Riverine Barriers as Obstacles to Dispersal in Amazonian Birds

Abstract

Amazonian rivers represent known barriers for avian dispersal, reducing gene flow and enhancing differentiation. Despite the importance of rivers in the avian evolutionary process, we have made only minor advances in understanding the limitations imposed by rivers on flying birds. To fill that gap, we conducted dispersal-challenge experiments over water, assessing the flying capabilities of 84 tropical bird species of 22 different avian families. We mist-netted and released 484 birds from a stationary boat on the Rio Branco, northern Amazonia, at increasing distances from the shore, including 249 individuals at 100; 219 at 200; 8 at 300; and 5 at 400 m. A successful trial was represented by a bird reaching the riverbank, whereas a failure would refer to birds not reaching the shore and landing on the water, when they were rescued by our team. Our main goal was to understand if the outcome in the experiments could be predicted by (i) phylogenetic constraints, (ii) morphology (body mass and wing shape), (iii) flight speed, (iv) ecological preferences (stratum, habitat, and river-island specialization), and (v) psychological reluctance to fly. Nearly two thirds of the individuals (332) were successful in reaching the riverbank, whereas 152 failed. We found significant differences among lineages. Whereas seven avian families succeeded in all of the trials, two families (antbirds and wrens) were particularly bad dispersers (<40% success). The hand-wing index (HWI) was the single most powerful predictor of trial success. Flying speed was also a significant predictor of success. Overall, ecological attributes had a low explanatory power. Only forest stratum preference had a significant, although weak, effect on dispersal ability: canopy- and ground-dwellers performed better than understory birds. However, we found no effect of habitat preference or river-island specialization on dispersal ability. Our speed estimates for 64 bird species are among the first produced for the tropics and suggest slower flying speeds than those reported from temperate migratory birds. Although birds showed behavioral differences when presented with the opportunity to fly away from the boat, we found no evidence that their reluctance to fly could predict the outcome in the experiments. This represents the first experimental study evaluating the riverine effect through dispersal ability of Amazonian birds, providing important insights to better understand dispersal limitations provided by riverine barriers.

Amazonian birds in more dynamic habitats have less population genetic structure and higher gene flow

“…This metric is typically based either on morphology, such as wing shape (Claramunt, 2021; Kipp, 1959), or on ecological traits thought to predispose species to dispersive lifestyles, such as foraging ecology and diet (Burney & Brumfield, 2009; Miller et al, 2021). Recently, researchers have also conducted dispersal challenge experiments to measure an individual's relative flying ability (Moore et al, 2008; Naka et al, 2022). Naka et al (2022) found no correlation in these experiments between flight distance and riverine island specialization, suggesting that wing shape, rather than ecological preference, better explains the capacity of birds to cross an open gap of water.…”

“…The Amazon Basin has high avian species richness (Jenkins et al, 2013; Wallace, 1878), long‐term evolutionary persistence (Bicudo et al, 2019; Harvey et al, 2017b), a wide diversity of habitat types (Tuomisto et al, 1995; Tuomisto et al, 2019), and species with a diversity of habitat preferences and specializations (e.g., Álvarez Alonso et al, 2013; Kratter, 1997; Rosenberg, 1990; Terborgh, 1985). Additionally, experimental dispersal challenges over water are now available for some Neotropical birds (Moore et al, 2008; Naka et al, 2022). Claramunt et al (2022) found that wing morphology was a significant predictor of overwater flight ability and Weeks et al (2022) found a significant association between flight ability and natal dispersal distance in a phylogenetically diverse set of 114 bird species, supporting wing measurements from research specimens as a proxy for dispersal.…”

Late Pleistocene landscape changes and habitat specialization as promoters of population genomic divergence in Amazonian floodplain birds

“…Data on dispersal capacity, however, indicate that C. bicolor is a better disperser than both M. propinqua and S. napensis (Naka et al, 2022). In dispersal challenge experiments conducted on the Rio Branco, C. bicolorcolour managed to safely cross river gaps in all trials (10:0), whereas S. napensis failed in 25% and M. propinqua in more than 50% of the trials.…”

Determinants of natal dispersal distances in North American birds

“…In these habitats, species need larger foraging areas and thus enhanced mobility in order to obtain sufficient resources. Finally, even in productive tropical forests, ground‐foraging species may show higher levels of mobility than species that forage on understory vegetation (Claramunt et al, 2022 ; Naka et al, 2022 ). These factors may complicate the relationship between foraging behavior and dispersal distances.…”

“…Because of its role in determining the efficiency of movements through space, flight efficiency can also influence other aspects of birds' biology. For example, flight efficiency has a strong influence on the species' ability to cross habitat gaps and move across fragmented landscapes (Claramunt et al, 2012(Claramunt et al, , 2022Hartfelder et al, 2020;Ibarra-Macias et al, 2011;Naka et al, 2022). Flight efficiency may also be linked to foraging behavior and, by extension, to diet and habitat (Norberg, 1990;Rayner, 1988;Sherry, 2016).…”