Forest-dependent Neotropical bird species can be adversely affected by forest fragmentation, which decreases habitat area and connectivity, restricting access to mates and food and increasing competition. Declines of understory insectivores in fragmented Neotropical landscapes have been highlighted in many studies, but few have examined effects on other feeding guilds. Species of different guilds likely respond to fragmentation at different spatial scales due to differences in life histories. We hypothesize that understory frugivores, canopy frugivores, and understory nectarivores will respond positively to forest fragmentation at fine scales, since food sources (i.e., flowering and fruiting plants) are often abundant along forest edges, but negatively at coarser scales, as forest nesting area decreases. In a fragmented landscape in northwestern Costa Rica, we collected occupancy data using 10 minute dependent double observer point counts at randomly selected sites within 10 zones designed to capture major landscape gradients (e.g., elevation, mean patch size). We conducted point counts at 287 sites from May – December 2016 and 2017, recording 10,176 individuals representing 280 species. Species were grouped into 15 feeding guilds based on diet and foraging stratum. Logistic models were used to determine how landscape gradients were related to bird presence by guild at multiple spatial scales.
Results/Conclusions
We selected three focal feeding guilds to describe the effects of forest fragmentation at multiple scales on forest-dependent bird guilds: canopy frugivores (CF), understory frugivores (UF), and understory nectarivores (UN). At fine scales, CFs displayed negative relationships with mean forest patch size (coefficient: -0.019), as did UNs (-0.013), while UFs had a positive relationship (0.262), but all three focal guilds displayed positive relationships with mean forest patch size at coarser scales (CF: 0.343, UF: 0.296, UN: 0.188). These guilds also displayed positive relationships with percent forest cover at coarser scales (CF: 0.493, UF: 0.417, UN: 0.28), but CFs showed a negative relationship at finer scales (-0.144). Thus, for CFs and UNs, local disturbances, such as small subsistence farms and shade grown coffee that leave sizeable forested areas intact will likely allow many species to persist, while more intensive human land uses, such as large scale agriculture or urban development, likely will not. UFs appear to occur in areas of larger forest patches at all scales, and thus may benefit the most from targeted afforestation/reforestation efforts. Results from this study will be used to help local conservation organizations develop priorities for land management efforts and reforestation initiatives.