Wind, Waves, and Wing Loading: Morphological Specialization May Limit Range Expansion of Endangered Albatrosses

Abstract

Among the varied adaptations for avian flight, the morphological traits allowing large-bodied albatrosses to capitalize on wind and wave energy for efficient long-distance flight are unparalleled. Consequently, the biogeographic distribution of most albatrosses is limited to the windiest oceanic regions on earth; however, exceptions exist. Species breeding in the North and Central Pacific Ocean (Phoebastria spp.) inhabit regions of lower wind speed and wave height than southern hemisphere genera, and have large intrageneric variation in body size and aerodynamic performance. Here, we test the hypothesis that regional wind and wave regimes explain observed differences in Phoebastria albatross morphology and we compare their aerodynamic performance to representatives from the other three genera of this globally distributed avian family. In the North and Central Pacific, two species (short-tailed P. albatrus and waved P. irrorata) are markedly larger, yet have the smallest breeding ranges near highly productive coastal upwelling systems. Short-tailed albatrosses, however, have 60% higher wing loading (weight per area of lift) compared to waved albatrosses. Indeed, calculated aerodynamic performance of waved albatrosses, the only tropical albatross species, is more similar to those of their smaller congeners (black-footed P. nigripes and Laysan P. immutabilis), which have relatively low wing loading and much larger foraging ranges that include central oceanic gyres of relatively low productivity. Globally, the aerodynamic performance of short-tailed and waved albatrosses are most anomalous for their body sizes, yet consistent with wind regimes within their breeding season foraging ranges. Our results are the first to integrate global wind and wave patterns with albatross aerodynamics, thereby identifying morphological specialization that may explain limited breeding ranges of two endangered albatross species. These results are further relevant to understanding past and potentially predicting future distributional limits of albatrosses globally, particularly with respect to climate change effects on basin-scale and regional wind fields.

Ontogenetic changes in at-sea distributions of immature short-tailed albatrosses Phoebastria albatrus

“…This may be reflected in the gradual shift of bathymetrically linked habitat preference that we observed. Previous tracking suggested that juveniles are traveling twice the distances per day that adult birds travel (Suryan et al 2008). We found seasonal differences in daily travel distances but we did not observe an ontogenetic shift in travel distance for our birds.…”

“…It is uncertain, however, why immature birds occupy regions not typically used by adults. Such differences in distribution could be driven by innate differences in the foraging capacity, aerodynamic performance between immatures and adults (Shaffer et al 2001a, Suryan et al 2008, or by timing and energetic constraints (e.g. molt, recovery from reproduction) faced by annually breeding birds that prevent them from visiting more distant seasonally productive regions (e.g.…”

Moving in a moving medium: new perspectives on flight

“…This leads to the interesting irony that while flying animals are celebrated for their ability to escape the apparent bonds of the ground, many of them exploit, and in some cases depend on [40], heterogeneity in the airscape that derives from the air's interaction with the substrate, rendering them less 'free' than we might imagine them to be. In support of this, there is increasing evidence that the distribution of a range of highly aerial species is fundamentally linked to the properties of the aerial environment [41,42]. Ultimately, the extent to which animals vary their flight paths in relation to airflows will depend on the interplay between internal and external factors (cf.…”

Quantifying habitat use and preferences of pelagic seabirds using individual movement data: a review

“…Recent research has highlighted the effects of wind on the energetic and temporal costs incurred by seabirds during flight (Weimerskirch et al 2000, Suryan et al 2008. Flight performance is partly dependent on wing loading, leading to suggestions that birds with higher wing loadings are better adapted to windier areas (Shaffer et al 2001, Suryan et al 2008.…”

“…Flight performance is partly dependent on wing loading, leading to suggestions that birds with higher wing loadings are better adapted to windier areas (Shaffer et al 2001, Suryan et al 2008. Migrating and breeding Procellariiformes route their journeys and make behavioral decisions so as to exploit favorable winds at fine to mega-scales (Murray et al 2003, Felicisimo et al 2008).…”