Non-random distribution of individual genetic diversity along an environmental gradient

Improving our knowledge of the links between ecology and evolution is especially critical in the actual context of global rapid environmental changes. A critical step in that direction is to quantify how variation in ecological factors linked to habitat modifications might shape observed levels of genetic variability in wild populations. Still, little is known on the factors affecting levels and distribution of genetic diversity at the individual level, despite its vital underlying role in evolutionary processes. In this study, we assessed the effects of habitat quality on population structure and individual genetic diversity of tree swallows (Tachycineta bicolor) breeding along a gradient of agricultural intensification in southern Québec, Canada. Using a landscape genetics approach, we found that individual genetic diversity was greater in poorer quality habitats. This counter-intuitive result was partly explained by the settlement patterns of tree swallows across the landscape. Individuals of higher genetic diversity arrived earlier on their breeding grounds and settled in the first available habitats, which correspond to intensive cultures. Our results highlight the importance of investigating the effects of environmental variability on individual genetic diversity, and of integrating information on landscape structure when conducting such studies.     

Restoration and management for cliff‐nesting birds in Mediterranean mining sites: the Sand Martin case study

Habitat enhancement for birds is frequently implemented during mine site restoration. Cliff‐nesting birds often colonize anthropogenic environments such as mining areas (aggregate sites and quarries for aggregate and cement production). Mining activity can compromise breeding success, causing cliff‐nesting birds to depend on the management and restoration of mining areas. The objective of our study is to assess the importance of mine site habitats for Sand Martin conservation and reconcile mining activity with breeding success in Mediterranean environments. We studied Sand Martin breeding habitat preferences in mining areas at three spatial scales. At the mining site scale, we compared 10 mining sites with Sand Martin burrows with 19 mining sites without burrows. At the colony scale (vertical structures with colonies), we evaluated the relationships between the number of breeding pairs, number of burrows, and colony characteristics within 30 distinct Sand Martin colonies. At the burrow scale, we compared the characteristics of the available vertical structure with the areas used by Sand Martins. At the mining site scale, Sand Martins preferred more surface of water bodies, shorter distances to flowing water, older sites, and mining sites which produce aggregates instead of cement. At the colony scale, Sand Martins preferred southwest orientations and stockpiles to vertical extraction faces. At the burrow scale, birds preferred the most vertical areas of the face. Our results support the need for effective habitat restoration and improved management for more effective Sand Martin conservation within mining areas. Simple interventions can enhance habitat quality and conservation of cliff‐nesting birds.     

Feather steroid hormone concentrations in relation to age,sex, and molting time in a long‐distance migratory passerine

In birds, concentrations of testosterone (T) and corticosterone (Cort) are closely connected with many morphological, behavioral, and other physiological traits, including reproduction, metabolism, immunity, and fitness. The direction of the effect of these hormones on above‐mentioned traits, and the potential feedback between hormones are in general unclear; in addition, knowledge on how age and sex can affect T and Cort concentrations is still inconsistent. Our study used a novel method to analyze testosterone and corticosterone in feathers (T_f, Cort_f) based on the precolumn chemical derivatization of hormones before liquid chromatography–tandem mass spectrometry (LC‐MS/MS) analysis. Unlike previously used methods (RIA, EIA), our analytical procedure allows simultaneous analysis of both hormones from small amounts of feathers (4–25 mg) and, thus, overcomes the problem of insufficient detection limits. We applied this method to reveal associations between T_f and Cort_f hormone concentrations and feather growth, age, and sex in feathers grown during the postbreeding (flanks) and prebreeding (tails) periods in barn swallows (Hirundo rustica). There was neither a correlation between prebreeding and postbreeding T_f, nor between prebreeding and postbreeding Cort_f. Tail Cort_f concentrations were negatively associated with tail feather growth rates. Feather hormone concentrations were correlated in the prebreeding period, negatively in males but positively in females. Both Cort_f and T_f were higher in young birds compared to older ones, indicating either an age‐related decrease in hormone concentrations within individuals, or the selective disappearance of individuals with high steroid concentrations. Males and females did not differ in Cort_f, but T_f concentrations were higher in males than females, particularly during the prebreeding period. In this study, we provide an effective method for analyzing hormones in feathers in an ecological context, especially in situations when the total amount of feathers available for the analysis is limited.     

