Spatial and temporal variation in breeding parameters of two south‐temperate populations of House Wrens

FERNÁNDEZ, GUSTAVO J.; CARRO, MARIANA E.; LLAMBÍAS, PAULO E.

JOURNAL OF FIELD ORNITHOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2020

0273-8570

Studies of variation in breeding parameters are often based on temporal analyses of a singlepopulation. However, to differentiate between the effects of regional and local factors, neighboring populations withlimited interpopulational dispersal need to be compared.We studied two nearby (< 5 km apart) populations of HouseWrens (Troglodytes aedon bonariae) at two ranches (Los Zorzales, 10 years; La Esperanza, 13 years) in south-temperateArgentina to assess the possible effects of regional and local factors on breeding phenology. For each breeding season,we recorded laying dates, clutch sizes, and length of the breeding season, and estimated the reproductive synchrony offirst and second breeding attempts. We examined how these breeding parameters were affected by weather, populationdensity, and rates of nest failure. With favorable temperatures during the pre-reproductive period (September?October), wrens in both populations initiated first breeding attempts earlier. However, ordinal laying dates were alsoaffected by local factors, with wrens at Los Zorzales initiating breeding attempts earlier than those at La Esperanza. Wefound a spatial correlation in clutch sizes between populations for the 2007?2012 breeding seasons, but clutch sizes offirst and second nesting attempts showed low variability. Reproductive synchrony of first nesting attempts variedamong years, suggesting an effect of regional factors. However, we detected no synchronization between populationsand were unable to identify environmental variables that explained the temporal variation. Ordinal laying dates ofsecond clutches were strongly correlated with the ordinal laying dates of first clutches. We also found that the length ofbreeding seasons was longer when daily nest mortality rates were lower. Although environmental factors seemed toaffect the decision of when to start breeding, pairs with successful first nesting attempts were more likely to initiatesecond nests, thus affecting the length of the breeding season. The spatial variation and temporal variation of thebreeding parameters of House Wrens in our study provide evidence of marked plasticity in their breeding decisionsand allowed us to identify local and regional environmental factors related to this variation.