Farmland birds in southern Ontario: field use, activity patterns and vulnerability to pesticide use

The use of cropfields by birds is largely unknown in southern Canada and co nsequently the risk incurred by pesticide use on bird populations cannot be adequately characterised. The activity patterns and relative interior to e dge use of bird species were examined for four crops in southern Ontario to assess the susceptibility of different species to pesticide use. Altogethe r 138 species were identified in the four crops over the 2 year period but only 25 species were recorded during 50% of visits in at least 1 month: 14 in corn (Zea mays L.), 16 in soybean (Glycine max L. Merr,), 14 in apple (M alus spp.) orchards and eight in vineyards (Vitis spp.). Territorial behavi our was an important activity for several species from May through July in the four crops. Nesting was confirmed in May June and July for most species , with the exception of American Goldfinch Carduelis tristis, Chipping Spar row Spizella passerina and Cedar Waxwing Bombycilla cedrorum which nested i n August/September. Foraging was the most important activity for most speci es in all months (7/10 species in May, 6/8 species in June, 4/8 species in July, 5/8 August/September). Few fledgling young were observed. Most specie s used field edges consistently more often than expected in corn and soybea n fields, according to the edge/interior ratio, Yellow Warbler Dendroica pe techia being the exception. In apple orchards, relatively few species diffe rentiated between edge and interior. Based on their frequency of occurrence (>50%), behaviour and temporal coincidence with pesticide applications, 13 species were considered most at risk: Killdeer Charadrius vociferus, Horne d Lark Eremophila alpestris, American Crow Corvus brachyrhynchos, American Robin Turdus migrator-ius, European Starting Sturnus vulgaris, Chipping Spa rrow, Vesper Sparrow Pooecetes gramineus, Savannah Sparrow Passerculus sand wichensis, Song Sparrow Melospiza melodia, Red-winged Blackbird Agelaius ph oeniceus, Common Crackle Quiscalus quiscala, Brown-headed Cowbird Molothrus ater and Barn Swallow Hirundo rustica. The latter species, because of its foraging habit, is less likely to be exposed to pesticides. This study was important to identify focal species that can be used for detailed investiga tions on exposure to pesticides. (C) 1999 Elsevier Science B.V. All rights reserved.