- Agronomic: oats, rye, grass (misc. perennial), hay
- Fruits: berries (strawberries), melons
- Vegetables: beans, broccoli, cabbages, carrots, cucurbits, eggplant, greens (leafy), onions, peas (culinary), peppers
- Additional Plants: trees
- Animal Production: feed/forage
- Crop Production: windbreaks
- Education and Training: display, extension, on-farm/ranch research
- Farm Business Management: whole farm planning
- Natural Resources/Environment: biodiversity, hedgerows, hedges - woody, indicators, wildlife
- Pest Management: biological control
- Production Systems: agroecosystems, holistic management
- Sustainable Communities: public participation
We investigated reproduction and pest consumption by Eastern Bluebirds (Sialia sialis) on farms and natural open lands. Findings suggest that farms provide suboptimal but useful habitat for breeding bluebirds. Farmland bluebirds laid more eggs and raised more clutches than natural land bluebirds in 2007, yet birds from all treatments produced similar numbers of nestlings. In 2008, farmland bluebirds produced nearly half the number of nestlings in the first clutch than bluebirds on natural lands. Therefore, reproductive success did not differ but reproductive effort was higher on farms. Preliminary results concerning pest consumption suggest that breeding pairs on reduced-impact farms consume 76 to174 arthropods per day when feeding nestlings; the most frequent prey types included grasshoppers, crickets, and larvae (Lepidoptera, Coleoptera).
Tables, figures or graphs mentioned in this report are on file in the Southern SARE office.
Contact Sue Blum at firstname.lastname@example.org for a hard copy.
A variety of reasons have been discussed supporting efforts to increase birdlife on farms. Most farmers seem to appreciate birds (e.g., Jacobson et al. 2003), government and consumers are pushing for biodiversity-friendly produce, farmlands are increasingly replacing natural habitat, and many birds consume pest insects and could aid in biological control programs. However, scientists cannot responsibly encourage farmers to attract pest-eating songbirds to their lands without first answering two questions with more certainty. What are the realized economic benefits to farmers of encouraging wild birds to inhabit farmlands, and how suitable are farms as habitat for wild bird species? If pest-eating birds have negligible effects on pest populations or crop yield, or farms serve as ecological traps for birds, then the value to growers and society of encouraging bird-friendly agroecosystems should be vigorously questioned.
The purpose of this project is to address aspects of both questions in a farmland-bird system in North-central Florida. We provide information concerning the pest-eating potential of native insectivorous birds in organic (reduced-impact) vegetables, while also describing the reproductive success of these birds on a selection of organic and conventional farms and natural open lands. We were encouraged to conduct this work because organic farmers are facing new biodiversity guidelines from USDA/NOP stipulating that they not only protect, but actually enhance, native species on their farms (Wild Farm Alliance 2005). Therefore, in the trend toward ecological agriculture, organic producers must accommodate increasingly complex ecological interactions in systems that are already more complex than conventional systems. Ideally, management of ecological interactions and biodiversity could also favor production and economic viability, thereby enhancing the efficiency of growers’ operations. With attention to both the social and ecological aspects (and potential pitfalls) of bird-friendly farming, this work focused on providing information that can be used to assess farmland biodiversity-management options involving native bird predators of pests.
CAN WILD BIRDS HELP CONTROL CROP PESTS?
Agoecosystems, especially if they are organic or sustainably-managed, can support many native taxa, from soil invertebrates, beneficial foliage insects, bees and other pollinators, lizards, to bats, birds, and other vertebrates (Hole et al. 2005). Proven techniques to foster biodiversity, collectively termed “farmscaping for biodiversity,” are nearly as diverse as the species they attract (Bugg et al. 1998). However, growers dealing with ecological complexity require increasingly simple and low-cost techniques that serve multiple functions for enhancing overall sustainability of their operations (Ferron and Deguine 2005). A technique that attracts wildlife with neutral or negative roles in the agro-system is unlikely to be selected over a technique that brings in species playing primarily beneficial roles. In order to assess the relative value of different species that could be encouraged through habitat management (i.e., to determine which species may provide useful services such as pest control), growers need explicit information about what native species do in their systems.
Part of the underlying rationale for research reported here relates to the need for further assessment of how and when native insectivorous birds can help control invertebrate herbivore populations in agro-ecosystems. Strong (experiment-based) evidence is emerging in support of this idea from various systems, especially those dominated by woody plants. Experiments that exclude birds from access to foliage have documented that birds reduce pest numbers and increase growth of trees (Marquis and Whelan 1995), coffee plants (Greenberg et al. 2000), apple trees (Mols and Visser 2002), and even broccoli (Hooks et al. 2003). Bird suppression of pests and plant damage were measurable and/or significant in these studies. The increasing empirical evidence that birds can help control herbivorous insects is supported by a great deal of theoretical literature suggesting that because birds are generalist insectivores with high mobility, they should play strong positive roles in the mitigation of pest outbreaks (Holling 1988).
