complex was observed during the spring of 2011 to 2012. We recorded courtship interactions, including singing behavior for males, and chatters and eggs laid by females. The rate with which females responded to song using chatters remained consistent across years, with some females predictably responding to more songs using chatters than others. During 2012, chattering predicted the number of eggs females laid and her paired status. Paired females were more likely to respond to songs with chatters, and there was a strong positive relationship between the number of eggs laid and the proportion of songs she responded to using chatters. Overall, these findings suggest that variation in female vocal behavior is associated with their reproductive success.
In birds, changing mates generally results in decreased breeding success. Although costs and benefits of pair break-up have been well studied, endocrine mechanisms associated with mate change are poorly known. We measured baseline and stress-induced corticosterone levels in relation to mate change in Black-legged Kittiwakes (Rissa tridactyla). Baseline corticosterone levels were higher in kittiwakes breeding with a new mate than in kittiwakes that did not change mate. Stress-induced corticosterone levels were not influenced by change of mate. Elevated baseline corticosterone levels in birds breeding with a new mate could result from the social stress associated with pair break-up or mirror a higher energetic demand resulting from a lack of coordination between new pair members. Our results emphasize the usefulness of corticosterone levels in elucidating the effects of mate change on the energetic demands of reproduction in free-living birds.
We examined the influence of female age, male age, and pair-bond duration on start of egg-laying, clutch size, and number of young fledged in the Lesser Spotted Woodpecker (Dendrocopos minor). We also attempted to disentangle the relative influence of individual age and pair-bond duration on reproduction, because the effect of those factors may be confounded. Breeding performance improved with age in that old females started egg-laying earlier and old males raised more young than yearlings, and old pairs both started egg-laying earlier and raised more young than new pairs. Clutch size was not affected by age, but showed a strong negative relation with laying date. Late-laying yearling females experienced a lower survival, and the survival of yearling males showed a positive relation with fledgling production. That differential survival was a likely mechanism explaining the differences in reproductive performance between yearling and old birds. Several analyses suggested that pair-bond duration had independent positive effects on reproduction. Benefit of long-term pair-bonds appeared to depend upon repeated breeding with a particular partner. The mechanisms behind the benefit of remating with a particular partner remain unclear, however. We postulate that much of the patterns of age effects on reproduction in the Lesser Spotted Woodpecker may be caused by constraints posed by the territorial system and effects of territory quality, although effects of individual quality can not be excluded.
Several factors shape lifetime reproductive success, including genetic background, body condition, environmental conditions and ecological interactions such as parasitism. Adults often show higher reproductive success than their young conspecifics, especially in long‐lived bird species, and this may be explained by the cumulative effects of an increase in reproductive experience and the selection of high‐quality individuals from one year to another. To test whether this pattern also exists in short‐lived bird species, we used 13 years of monitoring data from two Great Tit Parus major populations. The effects of male and female age on several reproductive parameters were analysed in 419 pairs of Great Tits, whilst accounting for body condition and infection by haemosporidian parasites. Reproductive success was mainly affected by the age‐class of males. Pairs containing a sub‐adult male fledged one‐third fewer chicks than pairs containing an adult male. The difference was not caused by variation in male fertility but could have been caused by better parental care provided by adult birds. In addition to lower reproductive success, first‐year males also had reduced access to mating compared to adult males, suggesting an avoidance of sub‐adult males by females. Nestling body condition was positively correlated with parental body condition, and the body condition of male and female members of breeding pairs was positively correlated. Finally, the number of fledged chicks was mainly affected by the infection status of males. This results temper our previously published results showing an effect of infection on Great Tit reproduction regardless of their sex. In this previous study, and as in most cases, the status of the partner was not taken into account and we show here that this is essential because it can lead to a biased interpretation of the results. This article is protected by copyright. All rights reserved.
