Bird Nestlings Research Articles

Body condition of Little Egret Egretta garzetta nestlings in relation to hatching order in a southern Tunisian breeding colony

The effect of asynchronous hatching on nestling health and condition in ardeids is still in need of empirical evidence from populations living in different environmental conditions. Using morphometric and hematologic data from Little Egret Egretta garzetta nestlings in a Tunisian breeding colony, we assessed the relationship between hatching order and nestling condition, while accounting for the effects of brood size, age and hatching date. Our results showed that the youngest nestlings had lower values of hematocrit and body condition index but higher levels of fluctuating asymmetry compared with their older siblings. These trends seem to stem from increased nutritional stress experienced by younger nestlings who would have received less food from their parents than their siblings due to their less competitive nature. Additional constraints during the rearing period, such as possible injuries resulting from conflicts with siblings and the energy cost of thermoregulation, may also have contributed to the deterioration of the condition of last nestlings. Overall, our findings provide empirical evidence of the short-term repercussions of asynchronous hatching in a North African population of Little Egrets. They also highlight the great complexity of mechanisms by which asynchronous hatching may affect body condition and health of bird nestlings.

Carotenoid coloration and health status of urban Eurasian kestrels (Falco tinnunculus).

As the world experiences rapid urban expansion, natural landscapes are being transformed into cities at an alarming rate. Consequently, urbanization is identified as one of the biggest environmental challenges of our time, yet we lack a clear understanding of how urbanization affects free-living organisms. Urbanization leads to habitat fragmentation and increased impervious surfaces affecting for example availability and quality of food. Urbanization is also associated with increased pollution levels that can affect organisms directly, via ecophysiological constraints and indirectly by disrupting trophic interactions in multi-species networks. Birds are highly mobile, while an individual is not necessarily exposed to urban stressors around the clock, but nestlings of altricial birds are. Such a city-dwelling species with a long nestling phase is the Eurasian kestrel (Falco tinnunculus) in Vienna, Austria, which forage on a diverse diet differing in composition from rural habitats. Furthermore, prey items vary in nutritional value and contents of micronutrients like carotenoids, which might impact the nestlings’ health. Carotenoids are pigments that are incorporated into integument tissues but also have antioxidant and immunostimulatory capacity, resulting in a trade-off between these functions. In nestlings these pigments function in parent-offspring communication or sibling competition by advertising an individual’s physical or physiological condition. Anthropogenic disturbance and pollutants could have disruptive effects on the coloration of these traits. In this study, we measured carotenoid based coloration and other indicators of individual health (body condition and susceptibility to the ectoparasite Carnus hemapterus) of 154 nestling kestrels (n = 91 nests) along an urban gradient from 2010 to 2015. We found skin yellowness of nestlings from nest-sites in the city-center to be least pronounced. This result might indicate that inner-city nestlings are strongly affected by urban stressors and depleted their stores of dietary carotenoids for health-related functions rather than coloration. In addition, skin yellowness intensified with age and was stronger pronounced in earlier nests. Since the immune system of nestlings is still developing, younger chicks might need more antioxidants to combat environmental stress. Additionally, parasite infection intensity was highest in nestlings with less intense skin yellowness (paler or less yellow pigmented integuments) and in earlier nests of the season. In combination with results from previous studies, our findings provide further support for the low quality of the inner-city habitat, both in terms of productivity and individual health.

Multi-Element Analysis of Blood Samples in a Passerine Species: Excesses and Deficiencies of Trace Elements in an Urbanization Study

