Demographic partitioning of dynamic energy subsidies revealed with an Ornstein-Uhlenbeck space use model.

In populations across many taxa, a large fraction of sexually mature individuals do not breed but are attempting to enter the breeding population. Such individuals, often referred to as "floaters," can play critical roles in the dynamics and stability of these populations and buffer them through periods of high adult mortality. Floaters are difficult to study, however, so we lack data needed to understand their roles in the population ecology and conservation status of many species. Here, we analyzed satellite telemetry data with a newly developed mechanistic space use model based on an Ornstein-Uhlenbeck process to help overcome the paucity of data in studying the differential habitat selection and space use of floater and territorial golden eagles Aquila chrysaetos. Our sample consisted of 49 individuals tracked over complete breeding seasons across 4 years, totaling 104 eagle breeding seasons. Modeling these data mechanistically was required to disentangle key differences in movement and particularly to separate aspects of movement driven by resource selection from those driven by use of a central place. We found that floaters generally had more expansive space use patterns and larger home ranges, as well as evidence that they partition space with territorial individuals seemingly on fine scales through differential habitat and resource selection. Floater and territorial eagle home ranges overlapped markedly, suggesting that floaters use the interstices between territories. Furthermore, floater and territorial eagles differed in how they selected for uplift variables, key components of soaring birds' energy landscape, with territorial eagles apparently better able to find and use thermal uplift. We also found relatively low individual heterogeneity in resource selection, especially among territorial individuals, suggesting a narrow realized niche for breeding individuals, which varied from the level of among-individual variation present during migration. This work furthers our understanding of floaters' potential roles in the population ecology of territorial species and suggests that conserving landscapes occupied by territorial eagles also protects floaters.

Novel step selection analyses on energy landscapes reveal how linear features alter migrations of soaring birds.

Human modification of landscapes includes extensive addition of linear features, such as roads and transmission lines. These can alter animal movement and space use and affect the intensity of interactions among species, including predation and competition. Effects of linear features on animal movement have seen relatively little research in avian systems, despite ample evidence of their effects in mammalian systems and that some types of linear features, including both roads and transmission lines, are substantial sources of mortality. Here, we used satellite telemetry combined with step selection functions designed to explicitly incorporate the energy landscape (el-SSFs) to investigate the effects of linear features and habitat on movements and space use of a large soaring bird, the golden eagle Aquila chrysaetos, during migration. Our sample consisted of 32 adult eagles tracked for 45 spring and 39 fall migrations from 2014 to 2017. Fitted el-SSFs indicated eagles had a strong general preference for south-facing slopes, where thermal uplift develops predictably, and that these areas are likely important aspects of migratory pathways. el-SSFs also provided evidence that roads and railroads affected movement during both spring and fall migrations, but eagles selected areas near roads to a greater degree in spring compared to fall and at higher latitudes compared to lower latitudes. During spring, time spent near linear features often occurred during slower-paced or stopover movements, perhaps in part to access carrion produced by vehicle collisions. Regardless of the behavioural mechanism of selection, use of these features could expose eagles and other soaring species to elevated risk via collision with vehicles and/or transmission lines. Linear features have previously been documented to affect the ecology of terrestrial species (e.g. large mammals) by modifying individuals' movement patterns; our work shows that these effects on movement extend to avian taxa.

Local meteorological conditions reroute a migration.

For migrating animals, realized migration routes and timing emerge from hundreds or thousands of movement decisions made along migration routes. Local weather conditions along migration routes continually influence these decisions, and even relatively small changes in en route weather may cumulatively result in major shifts in migration patterns. Here, we analysed satellite tracking data to score a discrete navigation decision by a large migratory bird as it navigated a high-latitude, 5000 m elevation mountain range to understand how those navigational decisions changed under different weather conditions. We showed that wind conditions in particular areas along the migration pathway drove a navigational decision to reroute a migration; conditions encountered predictably resulted in migrants routing either north or south of the mountain range. With abiotic conditions continuing to change globally, simple decisions, such as the one described here, might additively emerge into new, very different migration routes.

Effects of developmental conditions on growth, stress and telomeres in black-legged kittiwake chicks.

Early-life conditions can drive ageing patterns and life history strategies throughout the lifespan. Certain social, genetic and nutritional developmental conditions are more likely to produce high-quality offspring: those with good likelihood of recruitment and productivity. Here, we call such conditions "favoured states" and explore their relationship with physiological variables during development in a long-lived seabird, the black-legged kittiwake (Rissa tridactyla). Two favoured states were experimentally generated by manipulation of food availability and brood size, while hatching order and sex were also explored as naturally generating favoured states. Thus, the favoured states we explored were high food availability, lower levels of sibling competition, hatching first and male sex. We tested the effects of favoured developmental conditions on growth, stress, telomere length (a molecular marker associated with lifespan) and nestling survival. Generation of favoured states through manipulation of both the nutritional and social environments furthered our understanding of their relative contributions to development and phenotype: increased food availability led to larger body size, reduced stress and higher antioxidant status, while lower sibling competition (social environment) led to lower telomere loss and longer telomere lengths in fledglings. Telomere length predicted nestling survival, and wing growth was also positively correlated with telomere length, supporting the idea that telomeres may indicate individual quality, mediated by favoured states.

Isotopic segregation between sympatric seabird species increases with nutritional stress.

