Open Access Published by De Gruyter Open Access

Volume 6 Issue 1

January 2019

Issue of Animal Migration

Contents
Journal Overview

Open Access December 2, 2019

A themed collection of research articles focused on stress physiology of bird migration

Andrew K. Davis, Emily Cornelius Ruhs

Page range: 1-3

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Open Access December 2, 2019

Migratory Species Show Distinct Patterns in Corticosterone Levels during Spring and Autumn Migrations

Arseny Tsvey, Julia Loshchagina, Sergey Naidenko

Page range: 4-18

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Abstract

Twice a year billions of birds migrate between breeding and wintering grounds. To facilitate migrations, birds develop migratory disposition, a complex suite of behavioral and physiological adjustments. Glucocorticoid hormone corticosterone is involved in the regulation of migratory behavior and physiology, however no consensus on its exact role in controlling avian migration exists. Using a large dataset on seven songbird species (long- and short-distance migrants) obtained during eleven consecutive migratory seasons on the Courish Spit of the Baltic Sea, we showed the general tendency of similar baseline corticosterone concentrations during both migrations, although stress-induced levels were generally much higher during spring. No difference between long- and short-distance migrants was found in either baseline or stress-induced levels, while there was substantial between-species variation, especially in baseline concentrations. The distinct patterns of corticosterone secretion during seasonal migrations even in ecologically similar species indicate that it is likely to be a species-specific trait. Thus, our study corroborates the inconsistency found in earlier studies and demonstrates how scientific understanding of the role of corticosterone during migration is still evolving. Rather low baseline corticosterone concentrations observed in this study emphasize that birds in both migratory seasons were not in a “stressed” state before capture.

Open Access December 2, 2019

Migratory state is not associated with differences in neural glucocorticoid or mineralocorticoid receptor expression in pine siskins

Heather E. Watts, Jeffrey L. Rittenhouse, Kendra B. Sewall, J. Michael Bowers

Page range: 19-27

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Abstract

Although the endocrine system likely plays an important role in orchestrating the transition to a migratory state, the specific mechanisms by which this occurs remain poorly understood. Changes in glucocorticoid signaling are one proposed mechanism that may be important in migratory transitions. Although previous work has focused on the role of changes in circulating glucocorticoids, another potential mechanism is changes in the expression of its cognate receptors. Here, we test this hypothesis by comparing mRNA expression of the genes for the mineralocorticoid receptor ( MR ) and glucocorticoid receptor ( GR ) in two brain regions implicated in the regulation of migratory behavior (the hippocampus and hypothalamus) in pine siskins ( Spinus pinus ) sampled before or after the transition to a spring nomadic migratory state. Compared to pre-migratory birds, migratory birds had body conditions more indicative of physiological preparations for migration (e.g., larger body mass), and greater levels of nocturnal migratory restlessness. However, we found no differences between pre-migratory and migratory birds in the expression of GR or MR mRNA in either the hippocampus or hypothalamus. Thus, differences in expression of receptors for glucocorticoids do not appear to underly the observed differences in physiology and behavior across a migratory transition. Taken together with previous results showing no change in circulating corticosterone levels during this transition, our findings provide no evidence for a role of glucocorticoid signaling in the spring migratory transition of this species.

Open Access December 2, 2019

Leukocyte profiles vary with breeding latitude and infection status in a seasonally sympatric songbird

Daniel J. Becker, Katherine M. Talbott, Tara M. Smiley, Kerry L. Clark, Peter E. Sauer, Ellen D. Ketterson

Page range: 28-40

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Abstract

Billions of animals migrate annually in pursuit of food, safety, and reproduction. Long-distance migration can be energetically expensive, which can force tradeoffs with investment in other physiological systems (e.g., suppressing immunity). Understanding the physiological impacts of migration is important to predict when and where such animals may be vulnerable to parasites and how changes to migration might affect infectious disease risks. To isolate relationships between migration and physiology from energetic tradeoffs and hormonal shifts associated with spring reproduction, we assessed differences in leukocyte profiles between seasonally sympatric resident and recently arrived fall migrant dark-eyed juncos ( Junco hyemalis ) in the Appalachian Mountains. When examining heterophil:lymphocyte (HL) ratios, which can elevate for long durations after even mild stressors, we found weak associations with migratory strategy (resident or migrant subspecies). In contrast, feather δ 2 H values showed that HL ratios were highest for juncos breeding at more northern latitudes, and this relationship was strongest for birds that arrived at the overwintering site infected with haemosporidian parasites ( Plasmodium and Haemoproteus spp.). These patterns were more pronounced and better indicated hematological responses to stressors when using multivariate analyses. Our findings suggest that short- and long-distance migration may be more energetically costly in the presence of infection and highlight how approximating breeding latitude and using multivariate analyses can help understand host physiology.

