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At least 217 records · Page 12Linked to original sources
USGS2025

Avian navigation: Comparing the olfactory navigational “map” and the infrasound direction-finding hypotheses to aeronautics

Animal navigation has long been a fascinating but bewildering subject. Humans and animals might well share similar navigational strategies because they developed within the same physical environments. A “map-and-compass” model has been proposed to explain the two-step avian navigational process, but the “map” step has remained elusive. Although scalar values from bicoordinate geomagnetic or atmospheric olfactory gradients have been considered foundational to the avian map, neither has proved convincing engendering decades of controversy. The olfactory map, and an alternative infrasound direction-finding (IDF) hypothesis, are discussed in this review. The olfactory map hypothesis currently requires extensive stable gradients of trace-odor ratios, but such gradients are highly unlikely within a turbulent and rapidly mixed lower atmosphere. The IDF hypothesis, on the other hand, postulates a two-step navigational model analogous to the maritime and aeronautical radio direction-finding technique. This review was also written to encourage further investigation, and direct testing, of the acoustic navigational process. The IDF hypothesis, at present, appears the better explanation of observed avian navigational behavior and accuracy within the atmosphere’s physical environment.

Journal of Comparative Physiology A↗
USGS1991

Male sex steroids and hormonal control of male courtship behavior in the yellow-bellied slider turtle, Trachemys scripta

Survey of androgens and estrogens in serum, liver and testes of male yellow-bellied slider turtles, Trachemys (= Pseudemys ) scripta , a species exhibiting dissociated gametogenesis age-dependent melanism, revealed the presence of numerous androgen precursors, androgens, androgen metabolites, and estrogens in quantities varying with season, tissue, and male coloration. The most commonly found and abundant androgens in all males were dehydroepiandrosterone (DHEA) and androstenedione, which were present at significantly higher levels in testes than in serum or liver. Epitestosterone was found in the serum and liver of only melanistic males; testosterone was only rarely recovered. Behavioral testing of castrated male turtles implanted with various androgens, as well as intact and sham-operated controls, revealed that melanistic males courted more frequently than nonmelanistic males, and that exogenous testosterone was most effective in inducing courtship behavior in castrated males.

Comparative Biochemistry and Physiology, Part A: M↗
USGS2010

Oviduct modifications in foam-nesting frogs, with emphasis on the genus Leptodactylus (Amphibia, Leptodactylidae)

Various species of frogs produce foam nests that hold their eggs during development. We examined the external morphology and histology of structures associated with foam nest production in frogs of the genus Leptodactylus and a few other taxa. We found that the posterior convolutions of the oviducts in all mature female foam-nesting frogs that we examined were enlarged and compressed into globular structures. This organ-like portion of the oviduct has been called a “foam gland” and these structures almost certainly produce the secretion that is beaten by rhythmic limb movements into foam that forms the nest. However, the label “foam gland” is a misnomer because the structures are simply enlarged and tightly folded regions of the pars convoluta of the oviduct, rather than a separate structure; we suggest the name pars convoluta dilata (PCD) for this feature. Although all the foam-nesters we examined had a pars convoluta dilata , its size and shape showed considerable interspecific variation. Some of this variation likely reflects differences in the breeding behaviors among species and in the size, type, and placement of their foam nests. Other variation, particularly in size, may be associated with the physiological periodicity and reproductive state of the female, her age, and/or the number of times she has laid eggs.

South American Journal of Herpetology↗
USGS2024

Using global remote camera data of a solitary species complex to evaluate the drivers of group formation

The social system of animals involves a complex interplay between physiology, natural history, and the environment. Long relied upon discrete categorizations of “social” and “solitary” inhibit our capacity to understand species and their interactions with the world around them. Here, we use a globally distributed camera trapping dataset to test the drivers of aggregating into groups in a species complex (martens and relatives, family Mustelidae , Order Carnivora ) assumed to be obligately solitary. We use a simple quantification, the probability of being detected in a group, that was applied across our globally derived camera trap dataset. Using a series of binomial generalized mixed-effects models applied to a dataset of 16,483 independent detections across 17 countries on four continents we test explicit hypotheses about potential drivers of group formation. We observe a wide range of probabilities of being detected in groups within the solitary model system, with the probability of aggregating in groups varying by more than an order of magnitude. We demonstrate that a species’ context-dependent proclivity toward aggregating in groups is underpinned by a range of resource-related factors, primarily the distribution of resources, with increasing patchiness of resources facilitating group formation, as well as interactions between environmental conditions (resource constancy/winter severity) and physiology (energy storage capabilities). The wide variation in propensities to aggregate with conspecifics observed here highlights how continued failure to recognize complexities in the social behaviors of apparently solitary species limits our understanding not only of the individual species but also the causes and consequences of group formation.

