The future of food production relies on minimising negative environmental impacts and maximising the ecosystem services (ES) that nature provides to agriculture. Birds foraging in agroecosystems can have both positive and negative impacts on annual production;however, few studies address the cost-benefit trade-offs of these activities. I conducted a systematic review of the costs and benefits of bird activity in agroecosystems (Chapter 2) and found that most birds studied were omnivores, with a clear geographic bias towards studies on bird damage to crops (costs) in North America and studies on ES provided by birds (benefits) in Central America/Caribbean. I then used three case studies to examine cost-benefit trade-offs of bird activity in apple orchards, pastoral systems and vineyards in south-eastern Australia. In Chapter 3, I calculated the net outcome of bird feeding activity for fruit production in apple orchards. When trading off potential benefits (biological control of insect pests) with costs (bird damage to apples), I found that birds provided an overall net benefit to orchard growers: an increase in yield of 10.9%. This benefit increased with decreasing management intensity; therefore, providing suitable habitat for insectivorous bird species in close proximity to orchards may improve the biological control of apple pests. In Chapter 4, I determined the role of avian scavengers in removing rabbit carcasses in pastoral landscapes by comparing the percent weight loss of bird accessible carcasses with bird inaccessible carcasses. Bird accessible carcasses had the highest percent weight loss, mostly due to the activity of raptors which removed a median of 16.17% of the carcasses they attacked. Raptors are likely major contributors to carcass disposal in pastoral landscapes and maintaining key habitat features for these species (e.g. large paddock trees) is essential for raptor conservation and maximising the ES they provide. In Chapter 5, I tested the effect of providing artificial perches for encouraging predatory birds into vineyards to scare grape-eating birds and subsequently reduce the damage they cause to grapes. The aggressive Australian magpie (Cracticus tibicen) was the most common visitor to perches. Artificial perch sites recorded 50% less grape damage (4.13% damage per bunch) than control sites without perches (8.57% damage per bunch), suggesting that providing artificial perches in vineyards may help reduce bird damage to grapes. Finally, in Chapter 6, I determined if bird functional trait diversity and/or environmental variables had an influence on the costs or benefits of bird activity in agroecosystems. Percent tree cover and the distance of a site to unmanaged vegetation were in some circumstances useful in predicting response trait functional richness of birds. In pastoral landscapes, response trait functional richness of scavenging birds increased with less tree cover. This suggests, for example, that scavenging bird communities in open fields had a greater diversity of response traits and therefore the community has greater capacity to adapt to changes in environmental conditions. The distance of a site to unmanaged vegetation and effect trait functional divergence of birds were in some cases useful in predicting the delivery of an ESor disservice. In vineyards, sites that were closer to native vegetation appeared to receive less grape damage, and in pastoral landscapes, having extremes of scavenging bird effect traits at a site appeared to increase bird removal of carcasses. These results highlight the importance of including both environmental variables and functional traits in examining bird relationships with ecosystem function. Overall, my thesis shows that comparing both benefits and costs when researching fauna activity in agroecosystems is important for the future sustainability of agriculture.
|Qualification||Doctor of Philosophy|
|Award date||01 Aug 2017|
|Publication status||Published - 2017|