Social monogamy has evolved multiple times and is particularly common in birds. However, it is not well understood why some species live in long-lasting monogamous partnerships while others change mates between breeding attempts. Here, we investigate mate fidelity in a sequential polygamous shorebird, the snowy plover (Charadrius nivosus), a species in which both males and females may have several breeding attempts within a breeding season with the same or different mates. Using six years of data from a well-monitored population in Bahía de Ceuta, Mexico, we investigated predictors and fitness implications of mate fidelity both within and between years. We show that in order to maximize reproductive success within a season, individuals divorce after successful nesting and re-mate with the same partner after nest failure. Therefore, divorced plovers, counterintuitively, achieve higher reproductive success than individuals that retain their mate. We also show that different mating decisions between sexes predict different breeding dispersal patterns. Taken together, our findings imply that divorce is an adaptive strategy to improve reproductive success in a stochastic environment. Understanding mate fidelity is important for the evolution of monogamy and polygamy, and these mating behaviours have implications for reproductive success and population productivity.
In species with biparental care, individuals only have to pay the costs for their own parental investment, whereas the contribution of their partner comes for free. Each parent hence benefits if its partner works harder, creating an evolutionary conflict of interest. How parents resolve this conflict and how they achieve the optimal division of parental tasks often remains elusive. In this study, we investigated whether lesser black-backed gulls (Larus fuscus) divide parental care during incubation equally and whether this correlates with the extent of vocalizations between pair-members during incubation. We then investigated whether pairs showing more evenly distributed incubation behavior had a higher reproductive success. To this end, we recorded incubation behavior and vocalizations for 24-h time periods. Subsequently, we experimentally increased or decreased brood sizes in order to manipulate parental effort, and followed offspring development from hatching till fledging. Although incubation bouts were, on average, slightly longer in females, patterns varied strongly between pairs, ranging from primarily female incubation over equal sex contributions to male-biased incubation. Pairs contributing more equally to incubation vocalized more during nest relief and had a higher reproductive output when brood sizes were experimentally increased. Thus, vocalizations and a more equal division of parental care during incubation may facilitate higher levels of care during the nestling period, as suggested by a greater reproductive success when facing high brood demand, or they indicate pair quality.
Trade‐offs between current and future reproduction are central to the evolution of life histories. Experiments that manipulate brood size provide an effective approach to investigating future costs of current reproduction. Most manipulative studies to date, however, have addressed only the short‐term effects of brood size manipulation. Our goal was to determine whether survival or breeding costs of reproduction in a long‐lived species manifest beyond the subsequent breeding season. To this end, we investigated long‐term survival and breeding effects of a multi‐year reproductive cost experiment conducted on Black‐legged Kittiwakes (Rissa tridactyla), a long‐lived colonial nesting seabird. We used multi‐state capture‐recapture modeling to assess hypotheses regarding the role of experimentally reduced breeding effort and other factors, including climate phase and colony size and productivity, on future survival and breeding probabilities during the 16‐year period following the experiment. We found that forced nest failures had a positive effect on breeding probability over time, but had no effect on long‐term survival. This apparent canalization of survival suggests that adult survival is the most important parameter influencing fitness in this long‐lived species, and that adults should pay reproductive costs in ways that do not compromise this critical life history parameter. When declines in adult survival rate are observed, they may indicate populations of conservation concern.
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Interannual mate and site fidelity is common in migratory shorebirds with monogamous mating systems. After long-distance migrations and separation during the winter, birds often relocate their former mate at their previous breeding territory. Although pairs frequently reunite, new pairs are also formed. Why birds change mates is still not completely understood. Mate change can involve active decisions, in which one or both mates actively chooses to divorce from a previous mate, but can also be related to arrival timing or mate availability at the breeding grounds. We explored possible causes of mate change in the Pacific subspecies of the migratory shorebird Dunlin (Calidris alpina pacifica) breeding at the subarctic Yukon-Kuskokwim Delta, Alaska, USA (61°36′N, 165°12′W). Interannual return rates of Dunlin to their breeding grounds were higher for males (74%) than for females (54%) and were 14% higher for birds with high previous breeding success. Mate change was rare if both birds returned to the breeding grounds in a consecutive breeding season: only 8% of all pairs divorced when previous mates were available. When former mates failed to return or returned late, however, many individuals formed new pairs (45% of males and 53% of females). Nest initiation dates were not delayed for new pairs compared to reuniting pairs, and nest survival did not differ between new and reuniting pairs; however, renesting after nest failure within a season was faster for reuniting pairs. We conclude that avoiding delayed nesting is a strong determinant of breeding decisions in Pacific Dunlin nesting in the short subarctic summer.
