Heritable variation in circulating glucocorticoids and endocrine flexibility in a free-living songbird.

Phenotypic flexibility is a central way that organisms cope with challenging and changing environments. As endocrine signals mediate many phenotypic traits, heritable variation in hormone levels, or their context-dependent flexibility, could present an important target for selection. Several studies have estimated the heritability of circulating glucocorticoid levels under acute stress conditions, but little is known about the potential for either baseline hormone levels or rapid endocrine flexibility to evolve. Here, we assessed the potential for selection to operate on the elevation (circulating hormone levels) and flexibility of glucocorticoid reaction norms to acute restraint stress. Multivariate animal models revealed low but significant heritability in baseline (h2  = 0.13-0.14) and stress-induced glucocorticoids (h2  = 0.18), and moderate heritability in glucocorticoid flexibility in response to acute stress (h2  = 0.38) in free-living juvenile tree swallows (Tachycineta bicolor; n = 408). Baseline glucocorticoids were not genetically correlated with either stress-induced glucocorticoids or glucocorticoid flexibility. These findings indicate that baseline glucocorticoids and the acute stress response are distinct traits that can be independently shaped by selection. Microevolutionary changes that influence the expression or flexibility of these endocrine mediators of phenotype may be an important way that populations adapt to changing environments and novel threats.

Real-time in vivo uric acid biosensor system for biophysical monitoring of birds.

Research on birds has long played an important role in ecological investigations, as birds are relatively easily observed, and their high metabolic rates and diurnal habits make them quite evidently responsive to changes in their environments. A mechanistic understanding of such avian responses requires a better understanding of how variation in physiological state conditions avian behavior and integrates the effects of recent environmental changes. There is a great need for sensor systems that will allow free-flying birds to interact with their environment and make unconstrained decisions about their spatial location at the same time that their physiological state is being monitored in real time. We have developed a miniature needle-based enzymatic sensor system suitable for continuous real-time amperometric monitoring of uric acid levels in unconstrained live birds. The sensor system was constructed with Pt/Ir wire and Ag/AgCl paste. Uricase enzyme was immobilized on a 0.7 mm sensing cavity of Nafion/cellulose inner membrane to minimize the influences of background interferents. The sensor response was linear from 0.05 to 0.6 mM uric acid, which spans the normal physiological range for most avian species. We developed a two-electrode potentiostat system that drives the biosensor, reads the output current, and wirelessly transmits the data. In addition to extensive characterization of the sensor and system, we also demonstrate autonomous operation of the system by collecting in vivo extracellular uric acid measurements on a domestic chicken. The results confirm our needle-type sensor system's potential for real-time monitoring of birds' physiological state. Successful application of the sensor in migratory birds could open up a new era of studying both the physiological preparation for migration and the consequences of sustained avian flight.

Movement ecology of migration in turkey vultures.

We develop individual-based movement ecology models (MEM) to explore turkey vulture (Cathartes aura) migration decisions at both hourly and daily scales. Vulture movements in 10 migration events were recorded with satellite-reporting GPS sensors, and flight behavior was observed visually, aided by on-the-ground VHF radio-tracking. We used the North American Regional Reanalysis dataset to obtain values for wind speed, turbulent kinetic energy (TKE), and cloud height and used a digital elevation model for a measure of terrain ruggedness. A turkey vulture fitted with a heart-rate logger during 124 h of flight during 38 contiguous days showed only a small increase in mean heart rate as distance traveled per day increased, which suggests that, unlike flapping, soaring flight does not lead to greatly increased metabolic costs. Data from 10 migrations for 724 hourly segments and 152 daily segments showed that vultures depended heavily upon high levels of TKE in the atmospheric boundary layer to increase flight distances and maintain preferred bearings at both hourly and daily scales. We suggest how the MEM can be extended to other spatial and temporal scales of avian migration. Our success in relating model-derived atmospheric variables to migration indicates the potential of using regional reanalysis data, as here, and potentially other regional, higher-resolution, atmospheric models in predicting changing movement patterns of soaring birds under various scenarios of climate and land use change.

Experimental evidence for offspring learning in parent-offspring communication.