Urbanization is a growing phenomenon characterized by a complete restructuring of natural areas. In urban bird populations, a reduced offspring survival and body condition and an overall lower breeding success are often observed compared to populations inhabiting more natural habitats. Higher pollution levels and poorer quality of natural resources in cities are two environmental factors frequently mentioned in the literature to explain the differences between urban and non-urban populations. Pollution and poor quality of food may lead to an excess of non-essential elements such as Pb or Cd or to deficiencies of essential elements such as Cu or Zn, which may explain some of the impacts, notably on immunity, observed in urbanization studies. The present study compared the breeding parameters, brood body mass and condition, and haptoglobin levels, a marker of inflammatory immunity, in two urban and two forest populations of Great tits in Eastern France, together with a multi-element analysis (25 non-essential and essential trace elements) of blood samples from 13-day-old nestlings from the four populations. The concentration of NO2, a gaseous pollutant typical of urban pollution, was also measured. The NO2 concentrations were significantly higher in the urban areas, but no association with biological variables was detected. Non-essential metals were undetectable in the plasma of the birds from both habitats, except Pb, whose concentrations, however, did not differ between the urban and forest birds. A positive relationship was found between the plasmatic richness in essential elements (as assessed from the coordinates of the first axis of a PCA including 12 elements) and the average brood body mass and condition. We suggest that lower quality resources or/and a higher metabolic demand may be a causal mechanism for the reduced body condition often observed in urban bird nestlings. Finally, our exploratory study could promote more mechanistic experiments (e.g. supplementation) to explain the negative effect of urban conditions on bird populations.

Pre-mining trace element and radiation exposure to biota from a breccia pipe uranium mine in the Grand Canyon (Arizona, USA) watershed.

The risks to wildlife and humans from uranium (U) mining in the Grand Canyon watershed are largely unknown. In addition to U, other co-occurring ore constituents contribute to risks to biological receptors depending on their toxicological profiles. This study characterizes the pre-mining concentrations of total arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), thallium (Tl), U, and zinc (Zn); radiation levels; and histopathology in biota (vegetation, invertebrates, amphibians, birds, and mammals) at the Canyon Mine. Gross alpha levels were below the reporting limit (4 pCi/g) in all samples, and gross beta levels were indicative of background in vegetation (<10-17 pCi/g) and rodents (<10-43.5 pCi/g). Concentrations of U, Tl, Pb, Ni, Cu, and As in vegetation downwind from the mine were likely the result of aeolian transport. Chemical concentrations in rodents and terrestrial invertebrates indicate that surface disturbance during mine construction has not resulted in statistically significant spatial differences in fauna concentrations adjacent to the mine. Chemical concentrations in egg contents and nestlings of non-aquatic birds were less than method quantification limits or did not exceed toxicity thresholds. Bioaccumulation of As, Pb, Se, Tl, and U was evident in Western spadefoot (Spea multiplicata) tadpoles from the mine containment pond; concentrations of As (28.9-31.4μg/g) and Se (5.81-7.20μg/g) exceeded toxicity values and were significantly greater than in tadpoles from a nearby water source. Continued evaluation of As and Se in biota inhabiting and forging in the mine containment pond is warranted as mining progresses.

The significance of seed food in chick development re‐evaluated by tracking day‐to‐day dietary variation in the nestlings of a granivorous passerine

The dietary adjustment of nestlings of granivorous birds to a seed diet and the different morphological characteristics of ingested food have rarely been examined in natural conditions. It has been suggested that the provision of cereal grains to nestlings of some seed‐eating bird species in modern agroecosytems is the result of poor food conditions after agricultural intensification. We analysed the abundance of invertebrate prey in the main foraging habitat of parent birds, daily changes (from hatching to fledging) in the efficiency of cereal seed digestion, and the dietary characteristics, diet composition and prey type delivered to nestlings of the Yellowhammer Emberiza citrinella. Analysis of faecal sacs from nests located in breeding habitat with an abundant invertebrate fauna revealed no relationship between the proportion of cereal seeds in the diet of nestlings and the food supply in the main foraging sites of the parents. Neonate nestlings (1 day old) exclusively received weakly chitinized invertebrate prey (arachnids and flies), but from the second day of life the nestlings were fed a variety of highly chitinized invertebrate prey, the percentage biomass of which did not change for the remainder of the nesting period. Cereal grains started to be delivered to 3‐day‐old nestlings and were already efficiently digested, and the percentage biomass of this food type increased progressively with nestling age. We suggest that the provisioning of cereal grains to nestlings is not forced by external factors, such as modern agricultural intensification; rather, it is an intentional behaviour of parent birds aimed at achieving physiological adjustment to seed food in the early stages of ontogeny.