Bottleneck episodes may occur in small and isolated animal populations, which may result in decreased genetic diversity and increased inbreeding, but also in mating strategy adjustment. This was evaluated in the vulnerable and socially monogamous Monteiro’s Storm-petrel Hydrobates monteiroi, a seabird endemic to the Azores archipelago which has suffered a dramatic population decline since the XVth century. To do this, we conducted a genetic study (18 microsatellite markers) in the population from Praia islet, which has been monitored over 16 years. We found no evidence that a genetic bottleneck was associated with this demographic decline. Monteiro’s Storm-petrels paired randomly with respect to genetic relatedness and body measurements. Pair fecundity was unrelated to genetic relatedness between partners. We detected only two cases of extra-pair parentage associated with an extra-pair copulation (out of 71 offspring). Unsuccessful pairs were most likely to divorce the next year, but genetic relatedness between pair mates and pair breeding experience did not influence divorce. Divorce enabled individuals to improve their reproductive performances after re-mating only when the new partner was experienced. Re-pairing with an experienced partner occurred more frequently when divorcees changed nest than when they retained their nest. This study shows that even in strongly reduced populations, genetic diversity can be maintained, inbreeding does not necessarily occur, and random pairing is not risky in terms of pair lifetime reproductive success. Given, however, that we found no clear phenotypic mate choice criteria, the part played by non-morphological traits should be assessed more accurately in order to better understand seabird mating strategies.
In social species individuals living in the same group may synchronize activities such as movements, foraging or antipredator vigilance. Synchronization of activities can also be observed between partners especially during breeding and can be crucial for breeding success. Vocalizations are behaviours that can be coordinated between individuals, but simultaneous vocalizations in groups have mostly been considered as noise that does not bear any information. Indeed, little is known about the structure and function of vocal communications involving a network of individuals. How individual vocal activity forms part of the communal sound and how the group influences individual vocal activity are questions that remain to be studied. Zebra finches, Taeniopygia guttata, are social, monogamous songbirds that form lifelong pair bonds. In the wild, they are typically found in small groups, with the pair as the primary social unit, and they gather in ‘social’ trees where both females and males produce vocalizations. Here we investigated in the laboratory the influence of group size and composition on general vocal activity and synchrony, as well as the influence of pair bond and spatial location on the finer characteristics of dyads' vocal interactions. We used a set-up that locked the birds at fixed spatial positions of our choosing to control the proximity network and allowed us to match most of the vocalizations with specific individuals. We used an in-house software suite that automatically detects vocalizations from hours of passive recording. We found that zebra finch groups synchronized their general vocal activity with waves of collective vocalizations, which depended on both the size and the composition of the group. The acoustic network was shaped by pair bonds at different timescales. Birds preferentially vocalized close in time to (synchrony) or directly after (turn taking) their partner when it was present and the nearest neighbour when the partner was not available.
The quality of conditions provided by avian parents will have consequences for both parental and offspring fitness. While many components of avian reproduction appear to vary with parental age, the effect of age on incubation has largely been ignored so far. In this study, we tested whether young herring gulls provide a different incubation environment from mature ones and whether this has consequences for offspring performance. Laying and rearing conditions were standardised using a cross-fostering protocol. Egg predation rates tended to be higher in the nests of young parents. However, nest site, nest construction and egg temperature during incubation did not vary with parental age. Overall, the duration of incubation was shorter in young compared to mature birds and this reflected the later laying date of the former, since incubation duration generally decreased across the season. However, male eggs incubated by young parents had longer incubation periods than predicted for their laying dates. In contrast, incubation length of female eggs incubated by young pairs, and of male and female eggs incubated by mature birds did not deviate from the expected for any given laying date. Offspring that had been incubated by young parents had considerably poorer survival than those incubated by mature pairs, despite being reared under standardized, favourable conditions (singly, by mature parents). This was due to increased mortality among female chicks that had been incubated by young parents. The chicks incubated as eggs by young and mature birds, which survived until fledging, did not differ in body mass and size growth, or body condition. The results of this study demonstrate that parental age can influence offspring performance via variation in incubation environment, and that females are more susceptible than males to conditions experienced during embryonic development.
