Wild Seabird Research Articles

Micro-evolutionary response of spring migration timing in a wild seabird.

In the context of rapid climate change, phenological advance is a key adaptation for which evidence is accumulating across taxa. Among vertebrates, phenotypic plasticity is known to underlie most of this phenological change, while evidence for micro-evolution is very limited and challenging to obtain. In this study, we quantified phenotypic and genetic trends in timing of spring migration using 8,032 dates of arrival at the breeding grounds obtained from observations on 1,715 individual common terns (Sterna hirundo) monitored across 27 years, and tested whether these trends were consistent with predictions of a micro-evolutionary response to selection. We observed a strong phenotypic advance of 9.3 days in arrival date, of which c. 5% was accounted for by an advance in breeding values. The Breeder's equation and Robertson's Secondary Theorem of Selection predicted qualitatively similar evolutionary responses to selection, and these theoretical predictions were largely consistent with our estimated genetic pattern. Overall, our study provides rare evidence for micro-evolution underlying (part of) an adaptive response to climate change in the wild, and illustrates how a combination of adaptive micro-evolution and phenotypic plasticity facilitated a shift towards earlier spring migration in this free-living population of common terns.

Temporal change in the contribution of immigration to population growth in a wild seabird experiencing rapid population decline

The source–sink paradigm predicts that populations in poorer‐quality habitats (‘sinks') persist due to continued immigration from more‐productive areas (‘sources'). However, this categorisation of populations assumes that habitat quality is fixed through time. Globally, we are in an era of wide‐spread habitat degradation, and consequently there is a pressing need to examine dispersal dynamics in relation to local population change. We used an integrated population model to quantify immigration dynamics in a long‐lived colonial seabird, the black‐legged kittiwakeRissa tridactyla, that is classified as globally ‘Vulnerable'. We then used a transient life table response experiment to evaluate the contribution of temporal variation in vital rates, immigration rates and population structure to realised population growth. Finally, we used a simulation analysis to examine the importance of immigration to population dynamics. We show that the contribution of immigration changed as the population declined. This study demonstrates that immigration is unlikely to maintain vulnerable sink populations indefinitely, emphasising the need for temporal analyses of dispersal to identify shifts that may have dramatic consequences for population viability.

The quantitative genetics of fitness in a wild seabird.

ABSTRACTAdditive genetic variance in fitness is a prerequisite for adaptive evolution, as a trait must be genetically correlated with fitness to evolve. Despite its relevance, additive genetic variance in fitness has not often been estimated in nature. Here, we investigate additive genetic variance in lifetime and annual fitness components in common terns (Sterna hirundo). Using 28 years of data comprising approximately 6000 pedigreed individuals, we find that additive genetic variances in the zero‐inflated and Poisson components of lifetime fitness were effectively zero but estimated with high uncertainty. Similarly, additive genetic variances in adult annual reproductive success and survival did not differ from zero but were again associated with high uncertainty. Simulations suggested that we would be able to detect additive genetic variances as low as 0.05 for the zero‐inflated component of fitness but not for the Poisson component, for which adequate statistical power would require approximately two more decades (four tern generations) of data collection. As such, our study suggests heritable variance in common tern fitness to be rather low if not zero, shows how studying the quantitative genetics of fitness in natural populations remains challenging, and highlights the importance of maintaining long‐term individual‐based studies of natural populations.

Occurrence and Quantification of Antimicrobial Resistance Genes in the Gastrointestinal Microbiome of Two Wild Seabird Species With Contrasting Behaviors

