Many animals build extravagant nests that exceed the size required for successful reproduction. Large nests may signal the parenting ability of nest builders suggesting that nests may have a signaling function. In particular, many raptors build very large nests for their body size. We studied nest size in the goshawk Accipiter gentilis, which is a top predator throughout most of the Nearctic. Both males and females build nests, and males provision their females and offspring with food. Nest volume in the goshawk is almost three-fold larger than predicted from their body size. Nest size in the goshawk is highly variable and may reach more than 600 kg for a bird that weighs ca. 1 kg. While 8.5% of nests fell down, smaller nests fell down more often than large nests. There was a hump-shaped relationship between nest volume and female age, with a decline in nest volume late in life, as expected for senescence. Clutch size increased with nest volume. Nest volume increased during 1977-2014 in an accelerating fashion, linked to increasing spring temperature during April, when goshawks build and start reproduction. These findings are consistent with nest size being a reliable signal of parental ability, with large nest size signaling superior parenting ability and senescence, and also indicating climate warming.
Keywords: Accipiter gentilis; Climate change; Extended phenotype; Goshawk; Senescence; Signal.