Abstract
An organism’s ability to disperse influences many fundamental processes, from speciation and geographical range expansion to community assembly. However, the patterns and underlying drivers of variation in dispersal across species remain unclear, partly because standardised estimates of dispersal ability are rarely available. Here we present a global dataset of avian hand-wing index (HWI), an estimate of wing shape widely adopted as a proxy for dispersal ability in birds. We show that HWI is correlated with geography and ecology across 10,338 (>99%) species, increasing at higher latitudes and with migration, and decreasing with territoriality. After controlling for these effects, the strongest predictor of HWI is temperature variability (seasonality), with secondary effects of diet and habitat type. Finally, we also show that HWI is a strong predictor of geographical range size. Our analyses reveal a prominent latitudinal gradient in HWI shaped by a combination of environmental and behavioural factors, and also provide a global index of avian dispersal ability for use in community ecology, macroecology, and macroevolution.
Highlights
An organism’s ability to disperse influences many fundamental processes, from speciation and geographical range expansion to community assembly
These spatial patterns are largely recapitulated in both non-passerines and passerines, the latitudinal gradient is shallower in passerines with relatively high hand-wing index (HWI) much more broadly distributed across the temperate zone, in the northern hemisphere
In contrast with range size models, there are differences in secondary predictors of migration between non-passerines and passerines, including factors such as diet, climate and hemisphere (Supplementary Tables 8 and 9). These findings confirm that HWI predicts migration, but it is difficult to infer underlying mechanisms because wing morphology could be the cause or consequence of long-distance movement – our results suggest that a combination of these effects explains relatively tight co-evolution between HWI and migration reported in previous studies[25,28,33,44]
Summary
An organism’s ability to disperse influences many fundamental processes, from speciation and geographical range expansion to community assembly. We present a global dataset of avian hand-wing index (HWI), an estimate of wing shape widely adopted as a proxy for dispersal ability in birds. Our analyses reveal a prominent latitudinal gradient in HWI shaped by a combination of environmental and behavioural factors, and provide a global index of avian dispersal ability for use in community ecology, macroecology, and macroevolution. Natal and breeding dispersal data were made available for 75 British bird species based on nearly 100 years of intensive mark-recapture data[22], while a recent survey of mammalian movement was based on GPS data from only 57 species[27] Until such measurements become easier to implement at a wide scale, the most promising approach for comparative analyses relies on standardised biometric indices of dispersal. Birds – the largest tetrapod radiation – provide an ideal test case for a broad-scale analysis of dispersal morphology because they are globally distributed and reasonably well studied, with a full species-level phylogeny[37] and complementary datasets on geographical distribution, along with a range of ecological, behavioural and other life history variables[38,39,40]
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