[Show abstract][Hide abstract] ABSTRACT: Absent repeat calls (ARC) are produced by nestlings of some bird species when parents are not at the nest, and play a role in sibling interactions and parental investment. We explored if individual traits influencing begging also determine ARC in the spotless starling (Sturnus unicolor), and whether this behaviour explains nestling feeding success. We video-taped natural broods and examined the effects of experimental feeding in this behaviour. Experimentally fed chicks stopped calling and received fewer feedings. Among un-fed chicks, absence calls were more frequent in smaller nestlings. We found a positive relationship between nestling reaction time to parental arrival and food acquisition: chicks that reacted first received more feedings that slower chicks. ARC performance was also positively related to reaction time: chicks that produced more calls also reacted first to parents. These results suggest that ARC may have important effects on resource allocation and family interaction networks.
[Show abstract][Hide abstract] ABSTRACT: Female birds may adjust their offspring phenotype to the specific requirements of the environment by differential allocation of physiologically active substances into yolks, such as androgens. Yolk androgens have been shown to boost embryonic development, growth rate and competitive ability of nestlings, but they can also entail immunological costs. The balance between costs and benefits of androgen allocation is expected to depend on nestling environment. We tested this hypothesis in a multi-brooded passerine, the spotless starling, Sturnus unicolor. We experimentally manipulated yolk androgen levels using a between-brood design, and evaluated its effects on nestling development, survival and immune function. Both in first and replacement broods, the embryonic development period was shorter for androgen-treated chicks than controls, but there were no differences in second broods. In replacement broods, androgen-treated chicks were heavier and larger than those hatched from control eggs, but this effect was not observed in the other breeding attempts. Androgen exposure reduced survival with respect to controls only in second broods. Regarding immune function, we detected non-significant trends for androgen treatment to activate two important components of innate and adaptive immunity (IL-6 and Ig-A levels, respectively). Similarly, androgen-treated chicks showed greater lymphocyte proliferation than controls in the first brood and an opposite trend in the second brood. Our results indicate that yolk androgen effects on nestling development and immunity depend on the environmental conditions of each breeding attempt. Variation in maternal androgen allocation to eggs could be explained as the result of context-dependent optimal strategies to maximize offspring fitness. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Full-text · Article · Jun 2015 · Journal of Evolutionary Biology
[Show abstract][Hide abstract] ABSTRACT: Lipid peroxidation products are widely used as markers of oxidative damage in the organism. To properly interpret the information provided by these markers, it is necessary to know potential sources of bias and control confounding factors. Here, we investigated the relationship between two indicators of lipid mobilization (circulating levels of triglycerides and cholesterol) and two common markers of oxidative damage (plasma levels of malondialdehyde and hydroperoxides; the latter estimated from the d-ROMs assay kit). The following five avian species were studied: red-legged partridge (Alectoris rufa), zebra finch (Taeniopygia guttata), spotless starling (Sturnus unicolor), marsh harrier (Circus aeroginosus), and Montagu’s harrier (Circus pygargus). In all cases, plasma triglyceride levels positively and significantly correlated with lipid peroxidation markers, explaining between 8% and 34% of their variability. Plasma cholesterol, in contrast, showed a significant positive relationship only among spotless starling nestlings and a marginally significant association in zebra finches. These results indicate that lipid peroxidation marker levels covary with circulating lipid levels. We discuss the potential causes and implications of this covariation and recommend that future studies that measure oxidative damage using lipid peroxidation markers report both raw and relative levels (i.e., corrected for circulating triglycerides). Whether the observed pattern also holds for other tissues and in other taxa would deserve further research.
Full-text · Article · Feb 2015 · Physiological and Biochemical Zoology
[Show abstract][Hide abstract] ABSTRACT: Eye size shows a large degree of variation among species, even after correcting for body size. In birds, relatively larger eyes have been linked to predation risk, capture of mobile prey, and nocturnal habits. Relatively larger eyes enhance visual acuity and also allow birds to forage and communicate in low-light situations. Complex habitats such as tropical rain forests provide a mosaic of diverse lighting conditions, including differences among forest strata and at different distances from the forest edge. We examined in an Amazonian forest bird community whether microhabitat occupancy (defined by edge avoidance and forest stratum) was a predictor of relative eye size. We found that relative eye size increased with edge avoidance, but did not differ according to forest stratum. Nevertheless, the relationship between edge avoidance and relative eye size showed a nonsignificant positive trend for species that inhabit lower forest strata. Our analysis shows that birds that avoid forest edges have larger eyes than those living in lighter parts. We expect that this adaptation may allow birds to increase their active daily period in dim areas of the forest. The pattern that we found raises the question of what factors may limit the evolution of large eyes.
