Avian Conservation Practices Strengthen Ecosystem Services in California Vineyards

Abstract

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.

Quantifying pest control services by birds and ants in Kenyan coffee farms

“…Arthropod variables included total abundance, diversity and average size. with regards to agriculture, has gained increasing awareness (Daily 1997, Bianchi et al 2006, Sekercioglu 2006, Van Bael et al 2008, Jedlicka et al 2011, Wenny et al 2011, Tscharntke et al 2012. Ecosystem services are defined broadly as the benefits people obtain from ecosystems and are divided into four categories: cultural, provisioning, supporting, and regulating (MEA 2005).…”

“…Birds are highly mobile and, with over 50% of all species primarily insectivorous, are ideal providers of pest control services (Wenny et al 2011). Birds have been shown to decrease insects in a variety of systems (Bock et al 1992, Mols and Visser 2002, Kellermann et al 2008, Jedlicka et al 2011, Karp et al 2013. Furthermore, studies have shown that birds not only reduce pest populations, but that plants respond with higher levels of productivity (Whelan et al 2008, Mooney et al 2010.…”

“…There is strong evidence that bird population characteristics, such as diversity and composition, affect the provisioning of these services. Studies have shown that bird species richness (Perfecto et al 2004, Van Bael et al 2008, bird density (Perfecto et al 2004), functional richness (Philpott et al 2009), both species richness and predator abundance (Jedlicka et al 2011), and the presence of migratory species (Van Bael et al 2008) are all positively correlated with the top-down control of pests. Bird species richness and bird density are often intertwined, with diversity increasing with observed abundance (Perfecto et al 2004).…”

“…While the relationships between biodiversity and level of intensification, as well as between bird and ant communities and pest control services are well documented (Vandermeer et al 2002, Armbrecht and Perfecto 2003, Perfecto et al 2004, Van Bael et al 2008, Philpott et al 2009, Jedlicka et al 2011, only a few studies have examined the direct effects of farm and landscape variables on pest predation. In the few studies examining direct effects, pest control was positively associated with measures of vegetation complexity Armbrecht 2006, Armbrecht andGallego 2007), had no relationship with measures of vegetation (Kellermann et al 2008, Philpott et al 2009 or was actually negatively correlated with vegetation complexity, potentially due to higher ambient levels of pests in sun coffee (Johnson et al 2010).…”

“…Therefore, I performed a sentinel pest experiment to simulate elevated levels of a novel insect pest and examined the predictions outlined above. In the literature, sentinel pest experiments are commonly used to compare relative predation pressure under varying conditions and have been used to relate predation rates to bird populations and distributions (Jedlicka et al 2011) and to structural diversity (Perfecto et al 2004). …”