PNAS↗
USGS2017

Predictive framework for estimating exposure of birds to pharmaceuticals

We present and evaluate a framework for estimating concentrations of pharmaceuticals over time in wildlife feeding at wastewater treatment plants (WWTPs). The framework is composed of a series of predictive steps involving the estimation of pharmaceutical concentration in wastewater, accumulation into wildlife food items, and uptake by wildlife with subsequent distribution into, and elimination from, tissues. Because many pharmacokinetic parameters for wildlife are unavailable for the majority of drugs in use, a read-across approach was employed using either rodent or human data on absorption, distribution, metabolism, and excretion. Comparison of the different steps in the framework against experimental data for the scenario where birds are feeding on a WWTP contaminated with fluoxetine showed that estimated concentrations in wastewater treatment works were lower than measured concentrations; concentrations in food could be reasonably estimated if experimental bioaccumulation data are available; and read-across from rodent data worked better than human to bird read-across. The framework provides adequate predictions of plasma concentrations and of elimination behavior in birds but yields poor predictions of distribution in tissues. The approach holds promise, but it is important that we improve our understanding of the physiological similarities and differences between wild birds and domesticated laboratory mammals used in pharmaceutical efficacy/safety trials, so that the wealth of data available can be applied more effectively in ecological risk assessments.

Environmental Toxicology and Chemistry↗
USGS2014

Physiological condition of juvenile wading birds in relation to multiple landscape stressors in the Florida Everglades: effects of hydrology, prey availability, and mercury bioaccumulation

The physiological condition of juvenile birds can be influenced by multiple ecological stressors, and few studies have concurrently considered the effects of environmental contaminants in combination with ecological attributes that can influence foraging conditions and prey availability. Using three temporally distinct indices of physiological condition, we compared the physiological response of nestling great egrets ( Ardea alba ) and white ibises ( Eudocimus albus ) to changing prey availability, hydrology (water depth, recession rate), and mercury exposure in the Florida Everglades. We found that the physiological response of chicks varied between species and among environmental variables. Chick body condition (short-term index) and fecal corticosterone levels (medium-term) were influenced by wetland water depth, prey availability, region, and age, but not by mercury contamination. However, mercury exposure did influence heat shock protein 70 (HSP70) in egret chicks, indicating a longer-term physiological response to contamination. Our results indicate that the physiological condition of egret and ibis chicks were influenced by several environmental stressors, and the time frame of the effect may depend on the specialized foraging behavior of the adults provisioning the chicks.

Florida↗
USGS2007

Reproductive physiology of Missouri River gravid pallid sturgeon and shovelnose sturgeon during the 2005 and 2006 spawning seasons: Chapter C in Factors affecting the reproduction, recruitment, habitat, and population dynamics of pallid sturgeon and shovelnose sturgeon in the Missouri River

In a natural, unaltered river, the location and timing of sturgeon spawning will be dictated by the prevailing environmental conditions to which the sturgeon have adapted. A goal of the Comprehensive Sturgeon Research Program (CSRP; see chap. A) at the U.S. Geological Survey Columbia Environmental Research Center is to identify where, when, and under what conditions shovelnose sturgeon ( Scaphirhynchus platorynchus ) and pallid sturgeon ( S. albus ) spawn in the altered Missouri River so that those conditions necessary for spawning success can be defined. One approach to achieving this goal is to exploit what is known about fish reproductive physiology to develop and apply a suite of diagnostic indicators of readiness to spawn. In 2005 and 2006, gravid shovelnose sturgeon and a limited number of pallid sturgeon were fitted with transmitters and tracked on their spawning migration. A suite of physiological indicators of reproductive state such as reproductive hormones and oocyte development were measured. These same measurements were made on tissues collected from additional fish, presumably migrating to spawn, that were not tagged or tracked. The data presented here indicating the sturgeons’ readiness to spawn are to be evaluated together with their behavior and the environmental conditions. The U.S. Army Corps of Engineers (ACOE) Sturgeon Response to Flow Modification (SRFM; see chap. A) study, initiated in 2006, provides additional opportunities to experimentally evaluate the sturgeon reproductive response indicators relative to changes in flow. In this chapter, we report progress made on identifying and developing the physiological indicators and summarize 2 years’ worth of indicator data collected thus far.

