Pierre Mineau

The impact of agricultural practices on biodiversity

Abstract Agricultural activities such as tillage, drainage, intercropping, rotation, grazing and extensive usage of pesticides and fertilizers have significant implications for wild species of flora and fauna. Species capable of adapting to the agricultural landscape may be limited directly by the disturbance regimes of grazing, planting and harvesting, and indirectly by the abundance of plant and insect foods available. Some management techniques, such as drainage, create such fundamental habitat changes that there are significant shifts in species composition. This paper considers the relative merits of conventional tillage versus reduced, or no-till farming, and reviews the benefits of rest-rotation grazing, crop rotation and intercropping in terms of maintaining wild species populations. There are a number of undesirable environmental impacts associated with fertilizer and pesticide usage, and in this paper we attempt to provide an account of the ways in which these inputs impact on biodiversity at various levels including plant, invertebrate, and vertebrate groups. Factors which are considered include the mobility, trophic interactions, persistence, and spectrum of toxicity for various pesticides. The ecological virtues of organic and inorganic fertilizers are compared, and the problems arising from excessive use of fertilizer are discussed. The findings in this review indicate that chemical fertilizer loadings must be better budgeted to not exceed local needs, and that pesticide inputs should be reduced to a minimum. The types and regimes of disturbance due to mechanical operations associated with agricultural activity may also be modified to help reduce negative impacts on particular groups of species, such as birds. For those plant and insect species which need to be controlled for agronomic reasons, the population decreases brought about by disturbance regimes may be desirable as a form of pest management. The prevalence of agriculture over such a large portion of the Canadian landscape means that it is important that we find solutions to conflicts that arise between agriculture and wild species. It is important to realize that the impact of agricultural inputs varies greatly among regions and species, and actual effects have generally not been investigated for many species in any one locality; while the focus of this review is on Canada, much Canadian-specific research is lacking, thus, this review also draws from relevant research done elsewhere.

Rape in the Lesser Snow Goose

Rape attempts were found to be a consistent feature of Lesser Snow Goose biology. In the light of attendant male behaviour in response to a rape attempt on his mate as well as rapist behaviour and chronology of rapes relative to nesting, it is suggested that rape is part of the overall reproductive strategy of the male and therefore, evolutionarily relevant.

Pesticide acute toxicity is a better correlate of U.S. grassland bird declines than agricultural intensification.

Common agricultural birds are in decline, both in Europe and in North America. Evidence from Europe suggests that agricultural intensification and, for some species, the indirect effects of pesticides mediated through a loss of insect food resource is in part responsible. On a state-by-state basis for the conterminous Unites States (U.S.), we looked at several agronomic variables to predict the number of grassland species increasing or declining according to breeding bird surveys conducted between 1980 and 2003. Best predictors of species declines were the lethal risk from insecticide use modeled from pesticide impact studies, followed by the loss of cropped pasture. Loss of permanent pasture or simple measures of agricultural intensification such as the proportion of land under crop or the proportion of farmland treated with herbicides did not explain bird declines as well. Because the proportion of farmland treated with insecticides, and more particularly the lethal risk to birds from the use of current insecticides feature so prominently in the best models, this suggests that, in the U.S. at least, pesticide toxicity to birds should be considered as an important factor in grassland bird declines.

Second generation anticoagulant rodenticides in predatory birds: Probabilistic characterisation of toxic liver concentrations and implications for predatory bird populations in Canada.

Second-generation anticoagulant rodenticides (SGARs) are widely used to control rodent pests but exposure and poisonings occur in non-target species, such as birds of prey. Liver residues are often analysed to detect exposure in birds found dead but their use to assess toxicity of SGARs is problematic. We analysed published data on hepatic rodenticide residues and associated symptoms of anticoagulant poisoning from 270 birds of prey using logistic regression to estimate the probability of toxicosis associated with different liver SGAR residues. We also evaluated exposure to SGARs on a national level in Canada by analysing 196 livers from great horned owls (Bubo virginianus) and red-tailed hawks (Buteo jamaicensis) found dead at locations across the country. Analysis of a broader sample of raptor species from Quebec also helped define the taxonomic breadth of contamination. Calculated probability curves suggest significant species differences in sensitivity to SGARs and significant likelihood of toxicosis below previously suggested concentrations of concern (<0.1mg/kg). Analysis of birds from Quebec showed that a broad range of raptor species are exposed to SGARs, indicating that generalised terrestrial food chains could be contaminated in the vicinity of the sampled areas. Of the two species for which we had samples from across Canada, great horned owls are exposed to SGARs to a greater extent than red-tailed hawks and the liver residue levels were also higher. Using our probability estimates of effect, we estimate that a minimum of 11% of the sampled great horned owl population is at risk of being directly killed by SGARs. This is the first time the potential mortality impact of SGARs on a raptor population has been estimated.

