Movement strategies of neotropical nectarivorous birds: Insights from high-Andean hummingbirds and flowerpiercers

Tropical nectarivorous birds should have flexible movement behaviors in
response to the spatiotemporal availability of flowers. In the Neotropics,
hummingbirds (Trochilidae) have diet breadths constrained by
trait-matching with flowers, while nectar-robbing flowerpiercers
(Thraupidae) typically drink nectar from holes pierced at the flower’s
base. Distinct movement patterns for these two bird families would be
expected from optimal foraging theory due to differences in dietary
specialization and behavioral flexibility, yet little is known about the
daily movement patterns of tropical nectarivores. We used fine-resolution
tracking data from an automated radio telemetry grid to compare movement
patterns between hummingbirds and flowerpiercers in high-Andean mountain
ecosystems, and obtained an accumulated total of 435,513 location
estimates and 452 tracking days from 22 individuals across six bird
species. Our results indicate that hummingbirds exhibit a greater
diversity of movement behaviors compared to flowerpiercers, with varying
space use and recursion patterns that are characteristic of sedentary,
commuting/traplining, and exploratory strategies, whereas most species of
flowerpiercers were classified as central-place foragers. However, there
is substantial variation in daily movement metrics and hierarchical
clustering does not necessarily group together bird families, species, nor
even individuals as more similar to each other. Flexibility in movement
behaviors has seldom been described for neotropical nectarivorous birds in
the wild. It emerges as an important trait to adjust behavior to variable
local contexts, and may be adaptive for the persistence of pollinators in
challenging mountain ecosystems, where weather conditions are harsh and
floral resources are seasonal.