Are bluebirds good for farms, and are farms good for bluebirds?
In the dry 2007 breeding season, we researched the effects of farm-management (reduced-impact farms, conventional farms, and natural control areas) on the reproductive success of Eastern Bluebirds (Sialis sialia). Bluebirds produced the same amount of fledglings over the breeding season across all treatments, yet those on both farm treatments had to produce more clutches and eggs to match the reproductive output of control bluebirds. We are continuing this research in 2008.
We are determining the pest-eating potential of bluebirds and on-farm prey population size on reduced-impact farms through the use of motion-sensor cameras, behavioral observations, and arthropod surveys on farms.
1) Quantify foraging rates of up to three or four species of insectivores commonly observed in fields in spring and fall, including a summary of prey types and numbers taken per unit time of foraging, and distribution of foraging time by insectivorous birds with respect to field lay-out.
2) Estimate leaf-chewing pest availability (density / species composition) in areas where birds forage in vegetable fields.
3) Conduct nest-monitoring and habitat use studies of Eastern Bluebirds on vegetable farms with different levels of insecticide application (up to 150 different pairs, and 450 nests per season). Nest-boxes will be placed in farm fields, near forest edges, in a standardized and replicated fashion. This objective will help determine:
A) how much field area does an adult bird use to forage
B) prey-delivery rates to nestlings (by monitoring focal birds at nest boxes), and
C) reproductive success in relation to farm management.
1) Foraging rates, etc.: In the 2007 field season, we originally aimed to quantify the foraging rates of several species of common pest-eating birds. This objective was written with the notion that we would be receiving additional money through a separate and larger SARE proposal which was not funded. Without this money, we did not have the human resources to obtain sufficient sample sizes to determine the foraging rates of several species of birds.
We therefore developed an alternate way to address this objective. We erected nest-boxes for Eastern Bluebirds (one of the 3 most common species of pest-eating birds in this region) on farms in order to be able to observe what amount and type of prey males brought to incubating females, and what males and females brought to their nestlings. With the help of undergraduate volunteers, we were able to collect some preliminary observations through the use of direct nest-box observations with binoculars. This technique worked but required a lot of field-hours, and we were only able to sample at certain hours of the day.
In the 2008 field-season, we have found and even better technique to quantify the foraging rates of bluebirds. We have placed motion-sensing cameras over the nest-boxes to record foraging rates and to identify prey items brought to the nest-box by parent birds. We also plan to track, as best as we can, the habitat-use of adult bluebirds in order to determine if the majority of their foraging occurs on the farm-field itself. These data will allow us to confidently estimate the foraging rates of bluebirds across the growing season and throughout all hours of the day, while roughly understanding how much of that prey comes from farm-fields.
2) On-farm arthropod populations: We have conducted hundreds of surveys for arthropods and have many more to do in the remaining months of the 2008 growing season. We are walking 20-m line-transects in non-crop vegetation within and around crop-fields to count orthoptera and lepidoptera, a standard method in the scientific literature. We have also developed another transect method that is relevant to ground-foraging insectivorous birds such as bluebirds, and allows us to quantify in-field prey populations. In this method, we walk for 10 m and record anything that we see within an arm’s length, and then we crouch and brush the vegetation for 10 m, again recording anything within an arm’s length. Prey items are generally identified to Order.
3) Eastern Bluebird Studies: Part 1 above addresses progress related to Objectives 3a and 3b. Much of 2007, and part of 2008, has been spent addressing Objective 3c. By placing nest-boxes on reduced-impact farms, conventional farms, and natural control areas, we have tested for the effects of farm-management on the reproductive success of bluebirds. Our biggest result so far is that birds on farms, in general, produce more clutches than birds in natural control areas, yet birds in all 3 treatments produced a statistically similar number of fledglings (although those on reduced-impact farms did produce the most). As we collect more reproductive success data in this wetter year of 2008, we will see if the same pattern holds true. After this, we will be able to make well-informed statements about the habitat suitability of farmlands for breeding bluebirds.
Impacts and Contributions/Outcomes
Many farmers have enjoyed learning about the pest-eating bluebirds on their fields and are very thankful to have more there, thanks to the nest-boxes which we erected. The bulk of our contributions will come at the end of this research, when we are able to send extension articles to farmers. In these articles, we will let them know how bluebirds fare in different landscapes and how many pests the average pair of bluebirds eats on a farm in relation to the number of pests in the field. We will also distribute information on how to attract beneficial birds to their lands through the correct placement of nest-boxes, the planting of certain inter-crops, etc.