Decoding colouration of begging traits by the experimental addition of the appetite enhancer cyproheptadine hydrochloride in magpiePica picanestlings

The colouration of some traits in nestlings of altricial birds may influence parental food allocation as it may reflect physical condition or hunger. There is increasing evidence of the relationship between colouration of begging traits and nestling performance. However, evidence of the influence of hunger level on nestling colouration is scarce, mainly because of difficulty of distinguishing between the effects of physical condition and hunger levels. Here, we used the appetite stimulant cyproheptadine hydrochloride to increase the sensation of hunger of magpiePica picanestlings for eight days and assessed the effect on the colouration of rictal flanges, mouth and body skin. We found that nestlings administered with cyproheptadine had flanges more conspicuous (chromatic visual contrast), more UV coloured and less yellow coloured than their control nestmates. Conversely, mouths of experimental nestlings were more yellow coloured and less UV coloured than controls. Our pharmacological experiment affected the strength of the relationship between body mass and some colour components of body skin (chromatic and achromatic visual contrasts, UV–chroma and yellow–chroma) and of rictal flanges (chromatic visual contrasts, UV–chroma and yellow–chroma), but not for mouth colouration. These results taken together suggest that the effect of the cyproheptadine on nestling colourations is probably mediated by an increase in hunger levels of nestlings for rictal flanges and body skin colourations, and by an increase in physical condition in the case of mouth coloration.

Amphibian and Reptilian Inventories Augmented by Sampling at Heronries

&#x0D; &#x0D; &#x0D; &#x0D; An alternate method for supporting amphibian and reptilian inventory was tested. This experimental method involved the collection of regurgitated food from water bird nestlings from a total of 10 heronries: four mixed-species and six single-species heronries in Gujarat State, India, during 1997 to 1999. We verified the presence of twelve species of amphibians, and twelve species of reptiles were recovered intact.&#x0D; Various methods are used to evaluate the diversity of amphibians and reptiles, many of which are resource-dependent in terms of both time and money (e.g., Heyer et al. 1994). The verification process in such diversity surveys generally requires the collection of voucher specimens for establishing the credibility of the work (Dubois and Nemesio 2007; Funk et al. 2005). Vouchers also facilitate further taxonomic studies and the identification of cryptic species, especially when species complexes occupy the area being surveyed. The collection of specimens requires permission from the appropriate government authority. Because relevant authorities in India are often hardcore believers of the philosophy of “Jiv Daya” (a Jainist concept involving compassion for all beings) and unaware of the need for voucher specimens, acquisition of permits to collect in protected areas (sanctuaries and national parks), even for studies of biodiversity and environmental assessments is extremely difficult. Even when permission for voucher collection is granted, strict time constraints are imposed. These render surveys of large areas almost impossible, particularly because vouchers ideally involve a series of specimens of various species (Goodman and Lanyon 1994) and collection methods often are very time consuming. Consequently, methods that are less time-consuming and less expensive are needed. Herein, we test one such alternative.&#x0D; &#x0D; &#x0D; &#x0D;

Parent-Absent Begging in Barn Swallow Broods: Causes of Individual Variation and Effects on Sibling Interactions and Food Allocation

Altricial offspring solicit parental care using complex begging displays. Although such solicitations are mainly performed towards parents, nestlings of several birds often beg when parents are not at the nest. This parent-absent begging (PAB) has been interpreted as a mistake in correctly detecting parental arrival, but it may also reliably signal individual need to nest mates, potentially affecting intra-brood competition for food. Here, we focused on the proximate factors that may determine frequency and intensity of PAB, including brood size and sex ratio, as well as individual age, sex and body mass, in natural barn swallow (Hirundo rustica) broods, under conditions of normal and experimentally reduced food intake. We also investigated the relationship between PAB and begging intensity at parental arrival and food intake in the two different experimental conditions. The frequency of PAB was larger after food deprivation than before, indicating that PAB reliably reflects hunger level. In addition, nestlings increased their own begging intensity upon parental arrival after performing PAB. Concomitantly, siblings decreased begging effort, irrespective of sex or body mass, but this occurred only when nestlings were normally fed, suggesting that PAB diminishes scrambling for food by nest mates. Finally, such a reciprocal begging modulation resulted in a larger chance of obtaining food at the subsequent feeding event for nestlings performing PAB under normal food provisioning. Within-brood signalling in the absence of parents can therefore play an important role in determining competitive strategies among siblings and affecting parental decisions on food allocation in altricial broods.