Full-text · Article · Oct 2014 · Ecology and Evolution
[Show abstract][Hide abstract] ABSTRACT: Anthropogenic noise is a major pollutant for organisms that live in urban areas. City birds modify their songs in ways that can increase their communication potential in spite of noise. However, these changes cannot prevent song masking by the extremely loud noises to which some urban bird populations are exposed. Here, we show that birds near a major airport advance their dawn singing time, thus reducing overlap with periods of intense aircraft noise. This modification was stronger in species whose normal singing time was relatively late, those which overlapped the most with aircraft noise. Although suggestive of a causal relationship, this pattern does not allow us to tell apart the effect of aircraft noise from that of other variables that may correlate with dawn singing time. In order to control for such potentially confounding variables, we replicated the study in several airports at different latitudes in Spain and Germany. The results show that indeed the overlap of song chorus with aircraft noise was the key factor that influenced time advancement. Aircraft traffic time was the main predictor of song advancement: across Europe, those bird populations whose singing time overlapped the most with aircraft traffic were those that advanced their song timing to a higher extent. Our results exemplify how behavioral plasticity may allow the survival of avian populations in areas of high noise pollution. However, such an adaptation likely involves departing from optimal singing times, leading to higher energetic costs and amplifying between-species differences in competitive ability and resilience.
No preview · Article · Mar 2014 · Behavioral Ecology
[Show abstract][Hide abstract] ABSTRACT: Several techniques in ecological immunology have been used to assess bird immunocompetence thus providing useful information to understand the contribution of the immunological system in life-history decisions. The phytohaemagglutinin (PHA)-skin test has been the most widely employed technique being interpreted as the sole result of T lymphocytes proliferation and hence used to evaluate acquired immunological capacity. However, the presence of high numbers of phagocytic cells in the swelling point has cast some doubt about such an assumption. To address this issue, we collected blood from 14 days-old nestlings of spotless starling (Sturnus unicolor), administered subcutaneous PHA immediately after and then measured the swelling response 24 hours later. Differential counts of white blood cells suggested that an intense development of acquired immunological defences was taking place. The phagocytic activity of both heterophiles and monocytes was also very intense as it was the swelling response. Moreover, our results show, for the first time in birds, a positive relationship between the phagocytic activity of both kinds of cells and the swelling response. This broadens the significance of the PHA test from reflecting T lymphocytes proliferation -as previously proposed but still undetermined in vivo- to evaluate phagocytosis as well. In other words, our data suggest that the PHA swelling response may not be considered as the only consequence of processes of specific and induced immunity -T lymphocytes proliferation- but also of constitutive and nonspecific immunity -heterophiles and monocytes phagocytosis. We propose the extensive use of PHA-skin test as an optimal technique to assess immunocompetence.
[Show abstract][Hide abstract] ABSTRACT: Begging in birds is a complex behaviour used by nestlings to solicit feeds from caregivers. Besides calling when parents are present, nestlings of some species also perform less conspicuous repeat calls when parents are absent. The fact that these calls are produced when parents are not at the nest does not mean that parents cannot hear them when they approach the nest or forage in its vicinity. In this study, we experimentally investigated the relationship between parent-absent repeat calls (ARC) and frequency of parental visits, considering parent/offspring communication as a possible implication of these acoustic signals. A playback experiment was conducted to detect changes in parental investment in response to increases in parent-ARC, expecting a differential sexual response. Results showed that females clearly responded to repeat calls, increasing their visit rate significantly with respect to females that received the control treatment. Males, on the contrary, did not change their visit rate in response to the treatment. This result provides evidence for a role of parent/offspring communication in parent-absent repeat calling, an additional function to sibling negotiation processes. The sex-specific response that we found is in agreement with previous studies that have found that females are more responsive than males to variation in solicitation and hunger signals performed by nestlings.
