New methods for estimating the total wing area of birds.

Dispersal is a fundamental process in evolution and ecology. Due to the predominant role of flight in bird movement, their dispersal capabilities can be estimated from their flight morphology. Most predictors of flight efficiency require an estimate of the total wing area, but the existing methods for estimating wing area are multi-stepped and prone to compounding error. Here, we validated a new method for estimating the total wing area that requires only the measurement of the wingspan plus two measurements from the folded wings of study skin specimens: wing length and wing width. We demonstrate that the new folded-wing method estimates total wing area with high precision across a variety of avian groups and wing shapes. In addition, the new method performs as well as the old method when used to estimate natal dispersal distances of North American birds. The folded-wing method will allow for estimates of the total wing to be readily obtained from thousands of specimens in ornithological collections, thus providing critical information for studies of flight and dispersal in birds.

La dispersión es un proceso fundamental en evolución y ecología. Debido al papel predominante del vuelo en el movimiento de las aves, su capacidad de dispersión puede estimarse a partir de su morfología de vuelo. La mayoría de los predictores de la eficiencia de vuelo requieren una estimación del área total del ala, pero los métodos existentes para estimar el área del ala requieren numerosos pasos y son propensos a errores compuestos. En este estudio validamos un nuevo método para estimar el área total del ala que requiere solo la medida de la envergadura y dos medidas de las alas plegadas que pueden tomarse de pieles del estudio: el largo y el ancho del ala. Demostramos que el nuevo método estima el área total del ala con alta precisión en una variedad de grupos de aves y formas de alas. Además, el nuevo método funciona tan bien como el anterior cuando se usa para estimar las distancias de dispersión natal de las aves de América del Norte. El nuevo método permitirá obtener fácilmente estimaciones del área alar total a partir de miles de especímenes en colecciones ornitológicas, beneficiando estudios de vuelo y dispersión en aves.

Determinants of natal dispersal distances in North American birds.

Natal dispersal-the movement from birth site to first breeding site-determines demographic and population genetic dynamics and has important consequences for ecological and evolutionary processes. Recent work suggested that one of the main factors determining natal dispersal distances is the cost of locomotion. We evaluated this hypothesis using band recovery data to estimate natal dispersal distances for 50 North American bird species. We then analyzed the relationships between dispersal distances and a suite of morphological and ecological predictors, including proxies for the cost of locomotion (flight efficiency), using phylogenetic regression models. We found that flight efficiency, population size, and habitat influence natal dispersal distances. We discuss how the effects of population size and habitat can also be related to mobility and locomotion. Our findings are consistent with a predominant effect of adaptations for mobility on dispersal distances.

Community science reveals links between migration arrival timing advance, migration distance and wing shape.

Substantial global data show that many taxa are shifting their phenologies in response to climate change. For birds, migration arrival dates in breeding regions have been shifting earlier, and there is evidence that both evolutionary adaptation and behavioural flexibility influence these shifts. As more efficient flyers may be able to demonstrate more flexibility to respond to changing conditions during migratory flight, we hypothesize that differences among passerine species in flight efficiency, as reflected by morphology, may be associated with the magnitude of shifts in arrival date in response to climate warming. We applied a logistic model to 18 years of eBird data to estimate mean arrival date for 44 common passerines migrating to northeast North America. We then used linear mixed-effects models to estimate changes in mean arrival date and compared these changes to morphological proxies for flight efficiency and migratory distance using phylogenetic generalized least squares models. On average, passerine species shifted their arrival dates 0.120 days earlier each year, with 27 of the 44 species shifting to significantly earlier arrival times, and two shifting to significantly later ones. Of the 15 species with non-significant shifts, 13 trended toward earlier arrivals. Longer migration distances and higher wing aspect ratios were associated with greater shifts toward earlier arrivals. Migration distance and aspect ratio were also significantly correlated to each other. This suggests that changes in arrival date are affected by factors pertaining to migratory flight over long distances namely, flight efficiency and migration distance. These traits may be able predict the magnitude of arrival date shift, and by extension identify species that are most at risk to climate change due to inflexible arrival timing.