Partial migration is a phenomenon where migratory and resident individuals of the same species co-exist within a population, and has been linked to both intrinsic (e.g., genetic) as well as environmental factors. Here we investigated the genomic architecture of partial migration in the Common blackbird, a songbird that comprises resident populations in the southern distribution range, partial migratory populations in central Europe and exclusively migratory populations in northern and eastern Europe. We generated whole-genome sequencing data for 60 individuals across the species’ distribution range, including resident populations (Spain and France), obligate migrants (Russia), and a partial migratory population with equal numbers of migratory and resident individuals in Germany. We estimated genetic differentiation (FST) of single-nucleotide variants (SNVs) in 2.5 kb windows between all possible population and migratory phenotype combinations, and focused our characterization on birds from the partial migratory population in Germany that have been individually phenotyped with radio-telemetry tracking. Despite overall low differentiation within the partial migratory German population, we identified several outlier regions with elevated differentiation on four distinct chromosomes. The region with the highest relative and absolute differentiation was located on chromosome 9, overlapping PER2, which has previously been shown to be involved in the control of the circadian rhythm across vertebrates. While this region showed high levels of differentiation, no fixed variant could be identified, supporting the notion that a complex phenotype such as migratory behavior is likely controlled by a large number of genetic loci.

Animals disperse the seeds of 60-90% of trees in tropical rainforests, which are among the most structurally complex ecosystems on Earth. Here, we investigated how 3D rainforest structure influences the movements of large, frugivorous birds and resulting spatial patterns of seed dispersal. We GPS-tracked white-thighed (Bycanistes albotibialis) and black-casqued hornbills (Ceratogymna atrata) in southern Cameroon and found that both species preferred areas of greater canopy height, and white-thighed hornbill preferred areas of greater vertical complexity. In addition, 33% of the hornbills preferred areas close to canopy gaps, while 16.7% and 27.8% avoided large and small gaps, respectively. White-thighed hornbills avoided swamp habitats, while black-casqued preferred them during the hottest temperatures. We mapped spatial probabilities of seed dispersal by hornbills, showing that 3D structural attributes shape this ecological process by influencing hornbill behavior. These results provide evidence of a possible feedback loop between rainforest vegetation structure and seed dispersal by animals.

Migrating animals respond to seasonal changes in the environment, and therefore they should time migration to coincide with peaks in resource abundance. However, it is unclear if and how frugivorous animals use phenological events to time migration, especially in the tropics. The straw-colored fruit bat (Eidolon helvum), Africa’s most gregarious fruit bat and a key seed disperser, forms large seasonal colonies through much of sub-Saharan Africa. We hypothesized that aggregations of straw-colored fruit bats match the timing of their migration with some landscape phenologies. Using monthly colony counts from seventeen sites across much of their range, we matched peak colony size to peaks in remote sensing measures of enhanced vegetation index (EVI), instantaneous rate of green up (IRG), precipitation (PRP), and the instantaneous rate of change of precipitation (IRP). Peak colony size was closest to peak IRG (60% of peak sizes occur within 1 month of peak IRG), while IRP was a close second. Sites with closer temporal matching by colonies typically had higher maximum EVI, high seasonal variation, or a short growing season, and larger peak colony size. E. helvum seem to time their migrations to move into highly seasonal landscapes and away from their core distributional range in the tropical forest belt to exploit short-lived explosions of food. The link between rapid changes in colony size and phenological match may also imply a potential collective sensing of the environment, which could be threatened by overall decreasing bat numbers along with various threats faced by large colonies.

Food distribution and availability fundamentally shape foraging. Yet spatiotemporal distribution of mobile prey and its proximate effects on animals have rarely been assessed. The neotropical bat, Noctilio albiventris, forages on aquatic swarming insects which peak just one to two hours after dusk. We matched seasonal insect distribution at high spatiotemporal resolution to the foraging behavior of adult female bats. Surprisingly, insect abundance was lower in the wet season, and insect patches dispersed more rapidly. Correspondingly, bats emerged 45% earlier, foraged over 40% longer, and flew almost twice as far compared to the dry season. Wet season bats also spent less time at each patch, suggesting that patches, though the same size, were less dense and depleted more rapidly. Our results highlight the tight link between foraging and sharp seasonal shifts in the spatial unpredictability and temporal ephemerality of resources, shedding light on behavioral adaptations and plasticity in response to resource fluctuation.