PS 8-105 - Birds of a feather: temporal and spatial relationships of farm birds in hazelnut orchards

Abstract: Bird populations are decreasing worldwide, predominantly from loss of habitat. In North America, remnant wildland habitats are dispersed throughout a matrix of agricultural land, creating complex interactions between habitat elements and management practices. For example, the state of Oregon produces almost all U.S. hazelnuts, and orchards have replaced much of the historic oak-prairie habitat. The industry is expected to double in the next decade, increasing the extent of habitat loss and shifting the age structure of hazelnut orchards from old to young. The degree to which hazelnut orchards support bird populations, and how this depends on adjacent habitat and orchard age, are open questions critical to bird conservation in this changing landscape. Here I conducted an observational survey of birds within hazelnut orchards during the 2022 breeding season, performing bi-weekly point counts of farm bird communities from March to August. I sampled at three large-scale hazelnut operations in Oregon, and first contrasted bird abundance and diversity between a farm in a complex landscape matrix (mixture of old and young orchards, adjacent to oak-prairie savannah, riparian forest, and urban habitat; Dorris Ranch) to two farms of decreasing landscape complexity (e.g. increasing agriculture context), finding that both metrics were considerably higher in a diverse landscape matrix. Focusing on Dorris Ranch, I then asked: (i) what diversity and type of birds utilize hazelnut orchards of different ages; and, (ii) how do different adjacent wildland habitat types affect species diversity? I found that (1) younger orchards had higher species richness, yet farm bird communities were more homogenous than older orchards (i.e. higher ratio of generalist species to specialists); (2) adjacent oak habitat had a moderate positive effect on species richness, particularly near younger orchards; (3) species richness and abundance were moderately higher in the younger orchards during the late season; and, (4) diet guilds of bird communities varied by orchard age throughout time. Several strategic species for conservation in Oregon utilize orchards of different ages throughout the year – such as western bluebirds and acorn woodpeckers in younger orchards, and white-breasted nuthatches and chipping sparrows in older orchards. Moreover, foliage gleaners, like black-capped chickadees, where most abundant in older orchards and are known to be beneficial for pest control. Ultimately this case-study serves to inform the conservation of native habitat and orchard complexity within the agricultural-wildland matrix to increase ecosystem services for farms, while simultaneously buffering biodiversity loss across the landscape.