Antimicrobial resistance genes (ARGs) are environmental pollutants and anthropization indicators. We evaluated human interference in the marine ecosystem through the ocurrence and quantification (real-time PCRs) of 21 plasmid-mediated ARGs in enema samples of 25 wild seabirds, upon admission into rehabilitation: kelp gull (Larus dominicanus, n = 14) and Magellanic penguin (Spheniscus magellanicus, n = 11). Overall, higher resistance values were observed in kelp gulls (non-migratory coastal synanthropic) in comparison with Magellanic penguins (migratory pelagic non-synanthropic). There were significant differences between species (respectively, kelp gull and Magellanic penguin): ARGs occurrence (blaTEM [p = 0.032]; tetM [p = 0.015]; tetA [p = 0.003]; and sulII [p = 0.007]), mean number of ARGs per sample (p = 0.031), ARGs mean load percentage (aadA [p = 0.045], tetA [p = 0.031], tetM [p = 0.016], blaTEM [p = 0.032], sulII [p = 0.008]), percentage of genes conferring resistance to an antimicrobial class (betalactams [p = 0.036] and sulfonamides [p = 0.033]), mean number of genes conferring resistance to one or more antimicrobial classes (p = 0.024]), percentage of multiresistant microbiomes (p = 0.032), and clustering (p = 0.006). These differences are likely due to these species' contrasting biology and ecology - key factors in the epidemiology of ARGs in seabirds. Additionally, this is the first report of mecA in seabirds in the Americas. Further studies are necessary to clarify the occurrence and diversity of ARGs in seabirds, and their role as potential sources of infection and dispersal within the One Health chain of ARGs.

Telomere length is heritable and genetically correlated with lifespan in a wild bird.

Telomeres are protective caps at the end of eukaryotic chromosomes that shorten with age and in response to stressful or resource-demanding conditions. Their length predicts individual health and lifespan across a wide range of animals, but whether the observed positive association between telomere length and lifespan is environmentally induced, or set at conception due to a shared genetic basis, has not been tested in wild animals. We applied quantitative genetic "animal models" to longitudinal telomere measurements collected over a 10-year period from individuals of a wild seabird (common tern; Sterna hirundo) with known pedigree. We found no variation in telomere shortening with age among individuals at the phenotypic and genetic level, and only a small permanent environmental effect on adult telomere length. Instead, we found telomere length to be highly heritable and strongly positively genetically correlated with lifespan. Such heritable differences between individuals that are set at conception may present a hitherto underappreciated component of variation in somatic state.

Seabirds as anthropization indicators in two different tropical biotopes: A One Health approach to the issue of antimicrobial resistance genes pollution in oceanic islands

Antimicrobial resistance is a quintessential One Health issue, among the most serious 21st century global threats to human health. Seabirds may act as sentinels of natural and anthropogenic changes in the marine ecosystem health, including pollution by antimicrobial resistance genes (ARGs). We used real time PCR to identify and quantify 22 plasmid-mediated ARGs in the gastrointestinal microbiome of six wild seabird species, comparing an anthropized (Fernando de Noronha Archipelago - FNA) and a pristine biotope (Rocas Atoll - ROA), Brazil. Of 257 birds, 218 (84.8%) were positive to at least one ARG. ARG classes encoding resistance to tetracyclines (75.1%), quinolones (10.5%) and phenicols (10.5%) were the most prevalent, with tetracyclines significantly greater than the remaining classes (p < 0.05). Genes tet(S) (29.2%), tet(A) (28.8%), and tet(B) (24.9%) were the most commonly found and had a significantly greater prevalence when compared to the remaining ARGs (p < 0.05). The anthropized biotope presented statistically significant higher prevalence of sulfonamide- and quinolone-encoding ARGs in comparison with the pristine (respectively, p = 0.01 and p = 0.03), and higher sulII gene prevalence (p = 0.04), consistent with anthropogenic pressure. Migratory species (only present in ROA) showed statistically significant higher mcr-1 (polymyxins) and blaTEM (betalactam) prevalences (respectively, p = 0.009 and p = 0.02), and mcr-1 percentage load (p = 0.0079) in comparison with non-migratory. To our knowledge, this is the largest ARGs survey based on direct detection and quantification in seabirds worldwide, and the first to evaluate non-synanthropic species in oceanic islands. This is the first detection of mcr-1 in wild free-ranging seabirds in Brazil and in free-ranging migratory non-synanthropic seabirds worldwide. Our findings show the importance of biological and ecological factors, highlighting the role of seabirds as anthropization sentinels and ARGs-pollution environmental indicators (even in a pristine biotope), and their involvement in the One Health epidemiological chain of ARGs.