[Show abstract][Hide abstract] ABSTRACT: Variable environments impose constraints on adaptation by modifying selection gradients unpredictably. Optimal bird development requires an adequate thermal range, outside which temperatures can alter nestling physiology, condition and survival. We studied the effect of temperature and nest heat exposure on the reproductive success of a population of double-brooded Spotless Starlings Sturnus unicolor breeding in a nestbox colony in central Spain with a marked intra-seasonal variation in temperature. We assessed whether the effect of temperature differed between first and second broods, thus constraining optimal nest-site choice. Ambient temperature changed greatly during the chick-rearing period and had a strong influence on nestling mass and all body size measures we recorded, although patterns of clutch size or nestling mortality were not influenced. This effect differed between first and second broods: nestlings were found to have longer wings and bills with increasing temperature in first broods, whereas the effect was the opposite in second broods. Ambient temperature was not related to nestling body mass or tarsus-length in first broods, but in second broods, nestlings were lighter and had smaller tarsi with higher ambient temperatures. The exposure of nestboxes to heat influenced nestling morphology: heat exposure index was negatively related to nestling body mass and wing-length in second broods, but not in first broods. Furthermore, there was a positive relationship between nest heat exposure and nestling dehydration. Our results suggest that optimal nest choice is constrained by varying environmental conditions in birds breeding over prolonged periods, and that there should be selection for parents to switch from sun-exposed to sun-protected nest-sites as the season progresses. However, nest-site availability and competition for sites are likely to impose constraints on this choice.
[Show abstract][Hide abstract] ABSTRACT: Yolk androgens in avian eggs play a significant role in embryo and nestling development. However, few studies have examined the differential effect of two of the main yolk androgens, testosterone (T) and androstenedione (A4). Here, we injected eggs of spotless starlings with physiological levels of either T, A4, the combination T+A4 or vehicle substance (control), to examine the differential ability of these steroids to influence nestling development. We found that the duration of the embryonic period was increased by T, and less so by A4, but not by the combination T+A4. Body condition was reduced in all experimental treatments where A4 was present, particularly so in the combination T+A4. Tarsus length was increased in males by A4, and in a lower degree by T, whereas the combination T+A4 inhibited growth. However, these differences in tarsus length between groups disappeared at the end of the nestling period. Cell-mediated immune responsiveness was marginally affected by the interaction between treatment and sex. These patterns suggest that in this species, T has a stronger influence during embryo development than A4, whereas during nestling development the capacities of both androgens to influence growth are similar. The combination T+A4 showed non-additive effects, suggesting either some kind of inhibition between the two androgens, or else an excessive effect due to a bell-shaped pattern of response. Our results suggest a complex picture of sex and age-dependent effects of T and A4, and underline the necessity of further research in the metabolism and action of egg androgens.
Full-text · Article · Sep 2013 · General and Comparative Endocrinology
[Show abstract][Hide abstract] ABSTRACT: In noisy conditions, several avian species modulate their songs in amplitude and in the temporal or frequency domains, presumably to improve communication. Most studies on how passerine birds perform such adjustments have been carried out in oscines, a group well known for the importance of learning in the development of their songs. On the other hand, suboscines, in which learning appears to have little influence on the development of their songs, have been largely neglected. We evaluated song adjustment to noise in the vermilion flycatcher (Pyrocephalus rubinus), a suboscine bird. We conducted song recordings and noise measurements at several territories within Mexico City during the length of the dawn chorus. Males living in noisier places sang long songs, while those males inhabiting quieter places sang both short and long songs. We also found evidence of individual song plasticity, as males sang less versatile songs (i.e., songs with more introductory elements) later in the morning when noise levels were higher. This individual shift in song seems to be more associated to time of the day rather than to the observed rise in noise. However, we cannot discard an effect of noise, which should be evaluated with an experiment. We discuss our results in the context of other studies with oscine passerines and other taxa and consider implications for signaling in intra- and intersexual contexts.
Full-text · Article · Jan 2013 · Behavioral Ecology and Sociobiology
[Show abstract][Hide abstract] ABSTRACT: Song learning has evolved within several avian groups. Although its evolutionary advantage is not clear, it has been proposed that song learning may be advantageous in allowing birds to adapt their songs to the local acoustic environment. To test this hypothesis, we analysed patterns of song adjustment to noisy environments and explored their possible link to song learning. Bird vocalizations can be masked by low-frequency noise, and birds respond to this by singing higher-pitched songs. Most reports of this strategy involve oscines, a group of birds with learning-based song variability, and it is doubtful whether species that lack song learning (e.g. suboscines) can adjust their songs to noisy environments. We address this question by comparing the degree of song adjustment to noise in a large sample of oscines (17 populations, 14 species) and suboscines (11 populations, 7 species), recorded in Brazil (Manaus, Brasilia and Curitiba) and Mexico City. We found a significantly stronger association between minimum song frequency and noise levels (effect size) in oscines than in suboscines, suggesting a tighter match in oscines between song transmission capacity and ambient acoustics. Suboscines may be more vulnerable to acoustic pollution than oscines and thus less capable of colonizing cities or acoustically novel habitats. Additionally, we found that species whose song frequency was more divergent between populations showed tighter noise-song frequency associations. Our results suggest that song learning and/or song plasticity allows adaptation to new habitats and that this selective advantage may be linked to the evolution of song learning and plasticity.