Breeding dispersal is the movement of an individual between breeding attempts and is usually associated with the disruption of the social pair bond, although mates may disperse together as a social unit. In monogamous territorial species, the decision to disperse may be affected by individual attributes such as sex, age and condition of the disperser. However, environmental and social contexts may also play a crucial role in the decision to disperse. We analysed capture-resighting data collected over 9 years to study breeding dispersal and divorce rates of a Southern House Wren Troglodytes aedon musculus population in South Temperate Argentina. Between-season dispersal was more frequent than within-season dispersal, with females dispersing more often than males, both between and within seasons. Both within-season and between-season breeding dispersal probability was affected by territory availability, but not by previous breeding success. When the adult sex ratio (ASR) was more skewed towards males, male between-season dispersal was also affected by mating status, with widowed and single males dispersing more often than paired males. Within-season divorce increased the reproductive success of females but not males, and was affected by the availability of social partners (with increasingly male-skewed ASR). Our results suggest that territorial vacancies and mating opportunities affect dispersal and divorce rates in resident Southern House Wrens, highlighting the importance of social and environmental contexts for dispersal behaviour and the stability of social pair bonds.
Individuals in species with long-term social monogamy often incur fitness costs after mate change. We evaluated the relative contributions of mate familiarity and male breeding experience to the costs of mate change of female black brant geese (Branta bernicla nigricans). We assessed the effects of mate change on relative nest initiation date, clutch size, brood size at hatch, growth rates of goslings, and prefledging survival of offspring. We modeled variation in relative nest initiation dates, clutch size, initial brood size, and gosling growth rates using generalized linear mixed models in Program R. We estimated prefledging survival with Cormack–Jolly–Seber models in Program MARK using reencounters of webtagged goslings. Mate change had a small effect on relative nest initiation date, clutch size, and initial brood size, but no effect on growth rates of brant goslings. Females breeding with an unfamiliar, but experienced male had goslings with higher prefledging survival rates (ϕ = 0.44±0.11 [95% confidence interval]) than those breeding with a familiar, experienced mate (ϕ = 0.30±0.04). However, females that changed mates and re-paired with an inexperienced male had goslings with substantially lower prefledging survival rates (ϕ = 0.20±0.04) than any other group of females. Our findings indicate that reproductive output by female brant is affected by male experience rather than mate familiarity. We believe that female brant typically benefit from mate retention because most will not acquire an experienced partner after mate change.
This study was attended in Tehsil Mansehra of District Mansehra during the breeding period
April-July 2012. The mean clutch size documented was 3.3 with eggs range 2-4. Mean egg
length and breadth was 24.5±2.6mm and 20.3±1.7mm, mean egg volume was 5.24±1.2cm3 and
egg shape index calculated to be 1.20±0.02. Mean weight of the egg recorded was 4.5±1.09g.
There is no substantial corelation exists between egg length and breadth (P>0.05) and likewise
between weight and volume of Black Drongo eggs there was no meaningfully statistical
difference exists (P>0.05). Hatchling success was 71.1% and fledgling success was 64.7%.
Capsule: Young birds are less likely to have high reproductive success compared with older ones because of a lack of several skills influencing breeding performance. Aims: To test the 'constraint' hypothesis by investigating the effect of male and female age on reproductive performance of a Bluethroat Luscinia svecica population. Methods: We compared two age-classes (yearling versus old), breeding for the first time at Guérande salt-pans, France, by evaluating arrival dates on breeding site, territory quality, laying dates, clutch size and egg size, delay before re-nesting, breeding performance, feeding rate at two different nestling periods (on days 4-5 and 10-11 after hatching) and nestling body condition. Results: Our results clearly demonstrated an age effect on reproductive performance for both males and females: young breeders were less likely to fledge young. In older males, improvement of reproductive success was related to feeding rate during the first nestling period. For females, timing of breeding (laying date) and reproductive investment (such as clutch size, feeding rate in the whole nestling period, brood condition) were the main determinants. The presence of a yearling in a pair strongly decreased the number of young produced per breeding season. Conclusion: Bluethroat supported the 'constraint' hypothesis, i.e. that behavioural and physiological maturation is needed for young breeders to enhance reproductive performance.
