Dr. Scott Petrie, Long Point Waterfowl Executive Director
Dr. Liana Zanette, University of Western Ontario
Historically, waterfowl did not acquire much of their daily energy intake from agricultural sources. However, with increases in row crop farming and modern agricultural practices, waterfowl now have access to a highly nutritious and readily available food source. Many waterfowl now rely heavily on waste grains such as corn, wheat and rice to meet their daily energy needs. Several waterfowl species wintering in southern Ontario depend almost solely on waste corn until wetland plants are again available to eat in spring. Numerous species also acquire the energy needed for spring and fall migration from waste grains. Waste grains are critically important during spring because senescence of aquatic plants and ice cover during winter limits foraging opportunities in wetlands. Waste grains contain high amounts of carbohydrates which are readily converted by waterfowl into the fats and lipids necessary for their migration and reproduction. Consequently, increased consumption of waste grains has lead to population increases in many field-feeding waterfowl. For instance, agricultural grain consumption has contributed to the rapid increase in Canada Geese, Lesser Snow Geese, and Tundra Swan populations throughout North America.
Farmers strive to increase their profit margins, particularly since grain prices are highly variable. As a result, farm machinery manufacturers have produced combines with increased harvest efficiency. This increase in efficiency may result in an overall decrease in waste corn available to field-feeding waterfowl. Post-harvest tillage practices, such as disking and plowing, also likely contribute to a decrease in waste grain availability for field-feeding waterfowl. Studies in Illinois have shown that with modern combines and post-harvest tillage practices waste grain availability can be reduced by as much as 99%. Such decreases in waste grains could significantly reduce forage for field-feeding waterfowl. This may be particularly problematic in spring when birds acquire the nutrients necessary for migration and reproduction. Reductions in waste grain availability therefore could lead to significant impacts on the conservation and management of field-feeding waterfowl.
Recent increases in global temperatures could also impact the nutritional content or availability of waste grains for field-feeding waterfowl. For instance, the continued freeze-thaw cycle experienced during recent winters may result in higher rates of decomposition than in the past. Increased rates of decomposition would result in a decrease in the nutritional quality of the waste grains available to spring staging waterfowl when waste grain is of high reproductive importance. Warmer winters also results in more waterfowl staying on the Lower Great Lakes during winter. Increases in overwintering populations of field-feeding waterfowl, combined with decreases in availability and nutritional quality of waste grains, could result in food availability or quality declining below critical thresholds for spring migrants.
There have also been substantial increases in many other species of wildlife that utilize waste grains as a food resource. For example, White-tailed Deer, Wild Turkey and Raccoon populations have all been rapidly expanding and each of these species rely heavily on agricultural waste grains. Competition for food with these species may also limit the ability of waterfowl to obtain essential nutrients required for migration and reproduction.
Study Objectives and Hypotheses
The objectives of this study were to document the dynamics of waste corn availability and nutritional quality in relation to field-feeding waterfowl use near Long Point, Ontario. It was hypothesized that fields harvested with newer more efficient combines will have less waste corn available than fields harvested with older less efficient combines. Second, it was hypothesized that waste corn availability would decline between fall harvest and late spring migration due to consumption by waterfowl and other wildlife. Third, it was hypothesized that waste corn nutritional quality would be significantly less in spring than fall due to continual freezing and thawing over the winter. Lastly, it was hypothesized that field-feeding waterfowl would utilize fields with the most available corn.
Landowners were contacted and surveyed to determine age (efficiency) and type of combine as well as type of post-harvest tillage applied to harvested corn fields. A random transect design was used to sample harvested corn fields. A 1m2 quadrat was used to sample harvested corn fields at a frequency of one sample per acre. Fields were sampled right after harvest in fall and in spring, waterfowl migration. Samples were dried at 60 degrees Celcius for 48 hours. Final weights were used to extrapolate total amounts of waste corn available after harvest.
Sub-samples of dried corn were shipped to a lab so that total percent starch, fats, lipids and minerals could be analyzed for each field. Fall samples were compared to spring samples (within fields) to detect any seasonal changes in nutritional quality of waste corn.
Terrestrial field-feeding waterfowl surveys were conducted three times a week during fall migration and daily during spring migration to quantify field selection. Surveys were conducted morning and afternoon and species, flock size, distance from field edge and individual field location of birds were recorded. Other field feeding species such as American Crows, White-tailed Deer and Wild Turkeys were also recorded if present.
Brief Results and Discussion
Average initial waste corn densities of 188 kg/ha found at Long Point were similar to densities reported at other northern staging areas. Final spring densities decreased to 62 kg/ha, potentially limiting to spring staging waterfowl. The number of other wildlife-use-days and the distance a field was located from Lake Erie were the two variables that significantly decreased waste corn density. No relationship was found between initial corn density and harvester age (proxy for efficiency) during either study year. Only 5% of fields were plowed or disked during the study period. The waste corn density in these fields was reduced by 97%. Promotion of no-till farming practices by conservation groups in the area may offset any decreases in waste corn density through increased harvester efficiency or post-harvest tillage.
A significant decrease in waste corn nutritional quality (% carbohydrates) was observed. However, this decrease in quality was not correlated to initial percent moisture of waste corn. Currently the affect of increasing winter temperature on spring waste corn nutritional quality is unclear. Long-term studies are required to better understand the relationship between nutritional quality of waste corn and increasing winter temperatures.
Field-feeding waterfowl selected fields based on physical characteristics (e.g. field size) rather then initial waste corn density. More field-feeding waterfowl were observed in the spring feeding in fields. This suggests that wetland based foods may be limited during spring, increasing the importance of waste corn for some species of spring staging waterfowl.
Managers should promote the application of no-till farming in areas where waste corn availability may be limiting as a result of increased harvester efficiency. Promotion of no-till farming in areas where post-harvest tillage practices are currently being applied or in areas where corn acreage is declining could also increase the amount of waste corn available to field-feeding waterfowl.
Long Point Waterfowl wishes to thank all of the landowners who have granted me permission to sample their fields. Without their permission, my project would not have been possible. Thank you also to Ross Wood, the field assistant for this research project, for all of his help in the field. Lastly, we wish to thank the following institutions for their generous financial and logistical support:
Long Point Waterfowl, Canadian Wildlife Service, Ontario Ministry of Natural Resources, Ontario Federation of Anglers and Hunters, Ducks Unlimited Canada, Delta Waterfowl, Long Point Waterfowlers Association, Bird Studies Canada, the University of Western Ontario