Conservation Science in the RSPB 2006

40
Woodpigeon
Andy Hay (rspb-images.com)
GMHT cropping and
food for farmland birds
By 1999, several genetically
modified herbicide-tolerant
(GMHT) crops had reached the
final stages of UK government
approval prior to commercial
cultivation. Each crop had been
modified so that, when treated
with a broad-spectrum herbicide,
most weeds would be killed while
the crop remained unharmed.
There was concern that use of
such herbicides might exacerbate
declines in the weed flora and
those bird species dependent
upon it for seed food. Recognising
these concerns, the UK
Government commissioned the
farm-scale evaluations (FSEs) to
investigate the effects of the
management of GMHT crops on
farmland wildlife.
More than 60 fields of each of four
crops, spring and winter oilseed
rape, beet and maize, were split in
half. One half was sown with a
conventional variety and managed
according to normal practice, the
other with a GMHT variety with
weeds controlled by a broadspectrum
herbicide. Along with a
wide range of other measures, the
amount of seed shed (‘seed rain’)
from weeds known to be
important in the diets of 17
seed-eating farmland birds
was compared.
In beet and spring rape, ‘seed rain’
of weeds important in the diets of
16 species was reduced in GMHT
half fields compared to
conventional halves; for no species
did it increase. In winter rape,
‘seed rain’ was reduced in GMHT
halves for 10 species; for only one
did it increase. By contrast, in
maize, ‘seed rain’ was greater in
Ratio of the rain of weed seeds important in each bird species diet in the GMHT compared to the conventional
half for each crop; where this is more than 1, seed rain was greater in the GMHT half, and vice-versa. Each bar
refers to a species; dark bars were statistically significant, the remainder were not.
10
More in GMHT
Ratio (log scale)
1
0.1
More in Conventional
Beet Maize Spring rape Winter rape