The stress of parenthood? Increased glucocorticoids in birds with experimentally enlarged broods

Variation in baseline glucocorticoid (cort) levels can be attributed, at least in part, to differences in energetic demands confronting individuals. Elevated baseline cort levels are routinely interpreted as indicating individuals in poor condition, with low relative fitness. However, when greater reproductive effort increases energetic demands, individuals with high cort might paradoxically be those with the highest fitness. Here, we experimentally test the hypothesis that increased reproductive demand causes increases in baseline cort (the Cort-Adaptation hypothesis). We measured maternal baseline cort before and after experimentally enlarging and reducing brood sizes in tree swallows (Tachycineta bicolor). Females with experimentally enlarged broods had greater increases in baseline cort and fledged more offspring than females with reduced broods. Additionally, females with greater increases in baseline cort had higher offspring-provisioning rates than females with lower changes in cort. These findings demonstrate that increased reproductive demand can cause increased baseline cort. As yet, we do not know if these increases in cort cause increased allocation of resources towards reproduction, but the positive relationship between parental behaviour and cort suggests that increased cort does not always interfere with reproductive investment, and might instead facilitate it.     

Feather holes and flight performance in the barn swallow Hirundo rustica

Feather holes are small (0.5–1?mm in diameter) deformities that appear on the vanes of flight feathers. Such deformities were found in many bird species, including galliforms and passerines. Holey flight feathers may be more permeable to air, which could have a negative effect on their ability to generate aerodynamic forces. However, to date the effects of feather holes on flight performance in birds remained unclear. In this study we investigated the relationship between the number of feather holes occurring in the wing or tail feathers and short term flight performance traits – aerial manoeuvrability, maximum velocity and maximum acceleration – in barns swallows, which are long distance migrating aerial foragers. We measured short-term flight performance of barn swallows in a standardized manner in flight tunnels. We found that acceleration and velocity were significantly negatively associated with the number of holes in the wing flight feathers, but not with those in the tail feathers. In the case of acceleration the negative relationship was sex specific – while acceleration significantly decreased with the number of feather holes in females, there was no such significant association in males. Manoeuvrability was not significantly associated with the number of feather holes. These results are consistent with the hypothesis that feather holes are costly in terms of impaired flight. We discuss alternative scenarios that could explain the observed relationships. We also suggest directions for future studies that could investigate the exact mechanism behind the negative association between the number of feather holes and flight characteristics.     

Viability and expression of sexual ornaments in the barn swallow Hirundo rustica: a meta‐analysis

Sexual selection results in the evolution of exaggerated secondary sexual characters that can entail a viability cost. However, in species where sexual ornaments honestly reflect individual quality, the viability cost of secondary sexual characters may be overwhelmed by variation in individual quality, leading to expect that individuals with the largest secondary sexual characters show higher, rather than lower viability. Here, we used meta‐analyses to test whether such expected positive relationship between sexual ornamentation and viability exists in the barn swallow Hirundo rustica, which is one of the most studied model species of sexual selection under field conditions. We found a mean positive effect size of viability in relation to the expression of secondary sexual characters of 0.181 (CI: 0.084–0.278), indicating that in this species the more ornamented individuals are more viable, and therefore of high quality. Analyses of moderator variables showed similar effects in males and females, the H. r. rustica subspecies rather than others and tail length rather than other secondary sexual characters. Future research emphasis on other subspecies than the European one and secondary sexual characters than tail length may help identify the sources of heterogeneity in effect sizes.