Weight-related renesting in capercaillie Tetrao urogallus

Abstract

In a population study during 1979-1988 at Varaldskogen in southeastern Norway, 234 capercaillie Tetrao urogallus nests and broods were classified as first nests or renests. Of the females that had their first nest depredated, 9-87% (mean 36%) renested. Over a 6-year period, autumn brood production increased from 30 to 38% due to renesting. Renesting is physically demanding for the females; the eggs in renests are fewer and smaller, and the females take more and longer recesses than when incubating first nests. All the females incubated their first nests till the eggs hatched or the nest was depredated. Two of the renesting females took more and longer recesses until they gave up their nests. The ability to renest seems to be weight-related, as yearling females, which weigh less than adult females, did not renest, and the weight of adult females on leks was highest in the two years when most renesting occurred. The female will renest if the nest is depredated during the first three days of incubation. Each of the following 19 days, all years combined, a mean of 26% of females who lost their nests renested. Capercaillie renesting was related to the vole cycle; it was highest in the year before the small rodents peaked and decreased through the vole crash and the year after.