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.
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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)