Management effect on bird and arthropod interaction in suburban woodlands

Erik Heyman,Bengt Gunnarsson

doi:10.1186/1472-6785-11-8

Abstract

BackgroundExperiments from a range of ecosystems have shown that insectivorous birds are important in controlling the populations of their invertebrate prey. Here, we report on a large field experiment testing the hypothesis that management for enhancing recreational values in suburban woodlands affects the intensity of bird predation on canopy-living arthropods. Bird exclosures were used in two types of management (understory clearance and dense understory) at two foraging heights in oak Quercus robur canopies and the experiment was replicated at two sites.ResultsThe biomass and abundance of arthropods were high on net-enclosed branches but strongly reduced on control branches in both types of management. In woods with dense understory, the effect of bird predation on arthropod abundance was about twice as high as in woods with understory clearance. The effect of bird predation on arthropod biomass was not significantly affected by management.ConclusionsOur data provide experimental evidence to support the idea that bird predation on arthropods can be affected by forest management. We suggest that the mechanism is twofold: reduction of bird abundance and shift of foraging behaviour. In urban woodlands, there may be a management trade-off between enhancing recreational values and promoting bird predation rates on arthropods.

Highlights

Experiments from a range of ecosystems have shown that insectivorous birds are important in controlling the populations of their invertebrate prey
In a large-scale, replicated field experiment, we examined effects of forest management on bird predation pressure on arthropods
Effects of the bird exclosures across sites, management types and height levels were found to be strong for both arthropod abundance (t = -3.441, df = 87, p = 0.001) and biomass (t = -7.356, df = 87, p < 0.001)

Summary

Introduction

Experiments from a range of ecosystems have shown that insectivorous birds are important in controlling the populations of their invertebrate prey. Avian insectivores reduce arthropod abundances in winter [16,26], as well as in summer [27,28], and reduce the mean size of arthropods in both managed coniferous forests [27] and deciduous stands in city parks and suburban woodlands [28]. Taken together these studies provide substantial evidence that avian predators contribute to controlling arthropod abundances in forests of southern Sweden. We anticipated that birds in our experiment would affect their arthropod prey in a similar way

Methods

Results

Discussion

Conclusion