Integrity of and damage to wings, feather vanes and serrations in barn owls

A Comparison of Aerodynamic Parameters in Two Subspecies of the American Barn Owl (Tyto furcata)

Simple Summary

Morphology and function depend on the ecological niche in which an animal lives. Barn owls, occurring on all continents, occupy a nocturnal niche. These birds prey mainly on small rodents but include other small vertebrates and invertebrates in the diet. The size of the barn-owl species and subspecies varies considerably. The American continent harbors the species Tyto furcata. The body mass of the subspecies in North America (T.f.pratincola) is about a factor of two higher than that of the subspecies living on the Galapagos archipelago (T.f.puncatissima). We asked how this difference translates into aerodynamic parameters. The key question was whether there is so-called similarity scaling or not. In other words, whether important aerodynamic parameters scale according to body mass. This is called isometric scaling. Deviation from isometric scaling is called allometric scaling. If we use the subspecies from the continent as a reference, we find that the Galapagos barn owl has relatively larger wings than expected from isometric scaling. This translates into a lower wing loading in punctatissima than in pratincola. A lower wing loading means higher maneuverability. We speculate that the higher maneuverability allows the Galapagos owl to catch smaller prey, especially insects.

Abstract

Aerodynamic parameters, such as wing loading, are important indicators of flight maneuverability. We studied two subspecies of the American Barn owl (Tyto furcata), the North American subspecies, T.f.pratincola, and the Galapagos subspecies, T.f.punctatissima, with respect to aerodynamic parameters and compared our findings with those in other owl and bird species. The body mass of T.f.pratincola is about two times higher than that of T.f.punctatissima. Wing loading between the two subspecies scales allometrically. Wing loading in T.f.pratincola is about 50% higher than in T.f.punctatissima. The scaling of wing length is not statistically different from the prediction for isometric scaling. By contrast, the wing chord in T.f.punctatissima is larger than predicted by isometric scaling, as is the wing area. The scaling of wing loading observed here for T.f.punctatissima differs considerably from the scaling in other owl and bird species as available in the literature. We speculate that the allometric scaling helps T.f.punctatissima to catch smaller prey such, as insects that are found in many pellets of T.f.punctatissima, despite the fact that in both subspecies, small rodents make up most of the diet.

White plumage color as an honest indicator: feather macrostructure links reflectance with reproductive effort and success

Abstract

The structural condition of feathers may generally have a decisive role in shaping the color properties of the plumage. However, the information content of structurally mediated color differences is poorly known. This makes it particularly hard to determine the meaning of color variation in pigment-free white plumage patches. The white wing patch of the collared flycatcher (Ficedula albicollis) is an important sexual trait, and changes in its reflectance are partly due to macrostructural condition. We used 2 years of macrostructural, reflectance, and breeding data from both sexes to examine whether wing patch macrostructure lends information content to actual reflectance in terms of reproductive effort and success. Macrostructure strongly predicted actual reflectance in males but only weakly in females. Furthermore, in males, feather vane width was related positively to current year reproductive effort, and negatively to previous year reproductive effort. This indicates that macrostructurally mediated reflectance attributes may inform the receiver not only of actual reproductive capacity but also of individual quality via reproductive costs.

Significance statement

Coloration of animals takes a central place in their communication and in advertising reproductive abilities. Although white plumage is widespread among animals, usually we have little knowledge on how its structure is linked to reproduction. We investigated this link in a wild population of collared flycatchers. We demonstrated that white feather structure was related to coloration and with current year and previous year reproductive capabilities in males. Our results suggest that white feather structure has the potential to connect reproductive costs with coloration.