Clutch size in eastern phoebes (Sayornis phoebe). I. The cost of nest building

Abstract

Eastern phoebes (Sayornis phoebe) may build new nests or repair previously built ones. New nests may be of two types: statant (built on supporting ledges) or adherent (plastered to a vertical surface). Repaired nests are statant. Previous workers compared phoebes building new nests to those repairing old nests and found that new nests require more time and effort to build. Similarly, previous workers found that adherent nests took more time and effort to build than statant nests. At the same time, these workers noted that smaller clutches were laid in new and adherent nests than in repaired and statant nests and concluded that the reduction in clutch size was the result of building the former types of nest. This implies that an increase in the demands on parental time and energy just before egg laying can decrease reproductive output proximally. However, the statistical support for this conclusion was weak, and our reanalysis of the previously reported data does not support it. In addition, previous workers used the terms statant and adherent inconsistently. We advise that nest types be carefully defined according to the expected effect of nest type on the bird's behaviour, not just according to the appearance of the nest. We found that building new nests took longer than repairing old ones. However, we failed to find a difference in the time required to build adherent and statant nests. Furthermore, clutch size was apparently unrelated to the type of nest built. We found no relationship of clutch size to female age or clutch initiation date. The type of nest built for the first clutch size of the season also was not related to the probability that there would be a second clutch, the size of the second clutch, or the interval between clutches. More research is required to show conclusively that increased demands on time or energy just before egg laying can reduce the clutch size of small passerines.