Patch size effects on avian foraging behaviour: implications for tropical forest restoration design.
Abstract
Active restoration to rehabilitate degraded tropical lands often involves planting tree seedlings, an effective but expensive approach if large areas are planted. Planting small patches of vegetation (tens to a few hundred square metres) has recently been suggested as a more economical restoration technique that mimics natural regeneration processes. However, few studies have examined the consequences of restoration patch size on animals, whose presence and activities are often key to successful ecosystem recovery. We examined the effects of patch size on the foraging behaviour of four resident tropical bird species in a replicated forest restoration experiment in southern Costa Rica. We also measured arthropod abundance and anti-predator vigilance behaviour to assess whether variation in food availability or predation risk could explain patch size effects on foraging behaviour. Prey attack rates were highest, and the effort required to find prey was lowest, in larger patches for three of the four bird species. Arthropod density was approximately twice as great in larger patches (>3500 m2) compared with smaller patches (<350 m2). Evidence for patch size differences in predation risk was more limited but risk may be higher in smaller patches. The results indicate that food availability is the primary mechanism driving patch size effects on foraging behaviour, with predation risk being an additional influence for some species in some years. Synthesis and applications. As demonstrated in this study, patches of tens to a few hundreds of metres squared are likely to provide fewer food resources and potentially less cover from predators for vertebrates that use woody habitat, compared with patches of a few thousand square metres. The more limited resources in smaller patches are likely to have short-term and, potentially, long-term consequences for the fitness of organisms. When considering restoration project design, the potential economic and other benefits of planting in smaller patches must be weighed with the potentially negative ecological effects on some taxonomic groups. To increase the probability that patches provide adequate habitat for the largest number of species, we recommend that when financial resources are available, patches of at least a few thousand square metres be planted.