Open Access December 2, 2019

Haemosporidian parasites and leukocyte profiles of pre-migratory rosy starlings (Pastor roseus) brought into captivity

Dimitar Dimitrov, Martin P. Marinov, Aneliya Bobeva, Mihaela Ilieva, Kiril Bedev, Teodor Atanasov, Pavel Zehtindjiev

Page range: 41-48

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Abstract

Immune response to pathogens such as avian malaria ( Plasmodium spp.) and related haemosporidian parasites ( Haemoproteus spp. and Leucocytozoon spp.) can lead to increases in energy demands of birds. Migrations are energetically costly for birds and require resources that could be otherwise invested in immune defence against pathogens. Here, we examined the prevalence and intensity of haemosporidian parasites (Apicomplexa, Haemosporida) in rosy starlings ( Pastor roseus ), an irruptive migrant on the Balkans, during their pre-migratory period. We further evaluated if these infections affected the stress levels of birds brought into overnight captivity, using leukocyte profiles (ratios of heterophils to lymphocytes, or H/L ratios). Haemosporidian parasites were detected based on microscopic examination, PCR and sequencing. We found high prevalence of haemosporidian parasites (83.9%) in rosy starlings (n=31), with predominant infections of Haemoproteus pastoris (cytochrome b lineage LAMPUR01) (80.1%). All birds had high heterophil/lymphocyte ratios (mean = 3.86), indicating the transition to captivity was stressful. However, there was no added stress from blood parasite infection during captivity, since infected birds did not have significantly higher heterophil/lymphocyte ratios than uninfected birds, despite all birds facing the same stress conditions. There was a negative correlation between intensity of H. pastoris and monocyte proportions, which may indicate an association with infection, or an artefact of the stress-induced shift in leukocyte profile following captivity. Our findings suggest that blood parasites have minimal additional impact on rosy starlings during an acute stress scenario (overnight captivity), arguing that they carry little cost to the energetically challenging migratory flight.

Open Access December 2, 2019

Urban residency and leukocyte profiles in a traditionally migratory songbird

Daniel J. Becker, Elizabeth M. Schultz, Jonathan W. Atwell, Ellen D. Ketterson

Page range: 49-59

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Abstract

Many animals are shifting migrations in response to human activities. In particular, human-induced changes to climate and habitat (e.g., urbanization) likely facilitate animals becoming year-round residents. Because migration can be energetically expensive, shifts to sedentary behavior could minimize energetic demands incurred and any immunosuppressive effects. Residency in urban habitats could also provide abundant resources and allow sedentary animals to invest more in immunity. However, urban habitats could also expose sedentary animals to novel stressors that counter such benefits. To examine how recent shifts to residency affects physiology in ways that may shape infectious disease dynamics, we analyzed leukocyte profiles of two dark-eyed junco ( Junco hyemalis ) populations from southern California: the Laguna Mountain population, in which birds breed in high-elevation forests and migrate altitudinally, and the urban University of California San Diego population, which was likely established by overwintering migrants in the 1980s and has since become non-migratory. Over a two-year study of each population’s breeding season, we found no difference in the ratios of heterophils to lymphocytes between populations. However, urban residents had more leukocytes than birds from the altitudinal migrant population. A multivariate analysis suggested urban residents had fewer monocytes, but effect sizes were small. These results suggest no differences in energy demands or stressors between urban resident and altitudinal migrant populations during their breeding season. However, urban residency may confer immunological benefits through anthropogenic resources, which could have important consequences for disease dynamics..

About this journal

Animal Migration was an open-access journal that published cutting-edge research on the biology of migratory species. We strived to present a forum where all aspects of migratory biology can be discussed, from genetics and physiology to ecosystem-level interactions between migrants and their environment and everything in between.

The journal is closed for submissions.

The journal was published in Open Access model and is archived in Portico.

All authors retain copyright, unless – due to their local circumstances – their work is not copyrighted. The copyrights are governed by the Creative-Commons license.

Why read

Animal Migration publishes research on all species and all aspects of migration biology, keeping readers up to date on developments in non-focal species and systems.
We publish articles about new technologies and methods for studying migratory animals, providing readers with techniques they can use in their focal systems.
We feature research performed by individuals all over the globe, helping readers to connect with potential collaborators and correspondents.

The journal was edited by:
Journal Editor
Andrew K. Davis, University of Georgia, USA