No abstract

Many organizations have installed artificial burrows to help bolster local Burrowing Owl (Athene cunicularia) populations. However, occupancy probability and reproductive success in artificial burrows varies within and among burrow installations. We evaluated the possibility that depth below ground might explain differences in occupancy probability and reproductive success by affecting the temperature of artificial burrows. We measured burrow temperatures from March to July 2010 in 27 artificial burrows in southern California that were buried 15–76 cm below the surface (measured between the surface and the top of the burrow chamber). Burrow depth was one of several characteristics that affected burrow temperature. Burrow temperature decreased by 0.03°C per cm of soil on top of the burrow. The percentage of time that artificial burrows provided a thermal refuge from above‐ground temperature decreased with burrow depth and ranged between 50% and 58% among burrows. The percentage of time that burrow temperature was optimal for incubating females also decreased with burrow depth and ranged between 27% and 100% among burrows. However, the percentage of time that burrow temperature was optimal for unattended eggs increased with burrow depth and ranged between 11% and 95% among burrows. We found no effect of burrow depth on reproductive success across 21 nesting attempts. However, occupancy probability had a non‐linear relationship with burrow depth. The shallowest burrows (15 cm) had a moderate probability of being occupied (0.46), burrows between 28 and 40 cm had the highest probability of being occupied (>0.80), and burrows >53 cm had the lowest probability of being occupied (<0.43). Burrowing Owls may prefer burrows at moderate depths because these burrows provide a thermal refuge from above‐ground temperatures, and are often cool enough to allow females to leave eggs unattended before the onset of full‐time incubation, but not too cool for incubating females that spend most of their time in the burrow during incubation. Our results suggest that depth is an important consideration when installing artificial burrows for Burrowing Owls. However, additional study is needed to determine the possible effects of burrow depth on reproductive success and on possible tradeoffs between the effects of burrow depth on optimal temperature and other factors, such as minimizing the risk of nest predation.

BackgroundMillions of flying migrants encounter the Great Lakes and other large water bodies on long-distance flights each spring and fall, but quantitative data regarding how they traverse these obstacles are limited. Shorelines are known areas of migrant concentration due to the ecological barrier effect, but details on the magnitude of this concentration and the flight behaviors causing it are largely unknown and difficult to quantify. Mobile avian radar can provide a unique view of how birds and bats move across landscapes by tracking thousands of individual migrants moving through a sample volume that extends multiple kilometers in radius.ResultsDuring the spring of 2014 we used two avian radar units to compare migration patterns at shoreline (1.5 km from the shore) and inland (20 km from the shore) sites along the eastern shoreline of Lake Michigan in the north-central US. We found shoreline activity to be 27% greater than inland activity over all time periods, and 132% greater during the hour surrounding dawn. An analysis of flight directions found that migrants flew to the north and northwest during dusk and night, with many heading out over the lake, but shifted direction towards the east at dawn, as those flying over water reoriented towards land. This shift in direction, which was most intense at the shoreline, may contribute to the higher concentrations of migrants observed at shorelines in this study and others.ConclusionsThese findings help confirm and quantify the phenomenon of nocturnal migrant reorientation at dawn, and also stress the functional importance of coastal regions for aerial migrants. The high use of coasts by migrants highlights the importance of conserving shoreline stopover habitat, which often competes with anthropogenic uses. We suggest using a high degree of caution when assessing potential impacts from development in these sensitive environments, and encourage protection of these high-use areas.Electronic supplementary materialThe online version of this article (10.1186/s40462-018-0135-3) contains supplementary material, which is available to authorized users.

Sexual selection can drive the evolution of conspicuous visual signals that advertise individual quality to prospective mates. Reproductive strategy can influence the balance between selective pressures and whether sexually selected signals evolve. Alternatively, visual signals can serve other functions, including predator deterrence, species recognition and differentiating genetically determined morphs. In the dimorphic white-throated sparrow (Zonotrichia albicollis), we explored how selection on conspicuous colouration changes with reproductive strategy, and whether visual signals of morph identity are discrete from sexually selected signals of individual quality. In this species, white morph birds have more colourful plumage than tan morph birds, and white males are more promiscuous and aggressive than tan counterparts. White females are also more aggressive than tan females. White males with more contrasting colouration achieved higher lifetime fitness, whereas the opposite relationship occurred among tan males. Linear selection gradients indicated strong, positive selection on plumage contrast in white males, but negative selection on contrast in tan males. For both morphs, relationships between female colouration and fitness were weak. Results demonstrate disruptive selection on a visual signaling trait in a colour polymorphic species and suggest that signals associated with an aggressive morph can also evolve to indicate individual quality within that morph.

Millions of migrants encounter the Great Lakes during spring and autumn migratory movements. How migrants behave when encountering these lakes is relatively unknown at the local and basin scales. Using seven years of radar data from 33 sites along the Great Lakes coastline, we investigated three hypotheses on migrant behavior during crepuscular and nocturnal movements. First, we hypothesized migrants' direction is driven by local geography and its relation to the destination of migration. Second, we hypothesized migrants would move toward shore at dawn. Finally, we hypothesized that the Great Lakes would have different directional movements at lakes on the outside of the basin versus the interior. We found partial support for our first hypothesis, as well as evidence of decision making when migrants first encounter the Great Lakes. We found partial support for our second hypothesis. We found that migrants moved toward land at elevated levels at dawn compared to night during fall migration, but no effect was found during spring. We found support for our final hypothesis during spring migration, but not during fall. This pattern may be because of a combination of geographical, biological, and data bias, and will require additional work to disentangle. Taken together, we found that migrants perceive and react to the Great Lakes, and attempt to decrease risk, perceived or real, as they make their way to their migratory destination. Better understanding of directional movement has conservation implications, including mitigating anthropogenic obstacle collision risk and prioritizing stopover habitat restoration. Les oiseaux migrateurs utilisent des stratégies mixtes pour traverser le bassin des Grands LacsRÉSUMÉ. Des millions d'oiseaux croisent les Grands Lacs au cours des déplacements migratoires de printemps et d'automne. Le comportement des migrateurs lorsqu'ils rencontrent ces lacs est relativement inconnu à l'échelle locale et celle du bassin. En utilisant sept années de données radar provenant de 33 sites le long des côtes des Grands Lacs, nous avons examiné trois hypothèses sur le comportement des migrateurs pendant les déplacements crépusculaires et nocturnes. Notre première hypothèse veut que la direction des migrateurs soit déterminée par la géographie locale et sa relation avec la destination de la migration. Notre deuxième hypothèse stipule que les migrateurs se déplaceraient vers la côte à l'aube. Enfin, notre dernière hypothèse suppose que les déplacements directionnels au-dessus des Grands Lacs seraient différents selon que les lacs se trouvent à l'extérieur ou à l'intérieur du bassin. Notre première hypothèse a obtenu un soutien partiel, et nous avons trouvé des indices de prise de décision lorsque les migrateurs rencontrent les Grands Lacs pour la première fois. Notre deuxième hypothèse a aussi reçu un soutien partiel : nous avons constaté que les migrateurs se déplaçaient vers la terre ferme à des taux élevés à l'aube par rapport à la nuit pendant la migration d'automne, mais aucun effet n'a été const...