Ecomorphology of the External Flight Apparatus of Blackcaps (Sylvia atricapilla) with Different Migration Behavior

Abstract

An analysis of the external flight apparatus of 700 blackcaps from eight different populations (sedentary to long-distance migrators) is presented. With increasing migration distances of populations, (1) wing length, aspect ratio, and wing pointedness increase; (2) wing load decreases; (3) slots on the wing tips become relatively shorter; (4) the alula tends to be shorter in relation to wing length; and (5) the tail is shorter in relation to wing length. Although body mass increases from southern to northern populations, changes in wing length and wing area are two to three times larger than expected for simple isometric relationships. Regarding the aerodynamic background of these changes, it can be stated that traits for energy-effective flight are more strongly developed and traits for maneuverability are less developed in birds traveling longer distances, presumably as a consequence of trade-offs. Nonmigratory blackcaps from Madeira and the Cape Verde islands do not always show the traits we would expect in view of their sedentary behavior. This can be seen as a result of recent colonization of these islands by migrants or of selection by factors other than migration behavior. In migratory populations, changes between the first and the second set of primaries during first complete molt show almost the same pattern as the changes from nonmigratory to migratory populations. During molt of the primaries, blackcaps of nonmigratory populations do not show these changes. Hybrids between migrating and nonmigrating blackcap populations (Moscow and Madeira) showed intermediate values between parent populations in wing length, wing shape, and wing area; in the other variables they resembled either parent population.

Morphological sexing of passerines: not valid over larger geographical scales

“…There are no data on habitat types of the study sites considered, thus this influence cannot be excluded, but Cuadrado (1991) explained the low probability of sexing wintering Robins correctly in Spain with the inclusion of birds with different migratory behaviour into the study. It has been discussed that migration distance is linked with wing length (Leisler andWinkler 2003), andFiedler (2005) showed on an intra-specific level that Blackcaps with increasing migratory distances have longer wings. Therefore, site-specific morphology as an adaptation to different migratory behaviour is presumably the main reason why morphological sexing cannot be applied over larger geographic scales.…”

“…Second, there are intra-specific differences in morphology due to different migration distances or other ecological factors (temperature, habitat) mainly varying across latitudes. In migratory species, those populations with a relatively longer migration distance usually have longer wings compared to populations with relatively shorter migration distance as shown, e.g., for the Willow Warbler (Lindström et al 1996) or the Blackcap Sylvia atricapilla (Fiedler 2005).…”

“…Birds migrating through the study area from more northern latitudes may have a different wing morphology compared to resident conspecifics because of adaptation to different migration distance (Leisler and Winkler 2003;Fiedler 2005). Therefore, we tested whether day of the season is associated with the morphological measurements with a one-way ANOVA with feather, wing, tarsus and body mass as dependent variables and day of the season (30 June = 1, 1 July = 2, etc.)…”

Convergence of broad-scale migration strategies in terrestrial birds

“…The resulting selection pressures have generated a unique set of morphological, physiological, and behavioural adaptations [5][6][7], whose quality varies based on the rigors of the migratory journey. For example, individuals that migrate longer distances tend to have adaptations that improve the efficiency of migratory flight [8][9][10]. The presence of geographical barriers to migration is an additional factor that may affect the quality of these adaptations.…”

Comparability of Wing Length Measurements Based on Data Collected at two Twin Stations during Migration

“…Busse 1968Busse , 1988Busse , 1997Busse , 1999Busse and Maksalon 1986;Lo Valvo et al 1988;Tellería and Carbonell 1999;Nowakowski 2000Nowakowski , 2002Tellería 2001, 2002;Yom-Tov et al 2006;Zaniewicz and Busse 2008;Salewski et al 2010;Van Buskirk et al 2010;Kovács et al 2010Kovács et al , 2012Arizaga et al 2012). However, clear dependencies are usually hidden, as the variation in wing length depends on several factors, such as sex, age, population, status of the specimen (skin, live bird) (Svensson 1992, Jenni and Winkler 1994, Fiedler 2005. Some additional variation is also caused by different habits of individual ringers who take measurements (Barrett et al 1989, Morgan 2004.…”