AVIS-IBIS

Birds of Indian Subcontinent

Extraordinary Clutch Size and Hatching Asynchrony of a Neotropical Parrot

Publication Type:Journal Article
Year of Publication:1991
Authors:Beissinger, SR, Waltman, JR
Journal:The Auk
Volume:108
Issue:4
Date Published:1991
ISBN Number:00048038
Keywords:Forpus, Forpus passerinus, Psittacidae, Venezuela
Abstract:We studied the nesting biology of the Green-rumped Parrotlet (Forpus passerinus) in the llanos of Venezuela. Clutch size averaged 7 eggs (range: 5-10), and eggs were typically laid daily or every other day over 7-16 days (x̄ = 10). Incubation began with the first egg. Clutches hatched over 2-14 days (x̄ = 8.6) and fledged over 4-17 days (x̄ = 9.7). An average of 5.7 chicks hatched (range: 2-10) and 4.7 chicks fledged (range: 1-8) per successful nest. The number of young fledging increased slightly with clutch size, but parents that hatched more eggs were able to fledge significantly more young. Chicks fledged at 28-35 days of age, and chicks that hatched later and in nests with larger broods took significantly longer to fledge. Hatching success was significantly lower for last eggs in large clutches than for eggs laid earlier or in smaller clutches. However, fertility and volume of last eggs were similar to other eggs. Fledging success was uniformly high for nestlings in small broods, declined slightly for the last two chicks in medium sized broods, and declined sharply for the last two nestlings in large broods. Last-hatched and penultimately hatched chicks were found dead with empty crops significantly more often than earlier-hatched chicks, which implies death by starvation. We evaluated these results in relation to current hypotheses for the evolution of clutch size in tropical birds and the causes of hatching asynchrony. We propose the limited breeding-opportunities hypothesis to explain both the large clutch size and hatching asynchrony in F. passerinus. When opportunities to nest are limited through intra- or interspecific competition, females might be expected to invest heavily in reproductive effort and guard their clutches from nest-site takeovers. This could lead to large clutches, incubation beginning with the first egg, and a large hatching interval.
URL:http://www.jstor.org/stable/4088315
Short Title:The Auk
Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith