No effect of carotenoid supplementation on phytohemagglutinin response or body condition of nestling house wrens

Carotenoids are an essential and often limiting resource in animals and play important roles in immune system function. In birds, the period shortly after hatching is an energetically demanding stage characterized by rapid growth in body size and organ systems, including the immune system. Availability of carotenoids for the growing nestlings may be of particular importance and potentially limiting at this stage of development. We tested the hypothesis that the availability of carotenoids for the embryo in the egg and in the diet of nestlings limits the condition and immune responses of nestling house wrens (Troglodytes aedon Vieillot 1809), a species with melanin-based plumage pigments. In one experiment, nestlings within females' second broods were randomly assigned to receive either a control or a lutein supplement (2008); in a second experiment, females, before their first broods, were either induced to lay additional eggs or not induced, and nestlings within both kinds of broods were supplemented as in the first experiment (2009). There were no significant effects of lutein supplementation on nestling condition or phytohemagglutinin response. There was a significant effect of lutein supplementation on nestling mass in 2008, but the difference was opposite to that predicted. Moreover, even when breeding females were stressed by inducing them to lay supernumerary eggs, lutein supplementation of nestlings had no effect on the size or condition of nestlings hatching from these eggs. These results suggest that maternally derived lutein in the egg and that provided in the diet of nestlings are not limiting to normal development and to the components of the immune system involved in the phytohemagglutinin response of nestling house wrens.     

Negligible effects of blood sampling on reproductive performance and return rates of Tree Swallows

Blood sampling is a frequently used method of collecting genetic and physiological data in natural populations, and understanding the possible impact of blood sampling on individuals and populations is important, both for the welfare of study organisms and to avoid introducing bias into analyses using bled individuals. Most studies of birds have revealed minimal negative effects of blood sampling. However, Brown and Brown (2009. Auk 126: 853–861) found that blood sampling reduced return rates of Cliff Swallows (Petrochelidon pyrrhonota), suggesting that these results are not always generalizable and that swallows (Hirundinidae) may be particularly sensitive to blood sampling. We examined the possible effects of blood sampling on the reproductive performance of female Tree Swallows (Tachycineta bicolor) and the return rates of both females and offspring in a population in New York state. To reduce the chances of Type II error, we tested 15 possible effects of blood sampling on reproductive performance and return rates using generalized linear mixed models. Overall, our results suggest that blood sampling had few negative effects on within‐year reproductive success or survival of adult females. The one exception was that bleeding nestlings had a negative effect on the number of young that fledged in broods of five or six nestlings. Bleeding did not negatively impact return rates of females or nestlings in our Tree Swallow population. Our results support those of other studies suggesting that blood sampling has few negative effects on within‐year reproductive success or survival of adult females, and reiterate the importance of systematically testing for possible effects with datasets compiled over multiple years because such effects may be impossible to detect via direct monitoring during a single breeding season.     

Effects of the parasitic botfly Philornis carinatus on nestling house wrens,Troglodytes aedon,in Costa Rica

I studied the life cycle of a botfly (Diptera: Muscidae: Philornis carinatus) and examined the effects of botfly ectoparasitism on nestling house wrens (Passeriformes: Troglodytidae: Troglodytes aedon) during three years in Costa Rica. At three study sites, I found that nestlings were relatively unaffected by botflies, in contrast to all other studies of birds infected with philornid botflies. At Monteverde, the main study site, infected chicks grew slightly slower and had slightly shorter tarsi and wing chords than uninfected chicks, but both groups fledged at similar weights. Since weight at fledging is the only growth character associated with post-fledging survivorship, botfly infections likely cost wrens little in terms of fitness. At all sites, fledging success did not differ between infected and uninfected nests. Botfly infections were more prevalent at two lower elevation sites than at the high elevation Monteverde side. Infection prevalence increased during the nesting season at all study sites, which suggests a botfly life cycle in which adult population levels increase during the wren breeding season and then decline during a dormant period when wrens are not nesting. Finally, botflies may attack chicks throughout the period before fledging, but there is no indication they locate nests before hatching. In sum, botfly parasitism on wrens appears to be benign, perhaps because the study sites are at the edge of the botfly's range or because wrens are not a preferred host.     