Sex and hatching order modulate the association between MHC-II diversity and fitness in early-life stages of a wild seabird.

Genes of the major histocompatibility complex (MHC) play a pivotal role in parasite resistance, and their allelic diversity has been associated with fitness variations in several taxa. However, studies report inconsistencies in the direction of this association, with either positive, quadratic or no association being described. These discrepancies may arise because the fitness costs and benefits of MHC diversity differ among individuals depending on their exposure and immune responses to parasites. Here, we investigated in black-legged kittiwake (Rissa tridactyla) chicks whether associations between MHC class-II diversity and fitness vary with sex and hatching order. MHC-II diversity was positively associated with growth and tick clearance in female chicks, but not in male chicks. Our data also revealed a positive association between MHC-II diversity and survival in second-hatched female chicks (two eggs being the typical clutch size). These findings may result from condition-dependent parasite infections differentially impacting sexes in relation to hatching order. We thus suggest that it may be important to account for individual heterogeneities in traits that potentially exert selective pressures on MHC diversity in order to properly predict MHC-fitness associations.

Evidence of Pathogen-Induced Immunogenetic Selection across the Large Geographic Range of a Wild Seabird.

Over evolutionary time, pathogen challenge shapes the immune phenotype of the host to better respond to an incipient threat. The extent and direction of this selection pressure depend on the local pathogen composition, which is in turn determined by biotic and abiotic features of the environment. However, little is known about adaptation to local pathogen threats in wild animals. The Gentoo penguin (Pygoscelis papua) is a species complex that lends itself to the study of immune adaptation because of its circumpolar distribution over a large latitudinal range, with little or no admixture between different clades. In this study, we examine the diversity in a key family of innate immune genes—the Toll-like receptors (TLRs)—across the range of the Gentoo penguin. The three TLRs that we investigated present varying levels of diversity, with TLR4 and TLR5 greatly exceeding the diversity of TLR7. We present evidence of positive selection in TLR4 and TLR5, which points to pathogen-driven adaptation to the local pathogen milieu. Finally, we demonstrate that two positively selected cosegregating sites in TLR5 are sufficient to alter the responsiveness of the receptor to its bacterial ligand, flagellin. Taken together, these results suggest that Gentoo penguins have experienced distinct pathogen-driven selection pressures in different environments, which may be important given the role of the Gentoo penguin as a sentinel species in some of the world’s most rapidly changing environments.

Ecology can inform genetics: Disassortative mating contributes to MHC polymorphism in Leach's storm-petrels (Oceanodroma leucorhoa).

Studies of MHC-based mate choice in wild populations often test hypotheses on species exhibiting female choice and male-male competition, which reflects the general prevalence of females as the choosy sex in natural systems. Here, we examined mutual mate-choice patterns in a small burrow-nesting seabird, the Leach's storm-petrel (Oceanodroma leucorhoa), using the major histocompatibility complex (MHC). The life history and ecology of this species are extreme: both partners work together to fledge a single chick during the breeding season, a task that requires regularly travelling hundreds of kilometres to and from foraging grounds over a 6- to 8-week provisioning period. Using a 5-year data set unprecedented for this species (n=1078 adults and 925 chicks), we found a positive relationship between variation in the likelihood of female reproductive success and heterozygosity at Ocle-DAB2, a MHC class IIB locus. Contrary to previous reports rejecting disassortative mating as a mechanism for maintaining genetic polymorphism in this species, here we show that males make significant disassortative mate-choice decisions. Variability in female reproductive success suggests that the most common homozygous females (Ocle-DAB2*01/Ocle-DAB2*01) may be physiologically disadvantaged and, therefore, less preferred as lifelong partners for choosy males. The results from this study support the role of mate choice in maintaining high levels of MHC variability in a wild seabird species and highlight the need to incorporate a broader ecological framework and sufficient sample sizes into studies of MHC-based mating patterns in wild populations in general.

