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Habitat Associations of Priority Bird Species and Conservation Value on Small, Diversified Farms in New England

In recent decades, New England agriculture has become increasingly characterized by small, diversified farming operations with values deeply rooted in community and conservation. In sharp contrast to large-scale, high-intensity agriculture currently typified by the majority of North American farms, New England farmers commonly prioritize ecologically beneficial production practices such as reduced chemical inputs, integrated pest management (IPM), low tillage, cover cropping and crop rotation, and retention of natural habitats like woody hedgerows and herbaceous strips. Public support and demand for local, sustainable food, evidenced by the success of CSA (Community Supported Agriculture) in the region, has helped to bolster this movement and increase the viability of these farms. In addition to boosting regional food production and self-sufficiency, these farms also present an opportunity for wildlife conservation. Shrubland bird species in particular may benefit from habitat created on these farms because of their preference for heterogeneous shrub and herbaceous vegetation and lower area sensitivity compared to other species, such as grassland obligates. In order to evaluate conservation potential and habitat associations of shrubland birds and other priority species on small, diversified farms, we conducted point counts and vegetation surveys across 23 farms in the Pioneer Valley, MA during the summers of 2017 and 2018. We used Poisson-binomial mixture models and canonical correspondence analysis (CCA) to assess the effects of a suite of microhabitat-, field-, and landscape-scale variables on the abundance of bird species. Our results confirmed that shrubland birds, including song sparrow (Melospiza melodia), gray catbird (Dumatella carolinensis), common yellowthroat (Geothlypis trichas) and American goldfinch (Spinus tristis), were the predominant species present, accounting for over 52% of the total observations. Species-habitat relationships were diverse; however, smaller field sizes, and increased cover of tall, dense, woody or nonproductive vegetation types were associated with higher abundance of shrubland species as well as lower abundance of crop pests such as European starling (Sturnus vulgaris) and house sparrow (Passer domesticus). These findings support the hypothesis that small, diversified farms are providing beneficial habitat for shrubland birds, as well as providing species-specific guidelines for farmers interested in conserving birds on their land. In order to place small, diversified farms into a regional conservation context and evaluate their contribution to shrubland bird conservation efforts in New England, we compared bird abundance, community composition, and conservation value of small, diversified farms to five established shrubland habitat types in the region: wildlife openings, two types of silvicultural openings (larger clearcuts and small forest openings created by group selection harvest), beaver meadows, and powerline rights-of-way. We compiled avian survey data from previous studies of each of the aforementioned habitat types conducted from 2002-2006 (powerline rights-of-way, wildlife openings, clearcuts, and beaver meadows) and 2014 (small forest openings). We then compared the relative bird abundance, community composition, and conservation value across all five habitat types (including farms) using Generalized Linear Models (GLMs), non-metric multidimensional scaling (NMDS) ordination, permutational multivariate analysis of variance (PERMANOVA), and calculated an Avian Conservation Significance (ACS) score for each habitat. The avian community composition of farms most closely resembled that of wildlife openings and harbored more open-habitat and generalist species such as American robin (Turdus migratorius), red-winged blackbird (Agelaius phoeniceus), and eastern kingbird (Tyrannus tyrannus). Several shrubland species were found to have higher relative abundances on farms than any of the other four habitats including song sparrow (Melospiza melodia), northern cardinal (Cardinalis cardinalis), and willow flycatcher (Empidonax traillii). Farms possessed a higher ACS score than powerline rights-of-way, small forest openings, and beaver meadows, but were lower than clearcuts and wildlife openings. Our results suggest that small, diversified farms support a unique suite of shrubland species, and while they certainly cannot replace managed shrubland habitats such as wildlife openings and clearcuts, they may complement these existing habitats in terms of their community composition and conservation value.
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