Spruce grouse, a non-gregarious and sparsely distributed forest bird, shows synchronous nesting

Abstract

Hatch dates, densities, age-structure, and production rates were documented for female spruce grouse (Dendragapus canadensis) in Alberta, Ontario, and New Brunswick, Canada, over a total of 17 years during 1970-1990. Objectives of analyses were to measure the magnitude of synchrony of hatch dates at different densities of females in different areas, determine whether synchrony differs between adults and yearlings, determine whether adults might influence the time and synchrony with which yearlings hatch clutches, and determine whether mean production of juveniles into late summer varies across the span of hatch dates. Hatch date synchrony was substantial in all areas: on average, 67% of all clutches each year hatched within 6.5-8.8 days, within areas, similar to that among colonial avian species. The extent of synchrony was not correlated well with female density, in contrast to a general prediction from Darling's hypothesis for colonial species. Synchrony did not differ between yearlings and adults in all areas even though yearlings generally hatched clutches later than adults. Synchrony was not correlated well with an index of the magnitude of interaction between adults and yearlings, suggesting that adults had little if any effect on the timing of reproductive activity of yearlings. In contrast, median hatch dates of yearlings were 1-2 days earlier where adults were experimentally thinned than where adults were common. Production of juveniles into late summer did not vary across the span of hatch dates despite their synchronous temporal distribution, providing no evidence for an immediate adaptive value for synchronous nesting.