Citizen science data reveal altitudinal movement and seasonal ecosystem use by hummingbirds in the Andes Mountains

Ensuring connectivity is crucial to protect landscapes but it requires
knowledge about how animals use ecosystems throughout the year. However,
animal movements remain largely unknown in biodiversity hotspots, even for
species that fulfill key ecological roles, as is the case of hummingbirds
in the Andes. In the complex topography of mountain slopes, movement of
these avian pollinators may occur either between habitat patches with
asynchronous plant blooms or across ecosystems that are located within
same elevation bands or along altitudinal gradients. Here, we used two
decades (2000-2020) of records from citizen science data and boosted
regression trees to predict monthly distributions for 55 hummingbird
species in the Andes. We identified shifts in altitudinal distribution
between contiguous months and calculated changes in the proportion of
predicted distributions occupied by ecosystem types. Our findings reveal
substantial altitudinal movement and differences in the proportion of
ecosystem types utilized throughout the year that had not been previously
reported for several species. Yet the magnitude of altitudinal and
ecosystem shifts varies between hummingbird clades, and in some cases
changes in the proportion of ecosystem types within estimated
distributions occurs with little variation in altitude. All ecosystems
across the Andes show temporal changes in hummingbird occurrence, but
these are higher in natural landscapes compared to croplands or urban
areas. Finally, we used phylogenetic logistic regression to test whether
altitudinal and ecosystem shifts affect population trends. We found that
higher ecosystem seasonality is more strongly associated with decreasing
populations in comparison to altitudinal shifts. Altogether, our study
reveals complex patterns of movement in hummingbirds and highlights the
importance of ecological connectivity across different ecosystem types.
More generally, it demonstrates the opportunity of using citizen science
data to increase understanding about species’ seasonal occurrences so that
landscapes can be better managed to protect animal movement.