Large birds travel farther in homogeneous environments

Aim: Animal movement is an important determinant of individual survival, population dynamics, and ecosystem structure and function. Yet it is still unclear how local movements are related to resource availability and the spatial arrangement of resources. Using resident bird species and migratory bird species outside of the migratory period, we examined how the distribution of resources affect the movement patterns of both large terrestrial birds (e.g., raptors, bustards, hornbills) and waterbirds (e.g., cranes, storks, ducks, geese, flamingos). Location: Global Time Period: 2003 - 2015 Major taxa studied: Birds Methods: We compiled GPS tracking data for 386 individuals across 36 bird species. We calculated the straight-line distance between GPS locations of each individual at the 1-hour and 10-day timescales. For each individual and timescale, we calculated the median and 0.95 quantile of displacement. We used linear mixed-effects models to examine the effect of the spatial arrangement of resources, measured as Enhanced Vegetation Index (EVI) homogeneity, on avian movements while accounting for mean resource availability, body mass, diet, flight type, migratory status and taxonomy and spatial autocorrelation. Results: We found a significant effect of resource spatial arrangement at the 1-hour and 10-day timescales. On average, individual movements were seven times longer in environments with homogeneously distributed resources compared with areas of low resource homogeneity. Contrary to previous work, we found no significant effect of resource availability, diet, flight type, migratory status or body mass on the non-migratory movements of birds. Main conclusions: We suggest that longer movements in homogeneous environments may reflect the need for different habitat types associated with foraging and reproduction. This highlights the importance of landscape complementarity, where habitat patches within a landscape include a range of different, yet complimentary resources. As habitat homogenisation increases, it may force birds to travel increasingly longer distances to meet their diverse needs.