Missouri River, Yellowstone River↗
USGS2011

Effects of supplemental feeding and aggregation on fecal glucocorticoid metabolite concentrations in elk

Habitat modifications and supplemental feeding artificially aggregate some wildlife populations, with potential impacts upon contact and parasite transmission rates. Less well recognized, however, is how increased aggregation may affect wildlife physiology. Crowding has been shown to induce stress responses, and increased glucocorticoid (GC) concentrations can reduce immune function and increase disease susceptibility. We investigated the effects of supplemental feeding and the aggregation that it induces on behavior and fecal glucocorticoid metabolite concentrations (fGCM) in elk (Cervus elaphus) using observational and experimental approaches. We first compared fGCM levels of elk on supplemental feedgrounds to neighboring elk populations wintering in native habitats using data from 2003 to 2008. We then experimentally manipulated the distribution of supplemental food on feedgrounds to investigate whether more widely distributed food would result in lower rates of aggression and stress hormone levels. Contrary to some expectations that fed elk may be less stressed than unfed elk during the winter, we found that elk on feedgrounds had fecal GC levels at least 31% higher than non-feedground populations. Within feedgrounds, fGCM levels were strongly correlated with local measures of elk density (r 2 = 0.81). Dispersing feed more broadly, however, did not have a detectable effect on fGCM levels or aggression rates. Our results suggest that increases in aggregation associated with winter feedgrounds affects elk physiology, and the resulting increases in fGCM levels are not likely to be mitigated by management efforts that distribute the feed more widely. Additional research is needed to assess whether these increases in fGCMs directly alter parasite transmission and disease dynamics.

Journal of Wildlife Management↗
USGS1981

Spatial variation in transferrin allele frequencies among herds of feral donkeys in Death Valley National Monument, California

Serum proteins were studied to clarify interrelationships of seemingly disjunct herds of feral donkeys ( Equus asinus ) in the mountains of Death Valley National Monument, California. Sera of 162 donkeys from five localities in the Panamint Mountains were examined by starch-gel electrophoresis to assess polymorphic variation in transferrins. Four homozygous and six heterozygous transferrin phenotypes controlled by four codominant, autosomal alleles were identified with Fe 59 autoradiography. Significant interlocality heterogeneity in genotype distribution and allele frequency distribution among herds was demonstrated. The maximum distance between adjacent herds was 52 km and the minimum distance was 14 km. There are no major physical barriers to movements between herds; furthermore, donkeys are highly mobile animals capable of extensive travel. Behavioral isolation of adjacent herds occurs from May through July, during the peak of reproduction. This isolation is reinforced by fidelity of individuals to their respective home ranges, and to physiological dependence on permanent sources of water. Adjacent herds may overlap during winter when breeding and dependence on water sources are reduced.

Journal of Mammalogy↗
USGS2022

Using piecewise regression to identify biological phenomena in biotelemetry datasets

1. Technological advances in the field of animal tracking have greatly expanded the potential to remotely monitor animals, opening the door to exploring how animals shift their behavior over time or respond to external stimuli. A wide variety of animal-borne sensors can provide information on an animal’s location, movement characteristics, external environmental conditions, and internal physiological status. 2. Here, we demonstrate how piecewise regression can be used to identify the presence and timing of potential shifts in a variety of biological responses using GPS telemetry and other biologging data streams. Different biological latent states can be inferred by partitioning a time-series into multiple segments based on changes in modeled responses (e.g., their mean, variance, trend, degree of autocorrelation) and specifying a unique model structure for each interval. 3. We provide six example applications highlighting a variety of taxonomic species, data streams, timescales and biological phenomena. These examples include a short-term behavioural response (flee and return) by a trumpeter swan Cygnus buccinator following a GPS collar deployment; remote identification of parturition based on movements by a pregnant moose Alces alces ; a physiological response (spike in heart-rate) in a black bear Ursus americanus to a stressful stimulus(presence of a drone); a mortality event of a trumpeter swan signalled by changes in collar temperature and overall dynamic body acceleration; an unsupervised method for identifying the onset, return, duration and staging use of sandhill crane Antigone canadensis migration; and estimation of the transition between incubation and brood-rearing (i.e. hatching) for a breeding trumpeter swan. 4. We implement analyses using the MCP package in R, which provides functionality for specifying and fitting a wide variety of user-defined model structures in a Bayesian framework and methods for assessing and comparing models using information criteria and cross-validation measures.

