Avian Conservation Practices Strengthen Ecosystem Services in California Vineyards

PLOS ONE, Nov 2011

Insectivorous Western Bluebirds (Sialia mexicana) occupy vineyard nest boxes established by California winegrape growers who want to encourage avian conservation. Experimentally, the provision of available nest sites serves as an alternative to exclosure methods for isolating the potential ecosystem services provided by foraging birds. We compared the abundance and species richness of avian foragers and removal rates of sentinel prey in treatments with songbird nest boxes and controls without nest boxes. The average species richness of avian insectivores increased by over 50 percent compared to controls. Insectivorous bird density nearly quadrupled, primarily due to a tenfold increase in Western Bluebird abundance. In contrast, there was no significant difference in the abundance of omnivorous or granivorous bird species some of which opportunistically forage on grapes. In a sentinel prey experiment, 2.4 times more live beet armyworms (Spodoptera exigua) were removed in the nest box treatment than in the control. As an estimate of the maximum foraging services provided by insectivorous birds, we found that larval removal rates measured immediately below occupied boxes averaged 3.5 times greater than in the control. Consequently the presence of Western Bluebirds in vineyard nest boxes strengthened ecosystem services to winegrape growers, illustrating a benefit of agroecological conservation practices. Predator addition and sentinel prey experiments lack some disadvantages of predator exclusion experiments and were robust methodologies for detecting ecosystem services.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0027347&type=printable

Avian Conservation Practices Strengthen Ecosystem Services in California Vineyards

Citation: Jedlicka JA, Greenberg R, Letourneau DK ( Avian Conservation Practices Strengthen Ecosystem Services in California Vineyards Julie A. Jedlicka 0 1 Russell Greenberg 0 1 Deborah K. Letourneau 0 1 Adina Maya Merenlender, University of California, Berkeley, United States of America 0 Current address: Department of Environmental Science , Policy and Management , University of California , Berkeley, California , United States of America 1 1 Department of Environmental Studies, University of California Santa Cruz, Santa Cruz, California, United States of America, 2 Migratory Bird Center, Smithsonian Conservation Biology Institute , National Zoological Park, Washington, DC , United States of America Insectivorous Western Bluebirds (Sialia mexicana) occupy vineyard nest boxes established by California winegrape growers who want to encourage avian conservation. Experimentally, the provision of available nest sites serves as an alternative to exclosure methods for isolating the potential ecosystem services provided by foraging birds. We compared the abundance and species richness of avian foragers and removal rates of sentinel prey in treatments with songbird nest boxes and controls without nest boxes. The average species richness of avian insectivores increased by over 50 percent compared to controls. Insectivorous bird density nearly quadrupled, primarily due to a tenfold increase in Western Bluebird abundance. In contrast, there was no significant difference in the abundance of omnivorous or granivorous bird species some of which opportunistically forage on grapes. In a sentinel prey experiment, 2.4 times more live beet armyworms (Spodoptera exigua) were removed in the nest box treatment than in the control. As an estimate of the maximum foraging services provided by insectivorous birds, we found that larval removal rates measured immediately below occupied boxes averaged 3.5 times greater than in the control. Consequently the presence of Western Bluebirds in vineyard nest boxes strengthened ecosystem services to winegrape growers, illustrating a benefit of agroecological conservation practices. Predator addition and sentinel prey experiments lack some disadvantages of predator exclusion experiments and were robust methodologies for detecting ecosystem services. - Funding: Funding for this research was provided by: The Organic Farming Research Foundation (http://ofrf.org); Animal Behavior Society (http:// animalbehaviorsociety.org); Wilson Ornithological Society (http://www.wilsonsociety.org); Smithsonian Migratory Bird Center (http://nationalzoo.si.edu/scbi/ migratorybirds/default.cfm); Annies Sustainable Agriculture Graduate Scholarship (http://www.annies.com/sustainable_agriculture_scholarship); and the Environmental Studies Department at University of California Santa Cruz (http://envs.ucsc.edu). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Ecosystem services such as pest control and pollination are functions provided by biological diversity that are critical to human societies and their agricultural production [1,2]. Nevertheless, agriculture often generates environmental pollution, contributes to habitat loss and, hence, decreases biodiversity [3,4]. Environmentally sustainable farming practices are designed to foster biodiversity and ecosystem services. For example, bird-friendlyH coffee systems are well-known for their conservation value, particularly in providing habitat for insectivorous migrant bird species [5,6]. Studies comparing insect herbivore abundance with and without net caging over plants (exclosures) suggest that insectivorous birds significantly reduce both herbivorous arthropod abundance and plant damage in agricultural and natural systems [7,8]. As a result, conservation of birds in agricultural landscapes may benefit growers through the provision of pest control services. For example, outside exclosures avian predation of insect pests increased quantities of marketable fruit and raised farmer income in apple [9,10] and coffee [11,12] production systems. Experimental methods for quantifying ecosystem services are fraught with complications, because in situ manipulations (e.g. predator exclosures) can have hidden or confounding effects [13]. An alternative methodology to quantify avian predation in agroecosystems combines the manipulation of specific predator populations via the establishment of nest boxes with a sentinel prey experiment that controls for density dependent population effects. Sentinel prey studies, which monitor removal rates of immobilized, tethered, or frozen prey in the field are common in the entomology literature for comparing relative predation pressure under different conditions e.g. [14,15,16]. Often sentinel prey experiments are used in concert with predator abundance data to test the e (...truncated)


This is a preview of a remote PDF: http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0027347&type=printable

Julie A. Jedlicka, Russell Greenberg, Deborah K. Letourneau. Avian Conservation Practices Strengthen Ecosystem Services in California Vineyards, PLOS ONE, 2011, 11, DOI: 10.1371/journal.pone.0027347