No preview · Article · Aug 2012 · Journal of Evolutionary Biology
[Show abstract][Hide abstract] ABSTRACT: Recent changes in migration distances and propensity for migration associated with climate change have suggested that these traits can evolve rapidly. Part of this rapid response to selection may be due to maternal effects that facilitate changes in the underlying physiology of migration. We hypothesize that exposure to large amounts of antioxidants in the egg will facilitate assimilation and metabolism of dietary antioxidants later in life, thereby allowing offspring to better cope with extreme strenuous exercise such as the bursts of rapid migration shown during spring migration. We tested the relationship between temporal change in mean arrival date of migratory birds since 1960 and concentrations of 2 antioxidants in the eggs of 14 species of birds. Only egg concentration of vitamin E was a significant predictor of advancement in spring arrival date. Furthermore, we experimentally manipulated egg content of vitamin E in barn swallows Hirundo rustica and subsequently recorded arrival date of yearling male recruits. Arrival date advanced significantly by > 1 standard deviation due to treatment, providing experimental evidence for a relationship between egg concentration of vitamin E and subsequent migration behavior. These results are consistent with the hypothesis that maternal effects have played an important role in the evolution of bird migration.
[Show abstract][Hide abstract] ABSTRACT: 1. The immunocompetence handicap hypothesis (ICHH) proposes that androgen-induced immunosuppression is the mechanism that restricts the expression of exaggerated male ornaments to superior males. Numerous tests of this hypothesis have been conducted on the humoral and cell-mediated components of immunity, with mixed results. Surprisingly, no study so far has addressed whether macrophage phagocytosis, a basic immune function, plays a role in the ICHH.
2. We tested whether the ornament size of male spotless starlings (Sturnus unicolor) is a predictor of in vitro macrophage phagocytosis. We found that a moderate physiological concentration of testosterone (T) induced strong phagocytic inhibition. We found no relationship between ornament size and phagocytic activity in basal conditions.
3. Basal phagocytosis was not significantly predicted by ornament size or original testosterone levels. Contrary to expectations, phagocytosis under a moderate T concentration was negatively related to ornament size. Furthermore, a nonsignificant trend for original T concentration to negatively affect T-medium phagocytosis was also found.
4. Our results provide support to the ICCH and suggest that males with exaggerated ornaments and high T concentrations may counteract the inhibitory action of testosterone by some compensatory mechanism. Possible candidates include the presence of immunoenhancing substances, such as melatonin or antioxidants, or differential receptor activity. These mechanisms should be evaluated when testing the reliability of the ICCH in wild populations.
[Show abstract][Hide abstract] ABSTRACT: Research has shown that bird songs are modified in different ways to deal with urban noise and promote signal transmission through noisy environments. Urban noise is composed of low frequencies, thus the observation that songs have a higher minimum frequency in noisy places suggests this is a way of avoiding noise masking. Most studies are correlative and there is as yet little experimental evidence that this is a short-term mechanism owing to individual plasticity. Here we experimentally test if house finches (Carpodacus mexicanus) can modulate the minimum frequency of their songs in response to different noise levels. We exposed singing males to three continuous treatments: low-high-low noise levels. We found a significant increase in minimum frequency from low to high and a decrement from high to low treatments. We also found that this was mostly achieved by modifying the frequency of the same low-frequency syllable types used in the different treatments. When different low-frequency syllables were used, those sung during the noisy condition were longer than the ones sang during the quiet condition. We conclude that house finches modify their songs in several ways in response to urban noise, thus providing evidence of a short-term acoustic adaptation.
[Show abstract][Hide abstract] ABSTRACT: Recent changes in migration distances and propensity for migration associated with climate change have suggested that these traits can evolve rapidly. Part of this rapid response to selection may be due to maternal effects that facilitate changes in the underlying physiology of migration. We hypothesize that exposure to large amounts of antioxidants in the egg will facilitate assimilation and metabolism of dietary antioxidants later in life, thereby allowing offspring to better cope with extreme strenuous exercise such as the bursts of rapid migration shown during spring migration. We tested the relationship between temporal change in mean arrival date of migratory birds since 1960 and concentrations of 2 antioxidants in the eggs of 14 species of birds. Only egg concentration of vitamin E was a significant predictor of advancement in spring arrival date. Furthermore, we experimentally manipulated egg content of vitamin E in barn swallows Hirundo rustica and subsequently recorded arrival date of yearling male recruits. Arrival date advanced significantly by >1 standard deviation due to treatment, providing experimental evidence for a relationship between egg concentration of vitamin E and subsequent migration behavior. These results are consistent with the hypothesis that maternal effects have played an important role in the evolution of bird migration.
