Ke. Freemark et Da. Kirk, Birds on organic and conventional farms in Ontario: partitioning effects of habitat and practices on species composition and abundance, BIOL CONSER, 101(3), 2001, pp. 337-350
Population declines of farmland birds over recent decades in Europe, Canada
and the USA have been attributed to more intensive agricultural management
. We counted birds during the 1990 breeding season on 72 field sites in sou
thern Ontario, Canada, paired between 10 organic and 10 conventional farms
for local habitat to enhance our ability to detect effects of agricultural
practices. Of 68 species recorded, 58 were on organic sites, 59 on conventi
onal. Species richness and total abundance were significantly greater on or
ganic than conventional sites based on log-linear regression. Of 43 species
analyzed with log-linear regression, eight (18.6%) were significantly (P <
0.05) more abundant on organic than conventional sites and four (9.3%) appr
oached significance (0.05 <P <0.10). Eight of these 12 species had negative
population trends for 1967-1998 Breeding Bird Surveys (BBS) in this region
. Two of the 43 species analyzed (4.7%) were significantly more abundant on
conventional than organic sites and three (7.0%) approached significance.
Two of these five species had negative BBS population trends. A canonical c
orrespondence analysis (CCA) of 13 practices and 13 habitat variables expla
ined 44% of total variation (TV) accounted for in a detrended correspondenc
e analysis of bird species composition and abundance. Practices contributed
23.7% of TV, habitat 26%; habitat and practices shared 5.7% with each othe
r and 12% with farm ownership (i.e. clustering of field sites within farms)
. CCA ordinations indicated considerable mixing of organic and conventional
sites across a gradient from sites with many birds species associated with
greater habitat heterogeneity and more pasture, winter grain, farmstead an
d other non-crop habitats (hedgerow, woodland) to sites with few bird speci
es associated with larger fields, more rowcrop and spring grain, more passe
s and tilling, and use of herbicides and chemical fertilizers. Our results
re-emphasize the importance of non-crop habitats, more permanent crop cover
, and less intensive management practices to the conservation of avian biod
iversity on farmland. Canadian Crown Copyright (C) 2001 Published by Elsevi
er Science Ltd. All rights reserved.