Past and Current Attempts to Evaluate the Role of Birds as Predators of Insect Pests in Temperate Agriculture

Many bird species consume large quantities of invertebrates, some of which are considered agricultural pests. However, relatively few quantitative studies demonstrate that avian predators can reduce agricultural insect pests below a level at which unchecked populations would cause economic damage to crops or require treatment with pesticides. In fact, since the subject of economic ornithology (“all relations of birds that has any bearing upon the material welfare of [humans]”— McAtee, 1933) was last reviewed (e.g., McFarlane, 1976; Sweetman, 1958), there have been only a handful of published studies on the role of birds in agricultural ecosystems, and most of these refer to small-plot effects, with no attempt to aggregate the results at the level of an agricultural economic unit, i.e., the farm.

Intraspecific nest parasitism and extra-pair copulation in lesser snow geese

Intraspecific nest parasitism and extra-pair fertilization contributed significantly to individual reproductive success in a colony of plumage polymorphic lesser snow geese,Chen caerulescens caerulescens, studied for 14 years in northern Manitoba, Canada. Parasitic females preferred to lay in or adjacent to occupied, defended nests, rather than undefended nests. Nesting females usually rolled eggs that had been laid nearby into their nests. Nest-attendant males typically attacked the intruding females mate, who usually remained at a short distance, thereby drawing the resident male away from the nest. Plumage genetics were used to estimate rates of both nest parasitism and extra-pair fertilization. Nests of homozygous dominant blue morph pairs produced 4·03% homozygous recessive white goslings (N = 4938), which must have been unrelated to both parents, providing information on the rate of nest parasitism. Nests of homozygous recessive white morph pairs produced 2·12% blue goslings (N = 45 777), which must have been unrelated to either one or both parents, providing information on the rate of nest parasitism plus extra-pair fertilization. Using colony-wide estimates of the colour ratio of goslings produced (28·5% blue) and of the blue allele frequency in males (21%), it was calculated that nest parasitism accounted for 5·6% of hatching goslings, and that 2·4% of goslings were fathered by extra-pair fertilization.

Brodifacoum Poisoning of Avian Scavengers During Rat Control on a Seabird Colony

Langara Island, at the north-western tip of British Columbias Queen Charlotte archipelago, was once nesting grounds for an estimated 500,000 seabirds. However, infestations of Norway rats (Rattus norvegicus) and their predation of eggs and breeding adults have caused extirpation or serious declines of all seabird species. By 1993, the breeding population of ancient murrelets (Synthliboramphus antiquus) had declined to 10% of its historical size. Successful eradication of rats on smaller New Zealand islands using the anticoagulant brodifacoum prompted its application on Langara Island. The island is also home to breeding bald eagles (Haliaeetus leucocephalus), peregrine falcons (Falco peregrinus), and other wildlife. No comprehensive studies of non-target impacts and potential for secondary poisoning were done during similar operations elsewhere; thus, in 1994 and 1995 we initiated a two-year study into the risk of secondary poisoning to non-target species. During 1994, rat carcasses were laid out with motion sensor cameras to identify potential scavengers. Ravens, northwestern crows and bald eagles were photographed at carcasses, and therefore at risk of feeding on rats that die above ground. During the baiting program, 19 rats were radio-tagged to determine the proportion dying above ground, and thus available to predators/scavengers. Ravens were found poisoned both from feeding directly on the bait, and predating/scavenging poisoned rats. Bald eagles were trapped and blood sampled for brodifacoum residue analysis and prothrombin time evaluation; 15% of the sampled population showed detectable residues but no adversely-affected birds were found. We conclude that the use of brodifacoum for rat removal on seabird islands poses a clear risk of secondary poisoning to avian scavengers. This risk must be weighed against the benefit of rat removal programs.

