Patch size effects on avian foraging behaviour: implications for tropical forest restoration design

Abstract

Summary1. 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. 2. 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. 3. 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 m 2 ) compared with smaller patches (<350 m 2 ). 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. 4. 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, longterm 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.

Bird Pollinator Visitation is Equivalent in Island and Plantation Planting Designs in Tropical Forest Restoration Sites

“…Unlike our previous work indicating that insectivorous and frugivorous birds used plantation-style treatments more than island treatments [10,11,33], planting treatment did not influence numbers of pollinator bird visits to trees in islands compared to plantations. The number of pollinator visits to I. edulis was driven primarily by conspecific flower density in focal trees e.g., [20,21].…”

“…While a focus on particular species may be warranted in some cases [17], restoring ecological processes will often be a more constructive and attainable goal. This work indicates that pollination in the early years following planting may not be as affected by characteristics of restoration design as other ecological processes like seed dispersal and vertebrate consumption of herbivorous arthropods e.g., [10,11]. Future work to assess whether our results extend to other plantpollinator interactions, which potential pollinator species of I. edulis are the most effective pollinators, and their specific responses to restoration design, will be important in assessing this idea.…”

“…Thus, although plantation-style planting likely has a positive influence on the ecological processes of arthropod reduction by vertebrates and seed dispersal, through positive effects on insectivorous and frugivorous birds [10,11,33], similar effects may not occur for pollination, at least at this stage of forest recovery. These findings are in accord with recent work showing that different species interaction networks within ecosystems will not necessarily respond similarly to restoration strategies [36].…”

“…If island planting facilitates restoration equally as well as plantation-style planting, it would be preferred because of lower costs [9]. Our previous work in southern Costa Rica has shown that plantation-style plantings are used more extensively by both insectivorous and frugivorous birds than island plantings, with potential consequences for the ecological processes of arthropod reduction and seed dispersal [10,11].…”

Why are woodland-dependent avian insectivore populations vulnerable to declines in highly-modified landscapes?

“…However, this idea runs counter to many invertebrate studies that find mixed results of landscape structure on invertebrate abundance and richness with taxonomic groups showing idiosyncratic responses to habitat loss and fragmentation (Helle & Muona 1985;Van Wilgenburg et al 2001;Laurance et al 2011;Moreno et al 2013). In reality, few studies have directly measured prey availability for avian insectivores and results have been mixed with prey showing either negative relationships (Burke & Nol 1998;Zanette et al 2000;Luck 2003;Morrison et al 2010) or no relationship (Şekercioğlu et al 2002;Butcher et al 2010) to measures of habitat loss or fragmentation. To compound the problem, some of these studies have limited replication at the level of habitat patch or landscape Şekercioğlu et al 2002;Luck 2003).…”