Plasma chemistry in booted eagle (Hieraaetus pennatus) during breeding season

Most studies that have examined raptor plasma chemistry have been conducted on birds living in captivity. In this study, we describe typical plasma chemistry values indicators of body condition in free-living Booted Eagles, Hieraaetus pennatus, from Do?ana National Park (Spain). Values are compared with those of other raptors. Mean concentrations of creatinine, uric acid and urea were lower in adults than in nestlings, while glucose, DAT and AAT were lower in nestlings than in adults. Interactions of age/sex affected plasma mean levels of creatine kinase, glucose, AAT, uric acid and urea. Adult females showed significantly lower levels of creatine kinase, uric acid and urea than adult males and nestlings. Adult males had significantly higher levels of AAT than the other groups. The lowest levels of glucose and the highest levels of uric acid were found in nestling females. We think the differences in blood parameters can be explained by differences in size of species, of individuals (because of both body condition and sexual dimorphism) and diet.     

Assessing the effects of haematophagous ectoparasites on the health of nestling birds: haematocrit vs haemoglobin levels in House Wrens parasitized by blow fly larvae

We compared haematocrits and blood haemoglobin concentrations of nestling House Wrens Troglodytes aedon in nests with relatively large numbers of haematophagous larvae of the blow fly Protocalliphora parorum (>6.4 large larvae/nestling) and nests in which exposure to larvae was severely reduced or eliminated (0–2.0 larvae/nestling). Heavily parasitized nestlings showed no reduction in haematocrit levels but a significant 28% reduction in haemoglobin levels. Previous research on avian response to chronic blood loss suggests that parasitized nestlings may show normal volumes of red blood cells as a result of a rapid production of new cells in response to blood loss and, additionally, as a result of swelling of individual cells left in the bloodstream after parasite feeding. Rapid erythropoiesis places high numbers of haemoglobin-poor, immature cells into the bloodstream which would explain the reduced haemoglobin levels of parasitized nestlings. Our results refute the conclusion that larval feeding has "little direct effect" on nestling wrens in this parasite–host system, drawn earlier by Johnson and Albrecht (1993) based on examination of haematocrits alone. Our results also strongly suggest that researchers wanting to measure effects of blood-feeding parasites on birds measure haemoglobin levels, not haematocrits.     

Fitness-related consequences of egg mass in nestling house wrens

The fitness-related consequences of egg mass, independent of confounding influences associated with parental quality, remain poorly understood for wild birds in general and for passerines in particular. We performed cross-fostering experiments to test the hypothesis that egg mass, independent of parental quality, is the primary determinant of fitness-related traits in nestling house wrens (Troglodytes aedon), an insectivorous passerine. Nestling mass was significantly correlated with the mass of the eggs from which nestlings hatched early but not late in the nestling period in early-season broods. In contrast, in late-season broods, nestling mass was correlated with egg mass until nestlings achieved asymptotic mass. Neither nestling growth nor survival to nest leaving was related to egg mass in either early- or late-season broods; however, nestlings in late-season broods grew more slowly than did nestlings in early-season broods. We propose that nestling mass and egg mass remained correlated throughout the nestling period in late-season broods because decreased arthropod food resources late in the breeding season constrain parents'' ability to provision nestlings. We conclude that female house wrens in this population trade-off clutch size for greater egg mass to maximise reproductive success in late-season broods.     

Haemoproteus spp. and Leukocytozoon spp. in a captive raptor population

Raptors are commonly infected with two blood parasites of the family Haemoproteidae, Haemoproteus spp. and Leukocytozoon spp. To determine if age or length of time in captivity influence prevalence of Haemoproteus spp. and Leukocytozoon spp. infection in captive raptors, blood samples were collected from 55 birds from April 1999 to May 2000. Blood smears were examined for parasitemia and influence of age and length of time in captivity at the time of sample collection were compared. We found juvenile and adult birds were more likely to be infected with Leukocytozoon spp. than were nestlings (P = 0.006) and birds present for > 365 days were more likely to be infected with Haemoproteus spp. and/or Leukocytozoon spp. than were birds captive for < 365 days.     

Avoidance,tolerance, and resistance to ectoparasites in nestling and adult tree swallows

We examined avoidance, tolerance, and resistance strategies of nestling and adult tree swallows Tachycineta bicolor in response to ectoparasitic blowflies Protocalliphora sialia. Tree swallows avoided settling in north‐facing nest boxes early in the breeding season. These boxes were more likely to be parasitized later in the season, suggesting that box selection may facilitate blowfly avoidance. After experimentally manipulating blowfly intensity, we found that nestlings were generally tolerant of parasitism. Parasites significantly reduced nestling blood hemoglobin but had no effect on nestling body mass, primary feather growth, age at fledging, or fledging success. Parents of parasitized nestlings did not increase their food provisioning rate to promote nestling tolerance. Adult female tree swallows demonstrated both tolerance and resistance: blowfly parasitism had no effect on adult hemoglobin and body mass, and those with higher P. sialia‐binding antibody levels had fewer blowfly larvae in their nests. Nestling antibodies were unrelated to blowfly intensity. Despite considerable variation among years, our results suggest that the costs of blowfly parasitism to nestling and adult tree swallows are modest, and limited to blood loss in nestlings. Future work should examine the effects of reduced blood hemoglobin on fledgling survival and the importance of parasite‐specific antibodies.     