Testing for associations between hematozoa infection and mercury in wading bird nestlings.

Several wading bird species in the southeastern US have a history of infection by hematozoa/avian malaria as well as mercury accumulation through their diet, and thus may be exposed to two, generally sublethal, yet chronic, stressors. We analyzed nestling wading birds (n = 171) of varying size and trophic position from the southeastern US, and a smaller sample (n = 23) of older, free-ranging birds, to look for potential interrelationships between infection by hematozoa and mercury (Hg) uptake. Only one nestling was PCR positive for hematozoa (Plasmodium/Haemoproteus) whereas nine (39%) of the older wading birds were positive. Sequencing indicated that both nestling and adult positives were infected with Plasmodium. Given the low infection rate of the nestlings, there was no association between Hg and malaria. The older birds exhibited a possible malaria/Hg association, but it may be confounded by their greater potential exposure period and large-scale movements.

Gizzard Mass Dynamics of Nestling Rooks Corvus Frugilegus

Developmental changes of the gizzard have rarely been studied in nestlings of non-domesticated birds or under natural conditions. Because nestlings would have variable amounts of stomach contents, we wanted to discover whether in natural conditions gizzard developmental changes are dependent on digesta mass. We examined the mass of gizzard and digesta in 56 nestling Rooks Corvus frugilegus aged between 1 and 13 days old. We found that gizzard mass increased nearly nine-fold, from an average of 1.25 g to 10.85 g. Gizzard mass expressed as a proportion of body weight significantly decreased with the age of nestlings. In hatchlings, the median ratio of gizzard mass to body weight was 18.4%; in 13-day old nestlings this value was only 5.8%. Tarsus length, a poor predictor of gizzard mass, explained 61% of its total variance. Nestlings (regardless of their age) without digesta or with small volumes of digesta had statistically significantly smaller gizzards (expressed as ratio of gizzard mass to body weight) than did nestlings with full gizzards, which suggest a rapid response of gizzard volume and musculature to variable food intake during post-hatch development.

Vocal begging and locomotor activity are modulated independently in Bank Swallow (Riparia riparia) nestlings

ABSTRACT Nestlings of birds breeding in closed nests compete for food by both vocal begging and competing for a position near the nest entrance (locomotor activity). The latter strategy can be particularly effective in nests with long entrance tunnels, where nestlings can intercept feedings from incoming parents. However, little is known about whether the intensity of locomotor activity is related to food availability in the same way as the intensity of vocal begging. We hand-fed Bank Swallow nestlings (Riparia riparia) in the laboratory under four feeding regimes: without restriction (AL), or facing different levels of food restriction (in order of increasing degree: FR1, FR2, FR3). Compared with group AL, the intensity of vocal begging was elevated in group FR1 and did not increase further in the FR3 group, whereas only the FR3 nestlings showed higher locomotor activity (quantified as the frequency of crawling to the nest tunnel). The FR3 group was also the only group where reduced food intake slowed wi...

Diet Composition of the Demoiselle Crane (Anthropoides virgo) Migrating Through Lakki Marwat, Pakistan

