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The diet of young capercaillie Tetrao urogallus chicks in Scotland was assessed from analysis of their faeces, collected at the roost sites of broods with radio-marked mothers. Lepidoptera larvae were their main invertebrate food and bilberry Vaccinium myrtillus their main plant food. The concentration of larval remains in the chicks' droppings was correlated with the abundance of larvae found by sweep netting in nearby vegetation. Broods of chicks with the greatest concentration of larval remains in their droppings survived best. Sweep netting for larvae in a semi-natural pine forest in June 1991–1996 showed that larval size, abundance and timing differed among years, and that the sites with the most larvae also differed from year to year. In the same forest, we estimated capercaillie breeding success from hens and chicks found during dog counts. The average number of young per hen in July was correlated with the size, rather than the abundance, of larvae in mid June.
Earlier reports from Fennoscandia and Russia have shown that among adult capercaillies the proportion of females is 60–65%, mainly as a consequence of high mortality of male chicks during their first months of life. The Finnish August censuses of grouse (1964–1988) show that the percentage of female capercaillie has remained unchanged at about 60–65% in northern and eastern Finland. Over the same period the percentage of females in southern and central Finland has decreased significantly from 62 to 50%. The present geographical variation in the percentage of females seems to coincide with the amount of forest in the landscape; the proportion of females is lowest in the southern and western part of Finland where the proportion of agricultural land is highest. Data from 1989–1996 show that variation in August male density among game management districts in Finland (CV%: 21.9) is significantly smaller than that of females (CV%: 33.4). This suggests that the variation in female proportion is more dependent on variation in female than in male density. The most probable reasons for the change in sex ratio include predation on females by mammalian and avian predators and selective hunting (or closing of hunting seasons), but tests of these hypotheses are premature at present.
We tested whether lead exposure, as evidenced by liver lead concentration, affected body composition and organ sizes of canvasback ducks Aythya valisineria in Louisiana during winter 1987–88. After adjusting for body size, sex, age, and site and month of collection, we found decreases in ingesta-free body mass; breast, leg, and body protein; body fat; intestine length; and liver and gizzard masses associated with increased liver lead concentrations. There were no apparent associations between liver lead concentrations and testes and body ash masses, or caecal length. We used the concentration of 26.7 ppm of liver lead on a dry matter (dm) basis as indicative of lead toxicosis. We predicted that a canvasback with 26.7 ppm dm liver lead would weigh 209 g less and have 105 g less fat than an unexposed individual. Whereas many lead exposed canvasbacks may survive through winter, their subsequent survival, ability to reproduce and perform other annual cycle events may be compromised. We recommend management to make lead unavailable to waterfowl at major concentration areas and periodic monitoring of lead contamination in waterfowl populations.
Malaysian populations of ‘edible-nest’ swiftlets (Aves: Apodidae) have declined markedly over the last century. These declines are attributed principally to deleterious effects of nest-harvesting on swiftlet reproduction. The aim of this study was to quantify the impact of nest-harvesting on the reproductive success of the black-nest swiftlet Aerodramus maximus at Gomantong Caves (Sabah), and predict whether sufficient nestlings are allowed to fledge to maintain the population. Experimental nests were harvested at both the beginning and the end of one breeding season. The manipulation had a significant effect; although all harvested nests were subsequently rebuilt they fledged 17% less nestlings than unharvested controls during the breeding season. Also, the time period between eggs and nestlings appearing in nests, and the time period which nestlings spent in the nest, were both significantly longer at experimental nests than at unharvested controls. This implies that nest-harvesting increases the energetic stress of breeding adult swiftlets. Theoretically, however, enough nestlings do fledge from harvested nests at Gomantong Caves to maintain the population of black-nest swiftlets.
The haulout pattern of seals, i.e. the distribution of the time they spend on shore or on ice, may be influenced by a large number of extrinsic factors such as season, time of day and weather, as well as factors related to the animal's internal state. In this study we used a time-lapse video system at a haulout site, and satellite relay data loggers attached to 11 individual seals to monitor haulout pattern of grey seals Halichoerus grypus in the Baltic Sea during summer and early winter from 1989 through 1996. Time of day had the greatest influence on haulout patterns with the maximum numbers of seals ashore at night. Season and habitat specific characteristics also had important effects on haulout pattern. We suggest that diel changes in prey behaviour and distribution account for the nocturnal haulout pattern observed. The size of the population of grey seals in the Baltic Sea has been estimated by the number of seals ashore. Our results demonstrate the possibility of improving future estimates using a correction based on time of day.
Sex and total weight were recorded in 215 wild reindeer Rangifer tarandus tarandus foetuses from six ranges evaluated as good, medium, and poor based on maternal weights. The proportions of males per 100 females in the good, medium and poor ranges were 76, 112 and 100, respectively, and 94 overall. None of these ratios were statistically different from a 50:50 sex distribution. Examination of individual year and weight classes within areas revealed no difference in foetus sex ratio from a 50:50 ratio. Male and female foetus mean weight differences varied between 28 and 216 g within areas when measured in February and March. None of these differences were significant. Male foetus weights were significantly higher than female weights in April in a pooled sample from the good ranges. Although the sample size is too small for a conclusive statement, the data do not support the Trivers & Willard hypothesis that females should produce more male offspring when resources are abundant.
Controlled experiments were undertaken to examine the quality of the cereal aphid Rhopalosiphum padi as a food source for newly hatched grey partridge Perdix perdix chicks. Growth and flight feather development were measured on chicks fed on three different diets: aphid, grasshoppers, and a mix of the two. Growth and development of flight feathers differed according to diet in the following order: mix > grasshoppers > R. padi. A diet consisting solely of grasshoppers provided sufficient nourishment to partridge chicks but a diet consisting solely of aphids provided poor nourishment. Chicks benefitted from eating R. padi as a supplement to grasshoppers. Our results help to explain why some earlier studies reported a positive correlation between chick survival and cereal aphid density, while others did not.