Effects of captivity and testosterone on the volumes of four brain regions in the dark-eyed junco (Junco hyemalis)

This study investigates the effects of captivity and testosterone treatment on the volumes of brain regions involved in processing visual and spatial information in adult dark-eyed juncos (Junco hyemalis). We treated captive and free-living male juncos with either testosterone-filled or empty implants. Captive juncos had a smaller hippocampal formation (HF) (both in absolute volume and relative to telencephalon) than free-living birds, regardless of hormone treatment. Testosterone-treated males (both captive and free-living) had a smaller telencephalon and nucleus rotundus, but not a smaller HF or ectostriatum, than controls. We found that free-living testosterone-treated males had larger home ranges than free-living controls in agreement with earlier experiments, but we found no corresponding difference in HF volume. We discuss the implications of the effect of captivity on HF volume for past and future laboratory experiments.     

Catch-up growth in Japanese quail (Coturnix Japonica): relationships with food intake, metabolic rate and sex

The effects of early environmental conditions can profoundly affect individual development and adult phenotype. In birds, limiting resources can affect growth as nestlings, but also fitness and survival as adults. Following periods of food restriction, individuals may accelerate development, undergoing a period of rapid “catch-up” growth, in an attempt to reach the appropriate size at adulthood. Previous studies of altricial birds have shown that catch-up growth can have negative consequences in adulthood, although this has not been explored in species with different developmental strategies. Here, we investigated the effects of resource limitation and the subsequent period of catch-up growth, on the morphological and metabolic phenotype of adult Japanese quail (Coturnix japonica), a species with a precocial developmental strategy. Because males and females differ in adult body size, we also test whether food restriction had sex-specific effects. Birds that underwent food restriction early in development had muscles of similar size and functional maturity, but lower adult body mass than controls. There was no evidence of sex-specific sensitivity of food restriction on adult body mass; however, there was evidence for body size. Females fed ad lib were larger than males fed ad lib, while females subjected to food restriction were of similar size to males. Adults that had previously experienced food restriction did not have an elevated metabolic rate, suggesting that in contrast to altricial nestlings, there was no metabolic carry-over effect of catch-up growth into adulthood. While Japanese quail can undergo accelerated growth after re-feeding, timing of food restriction may be important to adult size, particularly in females. However, greater developmental flexibility compared to altricial birds may contribute to the lack of metabolic carryover effects at adulthood.     

Food restricted Tufted Puffin (Fratercula cirrhata) nestlings increase vocal activity during handling without modulating total or free corticosterone

In some species, corticosterone (CORT) appears to play a role in the control of begging behavior. Because of the potentially high costs associated with chronic elevation of CORT, it has also been proposed as a mechanism to ensure begging is an honest signal. We determined the effects of moderate food restriction (50% of high calorie treatment) on vocal behavior during handling, and on baseline levels of both total and ‘free’ unbound CORT in Tufted Puffin (Fratercula cirrhata) nestlings. Chick vocalizations during handling were similar to begging calls, and we assumed they were representative of begging behavior. We also measured total and free CORT in free-living Tufted Puffin chicks to determine if hormone levels in our experiment were comparable to natural levels. We found no effect of caloric restriction on either total or free baseline CORT, yet food-restricted nestlings vocalized more intensely during handling than chicks in the high calorie group. Mean plasma concentrations of total and free CORT in experimentally manipulated birds did not differ from levels in free-living nestlings. These results suggest that CORT does not play a role in modulating begging behavior in this species.     

Variable effects of yolk androgens on growth, survival, and immunity in eastern bluebird nestlings

Female birds allocate androgens differentially within and among clutches, and it has been suggested that this is a strategy to maximize reproductive success. Only a few studies, however, have examined the effects of yolk testosterone (T) on the growth and development of nestlings, and none have reported on the immunological effects of yolk T nor have they examined several different effects in the same nestlings. To examine the effects of yolk T on nestling eastern bluebirds, we administered two doses of exogenous T to bluebird eggs and measured the growth and immunological responsiveness in the resulting nestlings. We found that yolk T is detrimental to developing embryos, with hatching success decreasing with increasing doses of yolk T. Moderate doses of yolk T stimulated skeletal growth during the embryonic period, while high doses of yolk T resulted in nestlings that weighed more and were more mature at fledging but had a compromised T-cell immune response to phytohemagglutinin. These data suggest that the alteration of reproductive success through the allocation of yolk T is a complicated phenomenon that involves the integration of several physiological effects.     