In addition to their potential as pest-controllers, birds are also highly desirable forms of “biodiversity” with wide appeal and familiarity to growers and the public (Jacobson et al. 2003). Fostering native birds of conservation importance on farms may therefore count as much or more in growers’ efforts to meet biodiversity guidelines than other taxa. Still, significant misconceptions concerning the relationship between birds and farms (in general) must be overcome. To most people, the goal of attracting birds into agricultural fields with row crops may seem foolish because, either, they have found farms to be wastelands for native birds (Peterjohn 2003) or that birds are serious crop destroyers (Avery et al. 1992). Many conservationists are convinced of the former, and many growers hold the latter perception of birds. However, birds have diverse relationships with farms, crops, and pests; dependent upon the agro-ecosystem and surrounding landscape features (Tavernier and Tolomeo 2002, Jones et al. 2005). Initial research in our lab conducted on vegetable farms in North-central Florida documented that many native birds were using organic and conventional operations, and were likely to be consuming significant numbers of important pests in vegetable fields — without causing crop damage (Jones et al. 2005). In a comparative survey, insect-feeding birds were particularly diverse and abundant in fields with mixed crops, hedges along field borders, and near wooded areas. In an experimental manipulation, pest-consuming bird species were significantly more abundant and spent significantly more time hunting for pest prey in fields where strips (intercrops) of sunflowers were grown among the vegetable crops (Jones and Sieving 2006). Thus, we began this current study with many indications that birds can participate positively in food production in vegetable cropping systems in North-central Florida, and that insectivorous birds could be readily attracted to these systems. But our concerns about whether farmlands were providing high quality habitat for native birds needed to be addressed.
DO FARMS ACT AS “ECOLOGICAL TRAPS” FOR BIRDS?
Agricultural lands can be managed for both food and biodiversity production, and there is increasing pressure to do so. The US government requires organic farmers to protect biodiversity (Wild Farm Alliance 2005), and health/environmentally-conscious consumers are creating market demand for produce branded with biodiversity-friendly certifications (e.g., Smithsonian-certified bird-friendly coffee; Grankvist and Beal 2001). Finally, as global agricultural expansion is projected to replace upward of one billion hectares of natural habitat during the next fifty years, conservationists are increasingly eyeing farmlands as critical habitat to augment insufficient areas protected in reserves (Tilman et al. 2001, Fischer et al. 2008). The argument is that if agriculture can provide some use to many species and suitable habitat for a few, then it could serve as an ecological buffer around natural areas to boost their biodiversity-holding capacity (Phillips 2002).
Natural habitats and landscape mosaics that are fragmented by agriculture, however, often do not sustain healthy ecological communities. For example, various studies from different biomes document high rates of nest failure for many interior-forest obligate birds in fragments surrounded by agriculture (Rodewald and Yahner 2001a and b, Albrecht 2004, Knutson et al. 2004, Peak et al. 2004). Fragments suffer higher rates of exotic species invasion and nest predation (Tewksbury et al. 2006) and generally diminished species richness and evenness of native communities (Rodewald and Yahner 2001b). Though farmlands may create population sinks or ecological traps for forest-requiring species (e.g., Wood Thrush [Hylocichla mustelina], Fauth 2001, Zuria et al. 2007), current thinking is that they may provide suitable habitat for species that can tolerate, or that prefer, more open lands maintained for production of food or fiber. Indeed, a central focus in conservation research right now is to characterize the potential values of “wildlife-friendly farms” and farming landscapes more generally as biodiversity buffers (Daily et al. 2001). The most direct measure of habitat quality for wild species is to assess whether habitats support adequate reproductive success and production of viable recruits to breeding populations (Hall et al. 1997).
Avian reproductive success typically appears to be higher on organic and other reduced-impact (e.g., organically managed, sustainable) farms than on conventional farms (e.g., Bouvier et al. 2005, Britschgi et al. 2006, Hart et al. 2006 – but see Graham and Desgranges 1993). While this is not surprising, we still do not know in general how farmlands compare in quality to natural openlands ecosystems as wildlife habitat. The only way to do that is via comparisons of reproduction across the wildland-agriculture gradient of land-use (Hall et al. 1997). Unfortunately, the most common approach to assessing habitat quality has historically been via assessment of animal numbers (population density); where high densities have been taken as evidence of high quality habitat. In our own work, we have shown that bird densities can be enhanced on farms using attractive plantings (Jones and Sieving 2006) but this does not mean that birds attracted to fields are exposed to beneficial or benign conditions from their perspective. Ecological traps have been defined as attractive habitats that bring species into danger from higher predation, pollution, other mortality factors, or that provide substandard food or other critical resources leading to reproductive failure (Schlaepfer et al. 2002). Such traps could easily be created on farms if species are attracted to use on-farm habitats for foraging (e.g., Jones and Sieving 2006) or for reproduction (e.g., Mols and Vissar 2002) but suffer greater mortality or depressed reproduction as a result.
Our specific objectives were to:
1) Quantify foraging rates of Eastern Bluebirds on reduced-impact (e.g., organic, organically managed, sustainable) farm fields, including a summary of prey types and numbers taken per feeding visit to nest boxes.
2) Estimate pest availability in reduced-impact vegetable fields near bluebird nest-boxes.
3) Conduct nest-monitoring of bluebirds on reduced-impact farms, conventional farms, and natural open lands, allowing us to compare reproductive success among these land-management categories.