[Show abstract][Hide abstract] ABSTRACT: 1. Social and ecological conditions experienced by individuals during early life can strongly influence their development and survival. Nestlings of many species present important variations in plasma androgens that can be associated with begging and sibling competition and may translate into fitness effects, since broods with higher testosterone (T) production may have better body condition and higher fledging success. However, the positive effects of androgens may be counterbalanced by a reduction of immune defences and a greater susceptibility to diseases.
2. In this study we examined the potential relationships between natural variation in plasma T, immunity and post-fledging survival rate in nestlings of the spotless starling (Sturnus unicolor).
3. We found that nestlings with higher cellular-mediated immune responses (CMI; measured as a swelling response to phytohaemagglutinin injection) were more likely to be recruited in the population than nestlings with lower CMI responses. Males presented higher CMI response than females, possibly due to differences in competitive advantage over food. We also found that CMI response was negatively related to T levels, as predicted by the immunocompetence handicap hypothesis. However, despite this reduction in CMI response, we failed to find an association between nestling T levels and survival prospects. Our results add to the evidence of the role played by immune defences in determining survival prospects in natural populations.
4. In conclusion, our study reveals that CMI response can be considered as a good predictor of post-fledging recruitment. As far as we know, this is the first study attempting to evaluate the relationship between nestling T and post-fledging survival. Our results suggest that the potential benefits accrued by high levels of T in sibling competition during the nestling stage do not translate into increased survival.
[Show abstract][Hide abstract] ABSTRACT: The developmental rate of cuckoo embryos and their hatching size is greater than that of host species, which may require more nutrient resources in the egg and more intensive gas exchange during development. In the present study, we compared various egg characteristics of a brood parasite, the common cuckoo Cuculus canorus, and its frequent host, the great reed warbler Acrocephalus arundinaceus. As maternally-derived testosterone is known to enhance growth rate of embryos and hatchlings, cuckoo eggs are expected to contain higher concentration of testosterone than host eggs. In addition, we expected higher concentration of antioxidants in cuckoo eggs to protect embryos from oxidative stress associated with accelerated growth. Our results showed that cuckoo eggs had thicker shells and higher pore density than great reed warbler eggs. Yolk was significantly heavier in cuckoo eggs and contained higher concentrations of carotenoids and vitamin E, however, yolk androgen and immunoglobulin concentrations were lower in cuckoo eggs as compared to great reed warbler eggs. We also examined whether eggshell colour was associated to egg quality, and detected a positive association between blue-green chroma and yolk antioxidant concentration in both species, suggesting that eggshell colour reflects the antioxidant investment of the female into the eggs. Our results suggest that cuckoo females increase the size, growth rate and competitive ability of their young by providing them with more nutrients and more dietary antioxidants for embryonic development, and not through elevated yolk testosterone or antibody levels. In addition, increased porosity of cuckoo eggshells may allow embryos to develop more rapidly because of a greater capacity of gas exchange.
Full-text · Article · Feb 2010 · Journal of Avian Biology
[Show abstract][Hide abstract] ABSTRACT: Multiple male traits and displays may act in signalling sexually selected processes during courtship. Spotless starling males (Sturnus unicolor) carry green plants into their nests before egg laying, and recent studies have shown that this behaviour is related to female breeding decisions and the production of male-biased broods. Although the functional implications of this effect on females are not yet clear, data suggest that it could be mediated by female circulating hormones. Additionally, females may show higher androgen levels as a consequence of the increased female–female competition generated by the increase in male attractiveness. We tested this hypothesis using the same manipulation of green nesting material that has been previously shown to result in an increase of male attractiveness in male spotless starlings. We found that females in experimental nests increased their circulating testosterone levels during the laying period. In addition, there was an increase of social interferences in the experimental nests because of the addition of green plants. We hypothesise that testosterone may allow females to maintain their mating status when competing with other females for the preferred males. Addition of green plants also increased the variance in the levels of circulating testosterone, suggesting plasticity between females in their response to the manipulation. We propose that there is a functional link between high testosterone levels, male-biased sex ratios and female resource-holding potential in intra-sexual competition in this species.