Elevated corticosterone during egg production elicits increased maternal investment and promotes nestling growth in a wild songbird

Glucocorticoids circulating in breeding birds during egg production accumulate within eggs, and may provide a potent form of maternal effect on offspring phenotype. However, whether these steroids affect offspring development remains unclear. Here, we employed a non-invasive technique that experimentally elevated the maternal transfer of corticosterone to eggs in a wild population of house wrens. Feeding corticosterone-injected mealworms to free-living females prior to and during egg production increased the number of eggs that females produced and increased corticosterone concentrations in egg yolks. This treatment also resulted in an increase in the amount of yolk allocated to eggs. Offspring hatching from these eggs begged for food at a higher rate than control offspring and eventually attained increased prefledging body condition, a trait predictive of their probability of recruitment as breeding adults in the study population. Our results indicate that an increase in maternal glucocorticoids within the physiological range can enhance maternal investment and offspring development.     

Intraseasonal variation in immune defence,body mass and hematocrit in adult house martins Delichon urbica

The intensity of parasite infections often increases during the reproductive season of the host as a result of parasite reproduction, increased parasite transmission and increased host susceptibility. We report within‐individual variation in immune parameters, hematocrit and body mass in adult house martins Delichon urbica rearing nestlings in nests experimentally infested with house martin bugs Oeciacus hirundinis and birds rearing nestlings in initially parasite‐free nests. From first to second broods body mass and hematocrit of breeding adult house martins decreased. In contrast leucocytes and immunoglobulins became more abundant. When their nests were infested with ectoparasites adults lost more weight compared with birds raising nestlings in nests treated with pyrethrin, whereas the decrease in hematocrit was more pronounced during infection with blood parasites. Neither experimental infestation with house martin bugs nor blood parasites had a significant effect on the amount of immune defences.     

Long-term consequences of early ontogeny in free-living Great Tits Parus major

Environmental factors during early development may have profound effects on subsequent life-history traits in many bird species. In wild birds, sex-specific effects of early ontogeny on natal dispersal and future reproduction are not well understood. The objective of this work was to determine whether hatching date and pre-fledging mass and condition of free-living Great Tits Parus major have any subsequent effect on individuals’ natal dispersal and reproductive performance at first breeding. Both males and females dispersed longer distances in coniferous than in deciduous forests, while dispersal was condition-dependent only in males (heavier as nestlings dispersed farther). In females, mass and condition at pre-fledging stage correlated significantly with clutch size, but not with subsequent reproductive performance as measured by fledging success or offspring quality. In contrast, heavier males as nestlings had higher future fledging success and heavier offspring in their broods compared with those in worse condition as nestlings. The hatching date of female as well as male parents was the only parental parameter related to the number of eggs hatched at first breeding. These results indicate that pre-fledging mass and condition predict subsequent fitness components in this bird species. We suggest that sex-specific relationships between a disperser’s condition and its selectivity with respect to breeding habitat and subsequent performance need to be considered in future models of life-history evolution.     

Sex differences in DHEA and estradiol during development in a wild songbird: Jugular versus brachial plasma

Sexual differentiation of the brain has traditionally been thought to be driven by gonadal hormones, particularly testosterone (T). Recent studies in songbirds and other species have indicated that non-gonadal sex steroids may also be important. For example, dehydroepiandrosterone (DHEA) - a sex steroid precursor that can be synthesized in the adrenal glands and/or brain - can be converted into active sex steroids, such as 17β-estradiol (E₂), within the brain. Here, we examine plasma DHEA and E₂ levels in wild developing European starlings (Sturnus vulgaris), from hatch (P0) to fledging (P20). Blood samples were collected from either the brachial vein (n = 143) or the jugular vein (n = 129). In songbirds, jugular plasma is enriched with neurally-synthesized steroids and, therefore, jugular plasma is an indirect measure of the neural steroidal milieu. Interestingly, brachial DHEA levels were higher in males than females at P4. In contrast, jugular DHEA levels were higher in females than males at P0 and P10. Brachial E₂ levels were higher in males than females at P6. Surprisingly, jugular E₂ levels were not high and showed no sex differences. Also, we calculated the difference between brachial and jugular steroid levels. At several ages, jugular steroid levels were lower than brachial levels, particularly in males, suggesting greater neural metabolism of circulating DHEA and E₂ in males than females. At a few ages, jugular steroid levels were higher than brachial levels, suggesting neural secretion of DHEA or E₂ into the general circulation. Taken together, these data suggest that DHEA may play a role in brain sexual differentiation in songbirds.     