Demoiselle Cranes (A nthropoides virgo) migrate through Pakistan between their breeding and wintering grounds. We undertook macro and micro-analyses of 16 gizzards and 35 faecal samples of this elegant bird during its stopovers in the Lakki Marwat area of Khyber Pakhtunkhwa Province, Pakistan. Analysis of 16 gizzards and 16 faecal samples of spring season showed that the bird was predominantly vegetarian and fed on cultivated crops ( viz: wheat, sorghum, chickpea, Egyptian clover and garlic) and wild flora ( viz: wild onion, beard grass and bur clover). Similarly, analysis of 19 faecal samples collected during the autumn revealed the presence of cultivated crops ( viz: chickpea, mustard and spinach) and wild plant species ( viz: wild onion, bur clover, salt cedar, beard grass and alkali seep weed). The Demoiselle Crane supplemented its diet with animal matters (ranging from 3 to 20%) derived from invertebrates belonging to Phylum Arthropoda (Order Pauropodina and Order Plecoptera) and vertebrate species i.e. tadpoles, Mus spp. and nestlings of birds. In addition, large quantities of grit composed of small stones and quartz crystals were found in the gizzards and faecal samples. This study provides information on the important flora and fauna that contribute to the diet of migratory Demoiselle Cranes. This aids strategies to conserve and protect the natural habitats from intensive anthropogenic use and livestock grazing, and helps to sustain and enhance numbers of this avian species.

Plasma concentrations of organohalogenated pollutants in predatory bird nestlings: Associations to growth rate and dietary tracers

The extent to which persistent organic pollutants (POPs) with different physicochemical properties originated from the food (dietary input) was assessed in raptor nestlings. Lipophilic polychlorinated biphenyl (PCB) 153, 1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE), and hexachlorobenzene (HCB), and protein-bound perfluorooctane sulfonate (PFOS), were measured repeatedly in blood plasma of individual goshawk (Accipiter gentilis) and white-tailed eagle (Haliaeetus albicilla) nestlings, 1 to 3 wk after hatching and near fledging. Maternally derived POPs dilute as nestlings grow (growth dilution), and increasing plasma concentrations would indicate dietary input. First, plasma concentrations given no dietary input were estimated, and concentrations of p,p'-DDE, HCB, and notably PFOS were significantly higher than predicted from a growth-dilution scenario (approximately 1.5-fold to 2.5-fold higher; p < 0.001). In contrast, PCB 153 declined in both species, although concentrations were still higher than predicted in white-tailed eagle nestlings (p < 0.05). Second, the relationships between plasma POP concentrations and trophic position (δ(15) N) and dietary carbon source (δ(13) C) were analyzed, controlling for growth rate. Both δ(15) N and δ(13) C (measured in body feathers) were significantly associated to the accumulation of most POPs, except PFOS. In conclusion, pollutant data acquired in plasma of nestling raptors should be interpreted and further investigated in the light of individual feeding ecology, and the use of raptor nestlings as sentinels for POP monitoring could be optimized by correcting for different factors such as body condition, brood size, and age.

Multi-Level Determinants of Parasitic Fly Infection in Forest Passerines

The study of myiasis is important because they may cause problems to the livestock industry, public health, or wildlife conservation. The ecology of parasitic dipterans that cause myiasis is singular, as they actively seek their hosts over relatively long distances. However, studies that address the determinants of myiasis dynamics are very scarce. The genus Philornis include species that may be excellent models to study myiasis ecology, as they exclusively parasitize bird nestlings, which stay in their nests until they are fully fledged, and larvae remain at the point of entry until the parasitic stage is over, thus allowing the collection of sequential individual-level infection data from virtually all the hosts present at a particular area. Here we offer a stratified multi-level analysis of longitudinal data of Philornis torquans parasitism in replicated forest bird communities of central Argentina. Using Generalized Linear Models and Generalized Linear Mixed Models and an information theory approach for model selection, we conducted four groups of analyses, each with a different study unit, the individual, the brood, the community at a given week, and the community at a given year. The response variable was larval abundance per nestling or mean abundance per nestling. At each level, models included the variables of interest of that particular level, and also potential confounders and effect modifiers of higher levels. We found associations of large magnitude at all levels, but only few variables truly governed the dynamics of this parasite. At the individual level, the infection was determined by the species and the age of the host. The main driver of parasite abundance at the microhabitat level was the average height of the forest, and at the community level, the density of hosts and prior rainfall. This multi-level approach contributed to a better understanding of the ecology of myiasis.

