Abstract
Agriculture in many regions of the world has reduced bird habitat and abundance, and altered avian community structure. A study was conducted on an organic research farm over two winters (Oct to Mar) in an intensive agricultural region of Salinas Valley, CA to determine how cover crop variety and planting density influenced birds. Cover crops were rye (Secale cereale), a mixture of rye and legumes (Vicia spp., Pisum sativum), and a mustard mixture (Brassica juncea, Sinapis alba). White-crowned Sparrows (Zonotrichia leucophyrs), Savannah Sparrows (Passerculus sandwichensis) and Song Sparrows (Melospiza melodia) were observed both years in the study field. Bird droppings in cover crops were quantified and dissected to determine dietary preferences, and sparrow movement when flushed was determined. Dropping number and weight per m2 were at least 10 times greater in mustard than in rye and in the legume-rye mixture. Droppings were dominated by leaf tissue in mustard versus arthropod tissue in rye and legume-rye. Within cover crop variety, plant density did not have a clear or consistent effect on sparrows. Sparrows flushed from cover crops usually settled in mustard. The White-crowned Sparrow fed on mustard leaves and apparently on weed foliage under mustard. The arthropod-dominated droppings in rye and legume-rye cover crops were consistent with the food preferences of Song and Savannah Sparrows. The White-crowned Sparrow’s clear preference for mustard cover crops is likely due in part to their high dietary needs for sulfur-rich amino acids during the prenuptual molt. This paper provides novel information to help farmers and others understand the cover crop preferences of sparrows, and ways that farmers might use mustard cover crops as trap crops to reduce White-crowned Sparrow feeding damage on winter and spring vegetable crops. It also provides evidence of ecosystems services that these sparrows provide by feeding on weed tissue in winter cover crops.
Highlights
Agricultural intensification during the past 70 years has increased world food supplies several fold through the use of synthetic chemicals, new technologies, and improved crop varieties, but has dramatically altered the earth’s ecosystems (Matson et al, 1997; Tilman et al, 2002)
The dropping data suggest that bird species that fed primarily on leaves, arthropods, and weed seed/fruit tissue preferred the mustard habitat, whereas those that specialized on arthropods and weed seed/fruit preferred rye
This paper provides the first data on sparrow preferences in three broad categories of winter cover crops that are used in high-value vegetable systems in the central coast region of California
Summary
Agricultural intensification during the past 70 years has increased world food supplies several fold through the use of synthetic chemicals, new technologies, and improved crop varieties, but has dramatically altered the earth’s ecosystems (Matson et al, 1997; Tilman et al, 2002) During this period, farmland bird community structure has been altered and populations have declined. Birds in Winter Cover Crops in many regions of the world (Chamberlain et al, 2000; Shutler et al, 2000; Donald et al, 2001; Murphy, 2003; Brennan and Kuvlesky, 2005; Butler et al, 2007; Rosenberg et al, 2019) These reductions are due to habitat loss (Green et al, 2005) and are associated with a reduction in insect and arable weed populations that are a food resource for higher trophic groups including birds (Benton et al, 2002; Storkey and Westbury, 2007). Recent research on strawberry systems in this region highlighted the benefits of maintaining seminatural habitat around farms to help reduce bird damage on strawberries (without increasing food safety risks) and to increase bird diversity (Olimpi et al, 2020)
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