Dietary segregation is essential for the coexistence of closely related species of animals. However, little is known about how changes in availability of food resources might affect trophic interactions of wild animals breeding in sympatry. Here, we examined how interannual variations in relative food availability (as reflected in blood levels of stress hormone corticosterone, CORT) affect food partitioning (assessed via a comparison of stable isotope δ(15)N and δ(13)C ratios of blood) between the common murre (Uria aalge) and thick-billed murre (Uria lomvia), breeding on a single colony in the Bering Sea. During a 6-year study, CORT varied among years but not between species, whereas stable isotope ratios varied among years and between species. Isotopic distance between species increased with increasing CORT. These results indicate that, when food was not limiting, both species relied on similar food resources. As foraging conditions deteriorated, murres diverged in their diets. We conclude that the degree of dietary segregation between Uria spp. varies with changes in the availability of food and is greatest during food shortages.

Phylogenetic and structural analysis of the HbA (alphaA/betaA) and HbD (alphaD/betaA) hemoglobin genes in two high-altitude waterfowl from the Himalayas and the Andes: Bar-headed goose (Anser indicus) and Andean goose (Chloephaga melanoptera).

Two species of waterfowl living at high altitude provide a prominent example of parallel adaptation at the molecular level. The bar-headed goose (Anser indicus) breeds at high elevations in central Asia and migrates across the Himalayas, where the partial pressure of oxygen (O(2)) is one-third of sea level. In South America, the distantly related Andean goose (Chloephaga melanoptera) is endemic to the high Andes. Both species exhibit increased blood-O(2) affinity, which has been attributed to the effects of single amino acid substitutions in the major hemoglobin. Here we present phylogenetic analyses of the swans and geese (Anserinae) and South American sheldgeese (Anatinae) using the three genes that encode the major (HbA) and minor (HbD) hemoglobin isoforms. We sought to determine whether two amino acid substitutions that have been the focus of extensive biochemical analysis (Ala-alpha(A)119 and Ser-beta(A)55) are uniquely derived in bar-headed goose and Andean goose, respectively, and to examine evidence of molecular adaptation at other positions in hemoglobin genes by comparing these two high-altitude taxa to their closest relatives. Bayesian analysis of the alpha(A)-, alpha(D)-, and beta(A)-subunit genes produced well-resolved phylogenies, with high posterior probabilities and bootstrap values for most genera. The bar-headed goose is likely sister to all other Anser species. Andean goose, the sole highland representative of the South American sheldgeese is either sister to the other Chloephaga species or sister to Neochen. In the bar-headed goose, four derived substitutions were observed in HbA (alpha(A)12, 18, 63, 119) and two in HbD (alpha(D)2, 47). Four derived substitutions in Andean goose include three in HbA (alpha(A)8, 77; beta(A)86) and two in HbD (alpha(D)9; beta(A)86). Considering both highland species, four substitutions (Ala-alpha(A)8, Ala-alpha(A)12, Ser-alpha(A)18, Leu-alpha(D)9) were located at adjacent positions on the A helix (or AB corner) of the alpha-chains, three others (Thr-alpha(A)77, Ser-beta(A)86, Ser-alpha(D)2) were in close proximity to inositolpentaphosphate (IP(5)) binding sites, and Ala-alpha(A)119 occurred at an alphabeta intersubunit contact. Ser-beta(A)55, which is involved in the same alphabeta intersubunit contact and was previously shown to increase Hb-O(2) affinity, is not unique to Andean goose, but is a synapomorphy of the South American sheldgeese, a clade of predominantly lowland waterfowl. Our findings illustrate the importance of understanding phylogenetic relationships and polarity of character-state changes when making inferences about adaptive evolution.

Signatures of high-altitude adaptation in the major hemoglobin of five species of andean dabbling ducks.

Hypoxia is one of the most important factors affecting survival at high altitude, and the major hemoglobin protein is a likely target of selection. We compared population genetic structure in the alphaA and betaA hemoglobin subunits (HBA2 and HBB) of five paired lowland and highland populations of Andean dabbling ducks to unlinked reference loci. In the hemoglobin genes, parallel amino acid replacements were overrepresented in highland lineages, and one to five derived substitutions occurred at external solvent-accessible positions on the alpha and beta subunits, at alpha(1)beta(1) intersubunit contacts, or in close proximity to inositolpentaphosphate (IPP) binding sites. Coalescent analyses incorporating the stochasticity of drift and mutation indicated that hemoglobin alleles were less likely to be transferred between highland and lowland populations than unlinked alleles at five other loci. Amino acid replacements that were overrepresented in the highlands were rarely found within lowland populations, suggesting that alleles segregating at high frequency in the highlands may be maladaptive in the lowlands and vice versa. Most highland populations are probably nonmigratory and locally adapted to the Altiplano, but gene flow for several species may be sufficiently high to retard divergence at unlinked loci. Heterozygosity was elevated in the alphaA or betaA subunits of highland populations exhibiting high gene flow between the southern lowlands and the highlands and in highland species that disperse seasonally downslope to midelevation environments from the central Andean plateau. However, elevated heterozygosity occurred more frequently in the alphaA subunit but not simultaneously in both subunits, suggesting that selection may be more constrained by epistasis in the betaA subunit. Concordant patterns among multiple species with different evolutionary histories and depths of historical divergence and gene flow suggest that the major hemoglobin genes of these five dabbling duck species have evolved adaptively in response to high-altitude hypoxia in the Andes.