Multi-scale responses of forest-dependent Neotropical birds to landscape gradients

Background/Question/Methods

Understanding habitat requirements for target species is required to optimize conservation planning. However, most research uses a limited number of spatial extents, defined by a-priori hypotheses. Since scale-specific responses are not well understood for many species, studies that fail to consider a wider range of scales can miss important relationships. Many reforestation initiatives in Costa Rica aim to benefit forest birds by reducing historic fragmentation. While many understory insectivorous birds are sensitive to fragmentation, responses in other feeding guilds are less documented. We hypothesized that diet and foraging stratum would drive habitat use patterns, and expected frugivorous and canopy species to respond positively to edge density at finer scales, unlike insectivorous and understory species, since fruit is abundant along the forest edge and the canopy contains greater structural heterogeneity. We collected avian abundance data using 10-minute dependent double-observer point counts at 301 randomly stratified sites reflecting key landscape gradients in northwestern Costa Rica from May - December, 2016 - 2018. We then constructed hierarchical multinomial N-mixture models for 18 commonly detected species. Models contained single landscape gradients (e.g., edge density) calculated for 10 focal extents (100 – 1000 m) around each site to compare species’ responses across a range of scales.

Results/Conclusions

While responses of individual species to landscape gradients across scales varied, general patterns supported hypotheses. Canopy and frugivorous species responded more positively to increases in edge density at fine scales than understory and insectivorous species, but edge density negatively affected abundance of all species at broader scales. For example, edge density most positively affected abundance in the frugivorous Long-tailed Mankin (Chiroxiphia linearis) at the 200 m scale (0.4±0.02 individuals per 10 meters/hectare increase), but negatively affected abundance at scales >500 m (-0.07±0.01), while the understory-dwelling, insectivorous Rufous-and-white Wren (Thryophilus rufalbus) negatively responded to edge density at all scales (100 m: -1.16 ± 0.04; 1000 m: -1.19 ± 0.05). Effective reforestation plans must balance not only the needs of multiple species, but also habitat requirements of single species at multiple scales. For example, strategies such as windbreaks may support local foraging in frugivorous and canopy species, but will not support species’ persistence, since interior forest is required at broader scales to provide protection from predators and inconspicuous nesting sites. This tradeoff would be missed if a wide range of focal scales was not considered. This research highlights the necessity of multi-scale approaches to inform conservation planning.