POISONING OF BALD EAGLES AND RED-TAILED HAWKS BY CARBOFURAN AND FENSULFOTHION IN THE FRASER DELTA OF BRITISH COLUMBIA, CANADA

During the winter of 1990 in the Fraser Delta of British Columbia, Canada, nine birds of prey were found with symptoms of anticholinesterase poisoning. Immediate surgical removal of crop contents of three birds decreased mortality and recovery time. Chemical analysis was conducted on crop contents, which contained mainly duck parts. A bald eagle (Haliaeetus leucocephalus) contained 200 μg/g and a red-tailed hawk (Buteo jamaicensis) 2.2 μg/g carbofuran, while the crop of another red-tailed hawk contained 30 μg/g fensulfothion. There was evidence that granular carbofuran and fensulfothion persisted long enough in the wet, low pH conditions of the Fraser Delta to kill waterfowl and cause secondary poisoning of raptors several months after application of the pesticides.

An Estimate of Avian Mortality at Communication Towers in the United States and Canada

Avian mortality at communication towers in the continental United States and Canada is an issue of pressing conservation concern. Previous estimates of this mortality have been based on limited data and have not included Canada. We compiled a database of communication towers in the continental United States and Canada and estimated avian mortality by tower with a regression relating avian mortality to tower height. This equation was derived from 38 tower studies for which mortality data were available and corrected for sampling effort, search efficiency, and scavenging where appropriate. Although most studies document mortality at guyed towers with steady-burning lights, we accounted for lower mortality at towers without guy wires or steady-burning lights by adjusting estimates based on published studies. The resulting estimate of mortality at towers is 6.8 million birds per year in the United States and Canada. Bootstrapped subsampling indicated that the regression was robust to the choice of studies included and a comparison of multiple regression models showed that incorporating sampling, scavenging, and search efficiency adjustments improved model fit. Estimating total avian mortality is only a first step in developing an assessment of the biological significance of mortality at communication towers for individual species or groups of species. Nevertheless, our estimate can be used to evaluate this source of mortality, develop subsequent per-species mortality estimates, and motivate policy action.

SECONDARY POISONING OF EAGLES FOLLOWING INTENTIONAL POISONING OF COYOTES WITH ANTICHOLINESTERASE PESTICIDES IN WESTERN CANADA

Records of eagles, coyotes (Canis latrans), and red foxes (Vulpes vulpes) necropsied at the Western College of Veterinary Medicine, Saskatoon, Saskatchewan, Canada, between 1967 and 2002 were reviewed for cases suggestive of anticholinesterase poisoning. From 1993 to 2002, 54 putative poisoning incidents involving 70 bald eagles (Haliaeetus leucocephalus) and 10 golden eagles (Aquila chrysaetus) were identified. Of these, 50 incidents occurred in Saskatchewan, two were in Manitoba, and one occurred in each of Alberta and the Northwest Territories. The diagnosis was confirmed in eight instances by demonstration of pesticide in ingesta from eagles or known use of pesticide at the site together with brain cholinesterase (AChE) reduction of >50% in at least one animal. A presumptive diagnosis of poisoning was made in 33 incidents based on brain AChE reduction of >50% in at least one animal; 13 incidents were considered suspicious because of circumstantial evidence of the death of eagles in association with other species and limited AChE reduction. Other wild species were found dead in 85% of the incidents involving eagles. Coyotes, foxes, black-billed magpies (Pica pica), and striped skunks (Mephitis mephitis) were associated with 34, six, six, and three incidents, respectively. There were eight additional incidents that did not involve eagles in which poisoning was diagnosed in coyotes. Carbofuran was identified in nine incidents. Carbamate poisoning was indicated on the basis of reactivation of brain AChE activity in two additional incidents. Brain AChE activity was not reduced from normal in eagles in four of seven incidents in which carbofuran was identified. The organophosphorous insecticide terbufos was found together with carbofuran in one incident. Brain AChE activity was measured in wild canids and in eagles in 15 incidents; in all of these incidents, brain AChE was reduced by >50% in at least one mammal, whereas this level of reduction occurred in eagles in only four incidents. Use of anticholinesterase pesticides to poison coyotes is illegal, but the practice continues and secondary poisoning of eagles is a problem of unknown proportions in western North America.