Sperm collection in Black-legged Kittiwakes and characterization of sperm velocity and morphology

BackgroundCollecting and studying live sperm is central to many important fields of biology. Yet, a simple method to collect live sperm is lacking in wild seabird species. Here, we describe a non-invasive method to collect viable sperm samples based on a simple massage technique applied to male Black-legged Kittiwakes (Rissa tridactyla).MethodsWe studied a colony breeding at Kongsfjorden, Svalbard and successfully obtained sperm samples from 32 males. With a subset of samples (n = 12 males), we compared the suitability of several extenders (0.9% NaCl, PBS, Earle’s balance salt solution, Dulbecco’s modified Eagle medium) in maintaining sperm alive long enough for analyses. With another 18 ejaculates, we conducted computer assisted sperm analyses using the CASA plugin for ImageJ. We provide details about the settings to be used for such analyses. Lastly, droplets from 20 ejaculates were smeared on glass slides and preserved with formalin to characterize sperm morphology in terms of total sperm length, sperm head length, midpiece length and flagellum length, and percentage of abnormal sperm.ResultsWith this method and under field conditions, we were able to obtain sufficient amounts of live sperm to assess traits related to sperm quality (e.g. sperm morphology, percentage of motile sperm, sperm velocity). We found that two extenders, Earle’s balanced salt solution and Dulbecco modified Eagle’s medium, yielded similarly good results. Additionally, we investigated whether specific behaviours were associated with successful sperm collection and whether sperm collection success depended on how long before laying sperm collection was attempted. Finally, we provide mean values for sperm morphology, sperm swimming ability and percentage of motile sperm, which may prove useful for future comparative analyses, and we report high levels of sperm abnormality and within-ejaculate variation in sperm morphology.ConclusionsWe discuss the high percentage of abnormal sperm and high within-ejaculate variation in sperm morphology in light of sperm competition theory and conclude that these figures are likely due to relaxed post-copulatory sexual selection, kittiwakes being strictly monogamous. Finally, we suggest that this method could be applied to other seabird species sharing similar ecology.

Reproductive effort and oxidative stress: effects of offspring sex and number on the physiological state of a long‐lived bird

Summary Individuals must trade‐off between energetically costly activities to maximize their fitness. However, the underlying physiological mechanism remains elusive. Oxidative stress, the imbalance between reactive oxygen species production and antioxidant and/or repair activities, has been suggested to underlie life‐history trade‐offs: greater investment in reproduction supposedly generating higher oxidative damage, thus reducing life span. While most studies used natural or experimental variation in offspring number to examine how reproduction affects oxidative stress, none studied the impact of offspring sex, although it could influence physiological costs and fitness, if the sexes differ in terms of energetic cost. Here, we aim at further understanding how reproduction (in terms of offspring sex, experimentally manipulated and number, not manipulated) influences oxidative stress in a wild seabird, where sons are energetically costlier than daughters. We did so by conducting a chick fostering experiment (to disentangle foster and produced sex ratio) and using four oxidative stress markers plus baseline corticosterone. First, the results suggest that individual physiological state before laying modulates upcoming reproductive effort. Individuals with higher pre‐laying baseline corticosterone and lower antioxidant activity, estimated by their superoxide dismutase activity, subsequently invested more in reproduction, estimated by the cumulative number of days spent rearing chicks. Hence, it seems that only individuals that could afford to invest heavily in reproduction did so. Then, we examined the effects of reproductive effort on individual physiological state at the end of the breeding season. Higher reproductive effort seemed to imply higher physiological costs. Oxidative stress, estimated by the ratio of oxidized over reduced glutathione, increased with more male‐biased foster sex ratio among mothers but not among fathers, whereas baseline corticosterone did so in both sexes. Similarly, lipid oxidative damage to red blood cells increased with increasing cumulative number of days spent rearing chicks. Our study provides the first evidence that brood sex ratio variation can affect oxidative balance, potentially in a sex‐specific way, although more studies are needed to understand whether the observed physiological costs could lead to fitness costs. It also highlights the need to consider sex ratio in future studies investigating the role of oxidative stress in life‐history trade‐offs. A lay summary is available for this article.

