The influence of fasting on blood and plasma composition of herring gulls (Larus argentatus)

Populations of scavenging seabird species in the North Sea may fluctuate wi th an artificial food source: the availability of fishery waste. To documen t this impact, it is necessary to assess the birds' nutritional status duri ng periods with decreased fishing activity. Reference data for this purpose was collected from 22 herring gulls investigated during laboratory fasting . After 6 d of food deprivation and body mass losses exceeding 15%, the fir st birds entered starvation phase 3. Comparatively this is a rather weak fa sting capacity. Plasma levels of total protein and thyroid hormones decreas ed and beta-hydroxybutyrate increased with fasting duration. The leucocyte proportions were shifted from lymphocytes to heterophils. After 3 d of refe eding, most of the fasting changes were reversed. Plasma enzyme activities increased and hematocrit, hemoglobin, and erythrocyte numbers decreased in both fasting and control birds, most likely as a result of experimental str ess and repeated blood sampling. Glucose, cholesterol, monocytes, basophils , and glycosylated hemoglobin remained fairly constant. Triglycerides, free fatty acids, uric acid, and urea varied significantly, but changes were no t as clearly a result of fasting. Therefore, total protein, beta-hydroxybut yrate, triiodothyronine, thyroxine, and lymphocyte and heterophil percentag es may be the most reliable indicators of the nutritional status and the co ndition of free-living herring gulls.