Ecological and spatial factors drive intra- and interspecific variation in exposure of subarctic predatory bird nestlings to persistent organic pollutants

Top predators in northern ecosystems may suffer from exposure to persistent organic pollutants (POPs) as this exposure may synergistically interact with already elevated natural stress in these ecosystems. In the present study, we aimed at identifying biological (sex, body condition), ecological (dietary carbon source, trophic level) and spatial factors (local habitat, regional nest location) that may influence intra- and interspecific variation in exposure of subarctic predatory bird nestlings to polychlorinated biphenyl 153 (CB 153), polybrominated diphenyl ether 47 (BDE 47), dichlorodiphenyldichloroethylene (p,p′-DDE) and hexachlorobenzene (HCB). During three breeding seasons (2008–2010), we sampled body feathers from fully-grown nestlings of three ecologically distinct predatory bird species in subarctic Norway: Northern Goshawk (Accipiter gentilis), White-tailed Eagle (Haliaeetus albicilla) and Golden Eagle (Aquila chrysaetos). The present study analysed, for the first time, body feathers for both POPs and carbon (δ13C) and nitrogen (δ15N) stable isotopes, thus integrating the dietary carbon source, trophic level and POP exposure for the larger part of the nestling stage.Intraspecific variation in exposure was driven by a combination of ecological and spatial factors, often different for individual compounds. In addition, combinations for individual compounds differed among species. Trophic level and local habitat were the predominant predictors for CB 153, p,p′-DDE and BDE 47, indicating their biomagnification and decreasing levels according to coast>fjord>inland. Variation in exposure may also have been driven by inter-annual variation arisen from primary sources (e.g. p,p′-DDE) and/or possible revolatilisation from secondary sources (e.g. HCB). Interspecific differences in POP exposure were best explained by a combination of trophic level (biomagnification), dietary carbon source (food chain discrimination) and regional nest location (historical POP contamination).In conclusion, the combined analysis of POPs and stable isotopes in body feathers from fully-grown nestlings has identified ecological and spatial factors that may drive POP exposure over the larger part of the nestling stage. This methodological approach further promotes the promising use of nestling predatory bird body feathers as a non-destructive sampling strategy to integrate various toxicological and ecological proxies.

Increased exposure to yolk testosterone has feminizing effects in chickens, Gallus gallus domesticus

Competing for food by altricial and semiprecocial bird nestlings is a behaviour well known for its sensitivity to maternal androgens during prenatal development. Whether a similar effect is present in precocial species that do not beg is less well known. We therefore increased yolk testosterone levels within the physiological range at the onset of incubation to study its effects on food competition behaviour in the domestic chicken, Gallus gallus domesticus. We found an increase in competitiveness in testosterone-treated male domestic chicks, raising their level to that of the females. This is in line with the decrease in circulating plasma levels of males in the direction of the levels in females, and the overall decrease in androgen receptor densities after prenatal treatment as found previously. Hormones are known to have long-lasting organizing effects on behaviour and to affect sexual differentiation in vertebrates. Although research into hormone-mediated maternal effects has been productive, only a few studies describe (the ambiguous) effects into adulthood. Therefore we followed our animals into adulthood and recorded androgen-dependent social behaviour and secondary sexual characteristics, body mass and circulating plasma testosterone levels and checked whether these variables were treatment dependent. Treatment had a near significant effect on comb colour (both brightness and chroma). Again treatment caused a shift towards a more female-like phenotype. This suggests that, in contrast to earlier suggestions, maternal androgens may interact with (but not disrupt) sexual differentiation of brain and behaviour and the development of secondary sexual characteristics.

Climate variability affects the impact of parasitic flies on Argentinean forest birds

The genus Philornis (Diptera: Muscidae) comprises Neotropical parasitic flies that parasitize bird nestlings while in their larval stage. The ecology of most species of these parasitic flies is largely unknown. Here, we contribute with data that shed some light on the environmental factors that are associated with variations in parasitism intensity of Philornis torquans, and examine whether increased intensity is followed by greater probability of mortality or reduced nestling growth. Intensive examination of nestlings of the bird community present in a 30 ha area was carried out weekly along two breeding seasons in Santa Fe, Argentina. Some nestlings of the most frequently parasitized bird species were followed twice a week, from hatching to fledging, to assess the impact of the parasites. High average maximum temperature and increased rainfall were significantly positively correlated with mean Philornis intensity. In turn, heavily parasitized nestlings were more likely to die: 10 larvae doubled the chances of mortality, and growth was affected in those that survived. The greater precipitation and warmer weather predicted for some areas of South America pose a potential impact on nestlings via this parasitism, and consequently on the population dynamics of native birds.