Nutritional composition of Mutton bird (Puffinus griseus) meat

Mutton birds (Puffinus griseus) are wild seabird chicks traditionally harvested by Maori but available commercially for seasonal consumption in New Zealand. Little information is available on the nutritional content of the meat from these birds. Proximate analysis and amino and fatty acid composition of Mutton bird breast meat (MBBM) were measured over two harvesting seasons, 2007 and 2008. Protein content was lower, and fat and ash contents were higher (P<0.05) in meat from birds harvested in 2008 (18.5, 13.0 and 11.7%, respectively) compared with that from 2007 (20.3, 11.8 and 10.3%, respectively). Higher lysine concentrations and lower proline, cysteine and methionine were found in MBBM compared with literature values for beef, lamb and pork. The essential amino acid content in Mutton bird (41.7 and 38.4% for 2008 and 2007, respectively) was slightly lower than those reported for common meats (42–43%). Palmitic, arachidonic, DHA, stearic, EPA, and oleic were the major fatty acids (FA) detected in MBBM and accounted for approximately 60% of the FA. The cholesterol concentration was not affected by season. Seasonal variations MBBM existed which may be of little nutritional consequence but might be a useful indicator for ecological events including changing feed availability.

Identifying the selective pressures underlying offspring sex-ratio adjustments: a case study in a wild seabird

Sex allocation theory predicts that parents should bias offspring sex according to the costs and benefits associated with producing either sex in a given context. Accurately interpreting sex-ratio biases, therefore, requires a precise identification of these selective pressures. However, such information is generally lacking. This may partly explain the inconsistency in reported sex allocation patterns, especially in vertebrates. We present data from a long-term feeding experiment in black-legged kittiwakes (Rissa tridactyla) that allowed us to increase investment capacity for some breeding pairs. Previous findings showed that these pairs then overproduced sons compared with control parents. Here, our aim was to test the underlying assumptions of the 2 appropriate sex allocation models for our context: the “cost of reproduction hypothesis” and the “Trivers–Willard hypothesis.” The former assumes a sex difference in rearing costs, whereas the latter assumes a difference in fitness returns. 1) Independent of feeding treatment, rearing sons was energetically more demanding for parents (as revealed by higher energy expenditure and higher baseline corticosterone levels) than rearing daughters, thereby corroborating the underlying assumption of the “cost of reproduction hypothesis.” 2) Evidence supporting the assumptions of the “Trivers–Willard hypothesis” was less convincing. Overall, our results suggest that drivers of parental sex allocation decisions are probably more related to offspring sex-specific energetic costs than to their future reproductive success in our study species. Assessing the adaptive value of sex-ratio biases requires precise investigation of the assumptions underlying theoretical models, particularly as long as the mechanisms involved in sex-ratio manipulation remain largely unknown.

Physiological and fitness correlates of experimentally altered hatching asynchrony magnitude in chicks of a wild seabird

Nest-bound chicks depend entirely on their parents for food, often leading to high sibling competition. Asynchronous hatching, resulting from the onset of incubation before clutch completion, facilitates the establishment of within-nest hierarchy, with younger chicks being subject to lower feeding and growth rates. Because social and nutritional stresses affect baseline stress hormone levels in birds, younger chicks are expected to have higher levels of corticosterone than their siblings. As previous studies showed that hatching asynchrony magnitude influences the course of sibling competition, it should also affect baseline corticosterone. We measured baseline corticosterone at age 5days in nestling black-legged kittiwakes (Rissa tridactyla) in 3 types of experimental broods: synchronous, asynchronous, and highly asynchronous. Sexual dimorphism takes place during chick-rearing and might also influence baseline corticosterone, we thus included chick sex in our analyses and also monitored chick growth and survival. Baseline corticosterone did not differ among A-chicks, but was higher in B-chicks from highly asynchronous broods compared with the other brood types, in line with the presumed increase in nutritional stress. In asynchronous broods, A-chicks had higher baseline corticosterone than their siblings, contrary to our expectations. We interpret that result as a cost of dominance among A-chicks. In line with previous studies, mass gain was negatively correlated with baseline corticosterone levels. We found that baseline corticosterone predicted survival in a sex-specific way. Regardless of hatching rank, males with higher baseline corticosterone suffered higher mortality, suggesting that males were more sensitive to high level of stress, independently of its cause.