Journal of Animal Ecology↗
USGS2022

Pathways of productivity and influences on top consumers in forested streams

Forested stream ecosystems involve complex physical and biotic pathways that can influence fish in numerous ways. Consequently, the responses of fish communities to disturbance can be difficult to understand. In this study, we employed a food web model that links biotic (e.g., physiology, predator–prey interactions) and abiotic (e.g., temperature, sunlight) attributes to address fish responses to changes in stream-riparian ecosystems. We modeled responses to food web dynamics in four streams, using scenarios that included responses to riparian disturbance, climate change, and shifts in top consumers. The two consumers we focused on were coastal cutthroat trout ( Oncorhynchus clarkii clarkii ) and sculpin ( Cottus spp., collectively treated as a functional group) . We found the responses to environmental changes varied by fish species and among streams, and that responses were not independent due to exploitative interspecific competition. Simulations based on long-term data indicated that coastal cutthroat trout were responsive to changes in allochthonous resources including terrestrial detritus and invertebrates, whereas sculpin were more responsive to changes to autochthonous resources that included, periphyton and aquatic invertebrates. These results may be, in part, a consequence of species-specific foraging behavior. Trout have a higher propensity to drift feed and therefore receive a substantial subsidy from terrestrial invertebrates, whereas sculpin feed mostly on aquatic insects on the streambed. Simulations of changes in summer temperature and stream discharge suggest decreased biomass of both fish species because of physiological constraints on invertebrate prey which reduce fish foraging opportunities. Exploitative competition also may be important in fish responses: when one fish taxon was removed, the other showed increased biomass. Although the pattern of simulation results was consistent across the four streams, the magnitude of change varied among streams. Streams with food webs fueled by multiple energy sources may be more resilient to changes to riparian forests and climate. Through application of a systems model, we gained insights into pathways of productivity for fish in forested stream ecosystems that provide understanding of processes that influence fish and streams, as well as implications for management of both.

Forest Ecology and Management↗
USGS2007

Interactions across spatial scales among forest dieback, fire, and erosion in northern New Mexico landscapes

Ecosystem patterns and disturbance processes at one spatial scale often interact with processes at another scale, and the result of such cross-scale interactions can be nonlinear dynamics with thresholds. Examples of cross-scale pattern-process relationships and interactions among forest dieback, fire, and erosion are illustrated from northern New Mexico (USA) landscapes, where long-term studies have recently documented all of these disturbance processes. For example, environmental stress, operating on individual trees, can cause tree death that is amplified by insect mortality agents to propagate to patch and then landscape or even regional-scale forest dieback. Severe drought and unusual warmth in the southwestern USA since the late 1990s apparently exceeded species-specific physiological thresholds for multiple tree species, resulting in substantial vegetation mortality across millions of hectares of woodlands and forests in recent years. Predictions of forest dieback across spatial scales are constrained by uncertainties associated with: limited knowledge of species-specific physiological thresholds; individual and site-specific variation in these mortality thresholds; and positive feedback loops between rapidly-responding insect herbivore populations and their stressed plant hosts, sometimes resulting in nonlinear “pest” outbreak dynamics. Fire behavior also exhibits nonlinearities across spatial scales, illustrated by changes in historic fire regimes where patch-scale grazing disturbance led to regional-scale collapse of surface fire activity and subsequent recent increases in the scale of extreme fire events in New Mexico. Vegetation dieback interacts with fire activity by modifying fuel amounts and configurations at multiple spatial scales. Runoff and erosion processes are also subject to scale-dependent threshold behaviors, exemplified by ecohydrological work in semiarid New Mexico watersheds showing how declines in ground surface cover lead to non-linear increases in bare patch connectivity and thereby accelerated runoff and erosion at hillslope and watershed scales. Vegetation dieback, grazing, and fire can change land surface properties and cross-scale hydrologic connectivities, directly altering ecohydrological patterns of runoff and erosion. The interactions among disturbance processes across spatial scales can be key drivers in ecosystem dynamics, as illustrated by these studies of recent landscape changes in northern New Mexico. To better anticipate and mitigate accelerating human impacts to the planetary ecosystem at all spatial scales, improvements are needed in our conceptual and quantitative understanding of cross-scale interactions among disturbance processes.

