Exeptionally large clutches in two birds of prey breeding in nest boxes

OROZCO, P. M.; GRANDE, J. M.

JOURNAL OF RAPTOR RESEARCH

RAPTOR RESEARCH FOUNDATION INC

Lugar: Lawrence, Kansas; Año: 2016 vol. 50 p. 232 - 236

0892-1016

In birds, clutch size can be affected by several factors linked toindividual and territory variability as well as to variability in some abioticfactors. In South America, the Ferruginous Pygmy-Owl (Glaucidium brasilianum) clutchsize usually ranges from two to five eggs although in studies in North America some 7 eggs clutches have been detected. TheAmerican Kestrels (Falcosparverius) clutch size usually ranges from four to sixeggs. In South America all recorded clutchsizes in the late species did not exceed five eggs. Here we present recordsof same season exceptionally large clutches for both speciesbreedingin nest boxes put up for American kestrels in semiarid forest andagricultural lands in La Pampa Province, Central Argentina. From 1998 to 2014, between13 and 104 nest boxes have been monitored yearly with the exception of2004-2005 and 2007-2009 where the boxes were not monitored. In 2014 breedingseason one of the boxes was occupied by Ferruginous Pygmy-owls. This pair laidan exceptional clutch of seven eggs (to our knowledge the largest clutch ever recordedfor the species in South America).Sixnestlings fledged successfully. In the same season, unusually large clutches wererecorded for American Kestrels too, with six clutches of six eggs, threeclutches of seven eggs and one clutch of eight eggs (apparently from two differentlaying events). Hatching never exceeded six individuals in any of theexceptional clutches. In previous seasons breeding parameters in our study areawere similar to those reported in other areas, at least in the case of AmericanKestrels. Therefore, extremely large clutches reported here are probablythe result of an exceptionally good year in food resources for these twospecies.