Dense canopy cover over House Wren (Troglodytes aedon) nests increases latency of brood parasitism by Shiny Cowbirds (Molothrus bonariensis)

FIORINI, V.D.; TUERO, D.T.; REBOREDA, J.C.

EMU

CSIRO PUBLISHING

Año: 2012 vol. 112 p. 55 - 59

0158-4197

Obligate brood parasites must find host nests to lay their eggs. The search for a suitable host nest is predicted to be more difficult if it is highly concealed by vegetation (nest concealment hypothesis), and therefore brood parasitism should be less common at concealed nests. We experimentally tested this hypothesis by placing nest-boxes used by House Wrens (Troglodytes aedon) in woodland sites with low and high canopy cover and measuring the frequency (proportion of nests parasitised), latency (days elapsed since laying of the first host egg and parasitism), and intensity (number of parasite eggs in parasitised nests) of parasitism by Shiny Cowbird (Molothrus bonariensis). Frequency and intensity of parasitism did not differ between nests-boxes in sites with low or high canopy cover, but latency of parasitism was shorter in sites with low concealment than in sites with high concealment. Brood parasites that find host nests more quickly have higher reproductive success, while wrens have higher reproductive success when parasites lay their eggs later during the incubation period due to reduced mortality effects on host nestlings. Because woodland degradation is associated with lower canopy cover, host species nesting in degraded woodlands may suffer higher costs of parasitism than those nesting in protected woodlands.