New Mexico↗
USGS2012

Does translocation influence physiological stress in the desert tortoise?

Wildlife translocation is increasingly used to mitigate disturbances to animals or habitat due to human activities, yet little is known about the extent to which translocating animals causes stress. To understand the relationship between physiological stress and translocation, we conducted a multiyear study (2007–2009) using a population of desert tortoises (Gopherus agassizii) near Fort Irwin, California. Blood samples were collected from adult tortoises in three treatment groups (resident, translocated and control) for 1 year prior to and 2 years after translocation. Samples were analyzed by radioimmunoassay for plasma total corticosterone (CORT), a glucocorticoid hormone commonly associated with stress responses in reptiles. CORT values were analyzed in relation to potential covariates (animal sex, date, behavior, treatment, handling time, air temperature, home-range size, precipitation and annual plant production) among seasons and years. CORT values in males were higher than in females, and values for both varied monthly throughout the activity season and among years. Year and sex were strong predictors of CORT, and translocation explained little in terms of CORT. Based on these results, we conclude that translocation does not elicit a physiological stress response in desert tortoises.

California↗
USGS2011

Nest predation and circulating corticosterone levels within and among species

Variation in the risk of predation to offspring can influence the expression of reproductive strategies both within and among species. Appropriate expression of reproductive strategies in environments that differ in predation risk can have clear advantages for fitness. Although adult-predation risk appears to influence glucocorticosteroid levels, leading to changes in behavioral and life-history strategies, the influence of offspring-predation risk on adult glucocorticosteroid levels remains unclear. We compared total baseline corticosterone concentrations in Gray-headed Juncos (Junco hyemalis dorsalis) nesting on plots with and without experimentally reduced risk of nest predation. Despite differences in risk between treatments, we failed to find differences in total baseline corticosterone concentrations. When we examined corticosterone concentrations across a suite of sympatric species, however, higher risk of nest predation correlated with higher total baseline corticosterone levels. As found previously, total baseline corticosterone was negatively correlated with body condition and positively correlated with date of sampling. However, we also found that corticosterone levels increased seasonally, independent of stage of breeding. Nest predation can alter the expression of birds' reproductive strategies, but our findings suggest that total baseline corticosterone is not the physiological mechanism regulating these responses.

The Condor↗
USGS2018

Range expansion in unfavorable environments through behavioral responses to microclimatic conditions: Moose (Alces americanus) as the model

Wildlife populations occurring at the edge of their range boundaries are thought to be the most sensitive to climate change due to temperatures being at or near the limit of a species’ thermal envelope. Moose ( Alces americanus ) are a cold adapted species that are showing population declines in some portions of the southern edge of their range. However, other moose populations are actively expanding southward into thermally stressful areas. The direct effects of temperature on moose have not yet been studied in these southwardly expanding populations and may offer insights into how moose are successfully establishing in areas at the edge of their thermal envelope. We used ambient temperature and GPScollar data from moose to quantify the direct effect of temperature on moose habitat use in Massachusetts, USA, which is one of these southwardly expanding populations. The mean daily temperature in our study area exceeded the reported physiological tolerances of moose in over 90% of daytime and 75% of nighttime locations in summer and in over 80% of daytime and 67% of nighttime locations in winter. Across seasons and times of day, moose preferred regenerating forest, but as ambient air temperatures increased, selection for regenerating forest declined and selection for forested wetlands and coniferous forestincreased. This response indicates moose are altering their behavior to utilize thermal shelters when temperatures are high. We observed higher temperatures and stronger behavioral responses than other studies at the southern edge of moose range. We found habitat for moose in Massachusetts is climatically marginal and loss of habitat, increase in parasites, and further climatic warming may cause population declines in the future.