Clutch size of the kittiwake is influenced by the previous breeding experience of the female and also by the time of laying. Both of these factors play a part in determining the clutch size and the correlation between breeding experience and clutch size is not solely the result of older birds breeding earlier. The clutches laid by females breeding for the first time are, on average, smaller than those laid at the same time by more experienced breeders and are less influenced by the time of breeding. No female breeding for the first time has been found to lay three eggs. There is a correlation between the time of the onset of breeding in kittiwake colonies and the average clutch size. It is suggested that a progressive decrease in the clutch size as the breeding season progresses may be widespread in both passerines and non-passerines and probably occurs only in species which do not normally have two broods in a single breeding season.
In 1938, Fraser Darling put forward the concept of “social stimulation” This hypothesis postulated that colonial-nesting birds received stimulation from their neighbours which resulted in earlier breeding, a shorter spread of the nesting period in the colony and greater breeding success.
Darling's hypothesis has been criticized from a number of points of view. His original data were not sufficient to show significant differences between the behaviour of large and small colonies of the Herring Gull Larus argentatus and of the Lesser Blackbacked Gull L. fuscus. Furthermore, the present authors have shown that large colonies of the Kittiwake Rissa tridactyla have a longer nesting period than small colonies. While these and other facts cast doubt on the importance of the “Fraser Darling effect” they do not disprove the possibility that neighbouring birds in a colony may stimulate each other. Studies have therefore been undertaken on colonies of the Kittiwake on the Durham, Northumberland and East Lothian coasts to test as thoroughly as possible whether or not social stimulation is of importance to colonial-nesting birds.
The colonies studied in greatest detail were close together and it is possible to exclude the possible effects of the physical environment affecting the colonies in a different manner. Differences of up to 21 days were observed between the mean time of breeding of nine colonies, and since the differences were greatest in the youngest colonies, the effect of differences in the age composition of the colonies was considered. A study of colourringed Kittiwakes showed that females which were breeding for at least the fourth time bred 9.8 days earlier than females which were breeding for the first time. When, however, the age composition of the colonies was determined, it was always found that less than 20% of the observed differences in the time of breeding could be accounted for by differences in the age composition.
A study of the nest densities within individual colonies showed that the time of breeding was related to the density of nests. Thus, at an average density of nine nests within a radius of 5 ft. of each nest, the time of breeding was about 18 days earlier than on sites where the equivalent density was about two nests.
It was observed that the colonies with the highest density also had the greatest range of nest densities. The colonies differed from each other in the mean density and also the maximum density attained, but were similar in that they all had some nests which had no other nests within a 5 ft. radius. Since breeding is earlier at higher densities, these observations can explain the earlier onset of breeding and greater spread of breeding in the denser colonies and also that the last birds to breed in each colony do so at the same time.
Observations show that the time of return to the colonies is also related to nest-density and, together with other evidence, suggest that the effect on the birds of the density of their breeding neighhours is carried over from one year to the next.
It follows from these studies that social stimulation has a distinct effect on the breeding condition of birds within Kittiwake colonies.
1. From 1954 to 1956 inclusive, the biology of individual marked Kittiwakes was studied at North Shields, Northumberland.
2. It was concluded that older Kittiwakes reacted to the breeding stimulus earlier, more intensively and with greater success than younger breeding birds.
3. Birds with previous breeding experience returned to the colony before birds breeding for the first time and these before non-breeders.
4. Before breeding started, birds which had bred previously spent more of their time at the colony than those about to breed for the first time.
5. Birds breeding for at least the second time laid the first egg 7·5 days earlier than those breeding for the first time.
6. Breeding started one day later for every four days the return to the colony was postponed.
7. Older breeding birds showed greater nest-site tenacity, laid larger clutches and had greater breeding success than younger birds.
8. The chicks in broods of two (but not of one) increased in weight more rapidly where the parents had previous experience.
9. Breeding Kittiwakes showed strong colony tenacity, but 24% of the marked non-breeding birds were subsequently seen in other colonies.
10. Over half the birds retained the same mate as in the previous year.
A Population Study of Penguins. Oxford. This content downloaded from 130.132.123.28 on Fri
- L E Richdale
Richdale, L. E, (1957). A Population Study of Penguins. Oxford. This content downloaded from 130.132.123.28 on Fri, 2 May 2014 21:21:03 PM All use subject to JSTOR Terms and Conditions