The offspring of birds and mammals solicit food from their parents by a combination of movements and vocalizations that have come to be known collectively as 'begging'. Recently, begging has most often been viewed as an honest signal of offspring need. Yet, if offspring learn to adjust their begging efforts to the level that rewards them most, begging intensities may also reflect offsprings' past experience rather than their precise current needs. Here we show that bird nestlings with equal levels of need can learn to beg at remarkably different levels. These experiments with hand-raised house sparrows (Passer domesticus) indicated that chicks learn to modify begging levels within a few hours. Moreover, we found that the begging postures of hungry chicks in natural nests are correlated with the average postures that had previously yielded them parental feedings. Such learning challenges parental ability to assess offspring needs and may require that, in response, parents somehow filter out learned differences in offspring signals.

Isolation and characterization of microsatellite markers from three species of swallows in the genus Tachycineta: T. albilinea, T. bicolor and T. leucorrhoa.

We describe 30 microsatellite loci developed from three species of swallows in the genus Tachycineta: T. bicolor (tree swallow), T. albilinea (mangrove swallow), and T. leucorrhoa (white-rumped swallow). These commonly studied birds nest in secondary cavities and are distributed from Alaska to Argentina. Primer pairs were designed for each species individually and tested for cross-amplification in 40-48 individuals of all three species. Polymorphism ranged from 5 to 65 alleles per locus (mean = 19.1). These markers will allow comparative studies of extra-pair paternity rates among members of the genus as well as the assessment of population structure.

Evolution of nest construction in swallows (Hirundinidae): a molecular phylogenetic perspective.

Nest construction is more diverse in the Hirundinidae than in any other family of oscine birds. To explore the evolution of this diversity, we superimposed nest data on a DNA-hybridization phylogeny of 17 swallow species. Nest construction is tightly linked to the inferred evolutionary history. Burrowing appears to be the primitive nesting mode, and burrowing ancestors gave rise to cavity-adopting and mud-nesting clades. Obligate cavity adoption is mostly confined to a monophyletic clade in the New World, and the diversification of obligate nest adopters appears to be tied to the richness of forest habitats and recent active mountain building there. Construction of mud nests originated only once in the history of the group, and mud-nesters have diversified principally in Africa, where a drier climatic history has favored their mode of nesting. The use of pure mud to construct a hanging nest is unique among all birds, and we infer that mud nests have increased in complexity during evolution from simple mud cups to fully enclosed retort-shaped nests. This increased complexity appears to have been the critical precursor for the evolution of high-density colonial mud-nesters.

Flock-feeding on fish schools increases individual success in gulls.

Flock-foraging and the role of white plumage in gulls and other seabirds have been the subject of much debate. At first sight it seems that competition within the flock would render flock formation against the interest of the bird who finds the fish school, as the fish must then be shared with birds joining the flock. However, it is also possible that flock formation is neutral or even beneficial to the individual members, including the bird that found the fish (the 'first finder'). Here we show that the fishing success of individual black-headed gulls, Larus ridibundus, increases with flock size up to at least eight birds. Part of the reason is that the fish school is more vulnerable when attacked by several gulls. The first gull to reach a fish school therefore benefits from being joined by others, and conspicuous white upper parts in gulls may act as a means of attracting other gulls to the flock and hence improving hunting success.

A comparison of cytochrome b and DNA hybridization data bearing on the phylogeny of swallows (Aves: Hirundinidae).

Cytochrome b sequence data from 17 species representing 16 genera of swallows (Aves: Hirundinidae) were compared with DNA-DNA hybridization data from the same species in a taxonomic congruence assessment of swallow phylogeny. In the process, subsets (partitions) of the cytochrome b sequence data were examined in light of the DNA hybridization distances to assess their potential phylogenetic informativeness. When the sequence data were weighted-with or without reference to the DNA hybridization data-they produced parsimony and maximum likelihood (but not distance) trees that were largely congruent with the DNA hybridization tree. To this extent, the cytochrome b data supported many of the phylogenetic conclusions based on the DNA hybridization tree and vice versa. However, the cytochrome b data produced largely unresolved trees when branch robustness was tested by bootstrapping and other methods. This poor resolution appeared to be caused by a lack of hierarchical structure in the cytochrome b distances, which were confined to a narrow range (between 10-13%), compressed by saturation, and noisy. Partition analysis by codon sites and protein domains yielded typical avian cytochrome b patterns, except for idiosyncrasies attributable to the genetic divergence level of swallows in comparison to other groups of birds whose cytochrome b sequences have been analyzed.