Mammalian Biology↗
USGS2025

Electric field-induced detachment and vibration analysis for Sea Lamprey

Objective: Sea lamprey Petromyzon marinus , a known ecological threat to native fish populations in the Great Lakes, use their oral suction disc to navigate challenging environments when moving upstream to spawn. This study investigated the physiological response of adult sea lamprey to detach under pulsed direct current electric fields. Methods: Adult sea lampreys in an attaching position were exposed to pulsed direct current electric fields at four different field strengths (0.7, 1.1, 1.3, and 1.9 V/cm). Behavioral responses, including detachment and vibration, were observed and analyzed. Fast Fourier Transform analysis was applied to vibration data to quantify the frequency of vibration exhibited by non-detached sea lamprey. Statistical correlations between detachment rates and vibration responses to sea lamprey sex, weight, and length were evaluated to determine influencing factors. Results: The highest detachment rate (91%) was observed at 1.1 V/cm, with the detachment rate above 70% for other field strengths. Fast Fourier Transform analysis revealed that the vibration frequencies closely matched the signal while stronger fields elicited a more pronounced vibration amplitude without significantly increasing detachment. Non-detached sea lampreys exhibited “twitching” behavior synchronized with the electric field frequency. Sex, weight, and length had minimal influence on detachment rates and vibration responses. Conclusion: This study provided insights into the behavioral responses of sea lamprey under electric fields, highlighting the potential for optimizing electric deterrents for selective control. While not all sea lampreys detach during electroshocking, understanding their behavior can be crucial in maximizing detachment rates and contributing to improved management strategies for this invasive species.

Transactions of the American Fisheries Society↗
USGS2020

Surficial geochemistry and bioaccessibility of tellurium in semi-arid mine tailings

Tellurium (Te) is a critical element due to its use in solar technology. However, some forms are highly toxic. Few studies have examined Te behavior in the surficial environment, thus little is known about its potential human and environmental health impacts. This study characterizes two physicochemically distinct Te-enriched mine tailings piles (big and flat tailings) deposited by historic gold (Au) mining in the semi-arid Delamar mining district, Nevada. The big tailings are characterized by smaller particle size and higher concentrations of potentially toxic elements (up to 290 mg Te kg-1), which are enriched at the tailings surface. In contrast, the flat tailings have larger particle size and properties that are relatively invariant with depth. Based on the sulfate to sulfide ratio, the tailings were determined to be sulfate dominated suggesting a high degree of weathering, although the flat tailings did contain significant amounts of sulfides (~40%). Tellurium x-ray absorption spectroscopy of the big tailings indicates that tellurate, the less toxic Te species, is the principal form of Te. Electron microscopy indicates that most of the Te present at the site is associated with iron (oxy)hydroxides, sometimes with other potentially toxic elements, especially lead and antimony. Physiologically-based extraction tests indicate that substantially more Te is solubilized in synthetic stomach fluids than in lung fluids, with gastric bioaccessibility ranging from 13-31% of total Te. This points to low to medium bioaccessibility, which is common for iron (oxy)hydroxide associated elements. Together, these results represent a preliminary assessment of Te surficial behavior in a semi-arid environment and indicate that Te in these tailings represent a moderate health concern.

Environmental Chemistry↗
USGS2005

The adrenocortical response of tufted puffin chicks to nutritional deficits

In several seabirds, nutritional state of a nest-bound chick is negatively correlated with the activity of its hypothalamus-pituitary-adrenal (HPA) axis. Increased corticosterone (cort) secretion has been shown to facilitate changes in behavior that allow hungry chicks to obtain more food from parents. However, if parents are not willing/able to buffer their young from temporary food shortages, increased cort secretion could be detrimental to undernourished chicks. In a system where parents are insensitive to chick demands, low benefits and high costs of activation of the HPA-axis in hungry chicks should lead to a disassociation of the nutritional state of the young and the activity of its HPA-axis. We tested this novel hypothesis for the tufted puffin (Fratercula cirrhata), a seabird with intermittent provisioning of a nest-bound semi-precocial chick. We examined the HPA-axis activity of captive chicks exposed to the following: (1) a short-term (24 h) food deprivation; and (2) an array of prolonged (3 weeks) restrictions in feeding regimens. We found that in response to a short-term food deprivation chicks decreased baseline levels of cort and thyroid hormones. In response to prolonged restrictions, food-limited chicks exhibited signs of nutritional deficit: they had lower body mass, endogenous lipid reserves, and thyroid hormone titers compared to chicks fed ad libitum. However, baseline and maximum acute stress-induced levels of cort were also lower in food-restricted chicks compared to those of chicks fed ad libitum. These results support a major prediction of the study hypothesis that puffin chicks suppress HPA-axis activity in response to short- and long-term nutritional deficits. This physiological adaptation may allow a chick to extend its development in the nest, while eluding detrimental effects of chronic cort elevation.

Hormones and Behavior↗