Endoscopy as a novel method for assessing endoparasite burdens in free‐ranging European shags (Phalacrocorax aristotelis)

Abstract Parasites are considered to be a key driver of evolutionary processes in wild animal populations. However, assessing host‐endoparasite burdens non‐destructively is problematic. Collection of faecal samples can be difficult, and faecal egg counts may not always be a reliable indicator of infection intensity. Here we report on endoscopy as a method for assessing natural burdens of nematode parasites Contracaecum rudolphii Hartwich, 1964, in a wild seabird, the European shag (Phalacrocorax aristotelis, L.). We aimed to measure natural individual parasite burdens and repeatability of burdens over time, and to verify that treatment with ivermectin removed parasites. Endoscopy was rapid, averaging 6 min (n = 157), with no obvious adverse effects on behaviour or breeding success compared to non‐endoscoped birds. Nematode burdens in the oesophagus and proventriculus of conscious shags were counted and classified as absent, low, medium or high using a flexible gastroscope with a camera attachment that recorded video footage. Re‐assessment of worm burdens was highly accurate, with 94% of randomly selected videos (n = 50) giving identical categorical scores, and 70% of worm counts (n = 40) giving the same total or differing by only one worm. All birds were parasitised by C. rudolphii. Natural burdens were significantly higher in males and in late breeders. Individuals had highly repeatable categorical parasite scores over time with 65% of control birds sampled more than once (n = 17; mean interval between assessments= 10·8 days) showing no change in scores. However, although the rank ordering of birds based on categorical scores remained constant, more finely resolved quantification indicated a slight seasonal decline in worm counts within individuals. Treatment with ivermectin (4 mg kg−1 of bird weight) resulted in complete removal of parasites. There was some evidence of temporal declines in worm counts with lower doses of ivermectin, including a dose (0·7 mg kg−1) previously shown to impact chick survival and growth. Endoscopy has considerable potential for investigating individual variation and temporal changes in endoparasite burdens and drug efficacy. Applicability and limitations of this method for other host‐parasite systems are discussed.

Concentrations of trace elementals and organochlorines in Mutton bird ( Puffinus griseus)

The Sooty Shearwater ( Puffinus griseus, commonly known as Mutton bird) is a migratory wild seabird, annually harvested for food by certain native groups in New Zealand and Australia and in many parts of the world. The concentrations of 22 elements and several organochlorine pesticides [2,2-bis(chlorophenyl)-1,1,1-trichloroethane (DDT), its derivatives dichlorodiphenyldichloroethene (DDE) and dichlorodiphenyldichloroethane (DDD), aldrin, chlordane, dicofol, lindane, and methoxychlor] in Mutton bird were determined over two consecutive years to evaluate its safety for human consumption. Twenty bird carcasses were purchased in each of 2007 and 2008 from a local source. No significant year effect ( P>0.05) was found in the following nine trace elements: Al, As, Cd, Co, Cr, Cu, Ni, Pb and Se. The concentrations of Hg, Li and Na were higher ( P<0.05) in 2008 samples compared to 2007. The toxic trace elements (mg/kg wet weight) in all the samples were below the maximum residual level (MRL). The concentration of Fe, Ca and Se in Mutton bird was higher than that in domestic land animal meats reported in literature. The residual organochlorine concentrations were all below the recommended MRL. Thus Mutton bird meat is high in essential nutrient elements and of low toxicological risk. Due to active use of agrochemical in New Zealand, a monitoring program for contaminants in Mutton birds is recommended.

Differences in the stable isotope signatures of seabird egg membrane and albumen – implications for non‐invasive studies