Harvestmen as predators of bird nestlings

Abstract We report the first confirmed cases of harvestmen (Opiliones) feeding upon live vertebrates. In June and July of 2007, in two independent studies of the ecology of Swainson's warblers (Limnothlypis swainsonii Audubon) in Arkansas and North Carolina, we recorded predation of nestlings at two separate nests by harvestmen. Both events were nocturnal, involved relatively young and dependent nestlings, and contributed to or resulted in the death of one or more nestlings. One event involved a group of at least four harvestmen with one to four individuals feeding upon a brown-headed cowbird (Molothrus ater) nestling at one time, and the other involved up to two harvestmen present at the nest, but only one individual fed upon the two Swainson's warbler nestlings.

Sibling Competition and Conspicuousness of Nestling Gapes in Altricial Birds: A Comparative Study

BackgroundNestlings of altricial birds capture parents' attention through conspicuous visual displays, including exposure of their gape coloration which informs parents about their level of need, competitive ability or health; information that parents use for deciding food allocation among their offspring. Thus, because nestlings compete with nest mates for parental care, nestling conspicuousness is expected to increase with level of sibling competition along bird phylogeny.Methodology/Principal FindingsWe test this prediction by jointly using information of brood reduction, clutch size and duration of nestling period as proxies for intensity of sibling competition, and visual models that assess detectability of nestlings by adult birds. As predicted, we found a positive association between nestling conspicuousness and intensity of brood reduction, while clutch size and duration of nestling period did not enter in the best models. Level of brood reduction was positively related with the achromatic component of nestling conspicuousness and body mass was negatively related with the chromatic component.ConclusionsThese associations are in agreement with the hypothesis that sibling competition for parental attention has driven the evolution of visual nestling conspicuousness in a context of parent-offspring communication in altricial birds.

Genetic variation in the invasive avian parasite, Philornis downsi (Diptera, Muscidae) on the Galápagos archipelago

BackgroundUnderstanding the dispersal and genetic structure of invasive insects across islands is important for designing management plans that are appropriate at spatial and temporal scales. For invasive parasites, population dynamics are largely determined by the distribution and density of their host species. The introduced parasitic fly, Philornis downsi, parasitises nestlings of endemic birds on all major islands of the Galápagos archipelago. The fly's high mortality and fitness impacts are of conservation concern for vulnerable and declining species of Darwin's finches. Using microsatellite data in Bayesian clustering and landscape genetic analyses, we examine gene flow and dispersal in P. downsi between three islands and across habitats (highlands, lowlands) and examine for the presence of population bottlenecks. We also examine variation at the mitochondrial gene CO1 across islands to establish if cryptic species were present.ResultsBoth the mitochondrial and microsatellite data were consistent with there being a single species across islands. We found low genetic differentiation between islands and strong evidence for inter-island gene flow, or shared recent ancestry among individuals. Landscape genetic analysis identified two genetic clusters: one encompassing Santa Cruz and Isabela, and one on Floreana Island. There was no evidence of genetic differentiation between habitats and molecular variance was mainly attributable to within individuals. The combined P. downsi population was found to have undergone a population bottleneck.ConclusionPhilornis downsi populations have high connectivity within and between islands, with low levels of genetic differentiation between Floreana and the other two islands examined. The genetic bottleneck found across islands suggests there was a small founding population or few introduction events of P. downsi. The high dispersal capacity and wide habitat use of P. downsi highlights the significant threat that this parasite poses to the Galápagos avifauna. Our findings are relevant for assessing the viability of methods to control P. downsi on Galápagos, such as the sterile insect technique.