Wildlife Biology 2 (1), 1-9, (1 March 1996) https://doi.org/10.2981/wlb.1996.002
KEYWORDS: pink-footed goose, fungicide, Imazalil, Thiram, feeding ecology
The Svalbard population of pink-footed geese Anser brachyrhynchus is concentrated in western Jutland, Denmark, from early March to early May. During spring, the geese shift feeding habitat from grasslands and stubble fields to new-sown fields. To avoid crop damage, grain bait is provided at five sites. The aim of this study was to quantify the exposure of geese to, and the ingestion rates of, pesticide-treated seeds, and to evaluate the potential effects at the individual and the population level. During spring 1994, approximately 7% and 1 % of the total number of goose-days were spent on new-sown cereal fields and new-sown pea fields, respectively. After the commencement of sowing, about 25% of all goose-days were spent in new-sown fields. Late-departing individually marked geese made more frequent use of new-sown fields than early-departing individuals (P < 0.001). Geese foraged intensively in new-sown fields early in the morning and sometimes late in the evening. Due to high feeding profitability of the new-sown grain compared to grass, the geese obtained half or more of their daily energy intake by feeding on new-sown cereal fields, even where bait grain was provided. Spring-sown barley is treated with the fungicide Imazalil and peas are usually treated with Thiram. The daily Imazalil ingestion rate by an 'average' goose was estimated at 9–15 mg active ingredient (a.i.), or 3–-5 mg a.i./kg body mass, which is two orders of magnitude below reported LD50 values for various species of test birds. Imazalil may have sub-lethal effects, especially on geese using the new-sown cereal fields for consecutive days, but the low toxicity and high mobility of the compound suggest that effects are minor and short-lived. The daily Thiram ingestion rate by the geese was not quantified, but it is calculated that a goose would have to eat about 100 g of peas to reach a level of Thiram ingestion (200 mg/kg diet), which could have sub-lethal effects on reproductive parameters. A goose foraging on new-sown peas can accomplish this within less than one hour. Special management precautions should be taken to deter geese from exploiting new-sown pea fields.