In many bird species, egg membranes can be obtained non-invasively after the chicks have hatched, and stable isotope analysis of egg membranes can be used to study the diet and foraging distribution of these birds during egg formation. It has been suggested that the enrichment factors of albumen and egg membranes differ for 13C, but are similar for 15N. In this study, we compared carbon and nitrogen stable isotopes of the membranes and albumen of individual eggs of three wild seabird species, the Southern Rockhopper penguin Eudyptes chrysocome, the Imperial shag Phalacrocorax atriceps albiventer, and the Thin-billed prion Pachyptila belcheri. We also included chicken eggs for comparison. Egg membranes were generally enriched in 13C, compared with albumen. The difference varied between species, with 2.1 per thousand in Rockhopper penguins, 1.6 per thousand in Imperial shags, but only 0.5 per thousand in Thin-billed prions and 0.4 per thousand in chicken eggs. Egg membranes were slightly enriched in 15N in Imperial shags (0.9 per thousand) and chickens (0.5 per thousand), compared with albumen, while there was no difference for Thin-billed prions and Rockhopper penguins. The isotopic values of carbon and nitrogen were correlated between albumen and egg membranes of individual eggs, suggesting that egg membranes can be used reliably to investigate trophic differences between individuals, seasons or colonies. Species-specific mathematical corrections could be used to compare results across studies that use different egg components.

Kinetics, dose‐response, excretion, and toxicity of methylmercury in free‐living Cory's shearwater chicks

Methylmercury (MHg) kinetics, dose-response, excretion, and toxicity were experimentally evaluated and compared between small (one to two weeks old) and large (six to seven weeks old), free-living Cory's shearwater chicks. The half-time for the terminal elimination phase of MHg in blood (5.7 d) and the average percentage of ingested MHg deposited in the blood volume (12%) were independent of the age at exposure. Therefore, these data were employed to derive a relationship between steady-state blood concentrations and dietary intake of MHg in bird chicks. Plumage:blood ratios were independent of dose and could be used as partition coefficients. Dose-response relationships in plumage and blood were linear over the wide range of exposures employed. Blood dose-responses of MHg in small and large chicks were similar. Excretion percentages into the final plumage varied between 42 and 60% of intake. The body condition of experimental chicks did not indicate sublethal toxicity of the doses administered; hence, the exposure levels provide maximum avian no-observed-adverse-effect levels for external symptoms in wild seabird chicks.

The endocrine control of reproduction and molt in male and female emperor ( Aptenodytes forsteri) and adelie ( Pygoscelis adeliae) penguins : II. Annual changes in plasma levels of thyroxine and triiodothyronine

Changes in plasma thyroxine (T 4) and triiodothyronine (T 3) levels were studied during a breeding season and in more detail during the postbreeding molt in male and female emperor ( Aptenodytes forsteri) and adelie ( Pygoscelis adeliae) penguins under natural conditions in the Antarctic. During the 4-month natural fast that accompanies courtship and incubation in male emperors, plasma T 4 and T 3 levels were maintained around 11 and 0.6 ng/ml, respectively. In courting, fasting female emperors plasma T 4 levels were maintained around 10 ng/ml for more than 1 month; plasma T 3 levels were around 0.8 ng/ml but were markedly depressed (0.1 ng/ml) at the time of copulation although they increased again (2.2 ng/ml) at oviposition. During the 5-month period of chick rearing, plasma T 3 (males and females) and T 4 (females) were maintained at the same levels as during courtship and incubation, but plasma T 4 levels in male emperors were slightly lower (7 ng/ml). Similar plasma T 4 and T 3 levels were observed in breeding adelie penguins. These results do not provide any convincing evidence for thyroid-gonadal interrelations in breeding penguins, but demonstrate their capacity to maintain plasma thyroid hormone levels during very prolonged natural fasts. During the heavy postnuptial molt when the birds were fasting, in both species and sexes, marked but separate peaks in plasma T 4 and T 3 levels occurred concurrently with the initial growth of the new feathers, and with the subsequent shedding of the old plumage, respectively. Peak plasma T 4 levels were observed at the time of the emergence of the new feathers out of the skin, and peak plasma T 3 levels were roughly concurrent with the maximum daily body weight loss. This is the first strong evidence that increases in plasma T 4 and T 3 levels are correlated with different stages of molt in a wild seabird. Increased plasma T 4 but not T 3 levels at the time of feather papilla eruption suggest that T 4 is concerned with feather growth, but is not exclusive of a role of T 3. Increased plasma T 3 but not T 4 levels during the reduction in thermal insulation in molting penguins suggest that this hormone rather than T 4 might be active in energy metabolism in penguins.