Traffic noise exposure affects telomere length in nestling house sparrows

In a consistently urbanizing world, anthropogenic noise has become almost omnipresent, and there are increasing evidence that high noise levels can have major impacts on wildlife. While the effects of anthropogenic noise exposure on adult animals have been widely studied, surprisingly, there has been little consideration of the effects of noise pollution on developing organisms. Yet, environmental conditions experienced in early life can have dramatic lifelong consequences for fitness. Here, we experimentally manipulated the acoustic environment of free-living house sparrows (Passer domesticus) breeding in nest boxes. We focused on the impact of such disturbance on nestlings’ telomere length and fledging success, as telomeres (the protective ends of chromosomes) appear to be a promising predictor of longevity. We showed that despite the absence of any obvious immediate consequences (growth and fledging success), nestlings reared under traffic noise exposure exhibited reduced telomere lengths compared with their unexposed neighbours. Although the mechanisms responsible for this effect remain to be determined, our results provide the first experimental evidence that noise alone can affect a wild vertebrate''s early-life telomere length. This suggests that noise exposure may entail important costs for developing organisms.     

Histologic, neurologic, and immunologic effects of methylmercury in captive great egrets

Captive great egret (Ardea albus) nestlings were maintained as controls or were dosed with methylmercury chloride at low (0.5), and high doses (5 mg/kg, wet weight) in fish. Low dosed birds were given methylmercury at concentrations comparable to current exposure of wild birds in the Everglades (Florida, USA). When compared with controls, low dosed birds had lower packed cell volumes, dingy feathers, increased lymphocytic cuffing in a skin test, increased bone marrow cellularity, decreased bursal wall thickness, decreased thymic lobule size, fewer lymphoid aggregates in lung, increased perivascular edema in lung, and decreased phagocytized carbon in lung. High dosed birds became severely ataxic and had severe hematologic, neurologic, and histologic changes. The most severe lesions were in immune and nervous system tissues. By comparing responses in captive and wild birds, we found that sublethal effects of mercury were detected at lower levels in captive than in wild birds, probably due to the reduced sources of variation characteristic of the highly controlled laboratory study. Conversely, thresholds for more severe changes (death, disease) occurred at lower concentrations in wild birds than in captive birds, probably because wild birds were exposed to multiple stressors. Thus caution should be used in applying lowest observed effect levels between captive and wild studies.     

Blood sampling and intravenous injections in Japanese quail (Coturnix coturnix japonica).

The suitability of five different sites (brachial, jugular, caudal tibial vein, external dorsal thoracic vein and the heart) were examined for blood sampling and intravenous injections in Japanese quail. In terms of safety, ease of collection, repeated collections or injections, the jugular vein was found to be the most suitable.     

Hatching asynchrony and growth trade‐offs within domesticated and wild zebra finch,Taeniopygia guttata,broods

The Australian zebra finch, Taeniopygia guttata, is a widely used model organism, yet few studies have compared domesticated and wild birds with the aim of examining its relevance as an evolutionary model species. Domestic and wild broods hatch over approximately 4 and 2 days, respectively, which is important given that nestlings can fledge after as little as 12 days, although 16–18 days is common. We aimed to evaluate the extent to which the greater hatching asynchrony in domestic stock may effect reproductive success through greater variance in size hierarchies, variance in within‐brood growth rates, and partial brood mortality. Therefore, by simultaneously controlling brood sizes and experimentally manipulating hatching intervals in both domesticated and wild birds, we investigated the consequences of hatching intervals for fledging success and nestling growth patterns, as well as trade‐offs. Fledging success was similarly high in domestic and wild broods of either hatching pattern. Nonetheless, between‐brood analyses revealed that domestic nestlings had significantly higher masses, larger skeletal characters, and longer wings than their wild counterparts, although wild nestlings had comparable wing lengths at the pre‐fledging stage. Moreover, within‐brood analyses revealed only negligible differences between domestic and wild nestlings, and larger effects of hatching order and hatching pattern. Therefore, despite significant differences in the hatching intervals, and the ultimate size achieved by nestlings, the domestication process does not appear to have significantly altered nestling growth trade‐offs. The present study provides reassuring evidence that studies involving domesticated zebra finches, or other domesticated model organisms, may provide reasonable adaptive explanations in behavioural and evolutionary ecology. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 763–773.