Breeding Biology and Natural History of the Slate-throated Whitestart in Venezuela

—We provide details on the breeding biology of the Slate-throated Whitestart (Myioborus miniatus) from 126 nests found during seven breeding seasons, 2002–2008, at Yacambú National Park, Venezuela. Nesting activity peaked in late April and May. Only the female built the nest and incubated the eggs. Males rarely visited the nest during these stages. Mean clutch size (2.1 6 0.04 eggs, n 5 93) was the smallest recorded for the Slate-throated Whitestart. Incubation and nestling period lengths were 15.3 6 0.31 (n 5 21) and 10.8 6 0.24 (n 5 7) days, respectively. Attentiveness (% of time on the nest) during incubation (59 6 1.6%, n 5 52) was similar to other tropical warblers and much lower than northern relatives. This caused a relatively low egg temperature (34.40 6 0.33u C, n 5 6 nests, 20 days) compared with north temperate birds. Both parents fed nestlings and increased their provisioning rates with nestling age. Growth rate based on nestling mass (k 5 0.521 6 0.015) was faster than for other tropical passerines but slower than northern relatives. Predation was the main cause of nesting failure and rate of predation increased with age of the nest. An estimated 15% of nests were successful based on an overall Mayfield daily predation rate of 0.053 6 0.007. This study confirms a strong latitudinal variation in life history traits of warblers. Received 17 September 2009. Accepted 12 March 2010. New World wood warblers (Parulidae) are a small-sized and mostly insectivorous group of birds. Much work has been done on north temperate species, but resident tropical warblers are relatively poorly studied (but see Skutch 1945, 1954; Greeney et al. 2008; Cox and Martin 2009; Morales-Rozo et al. 2009). One of the most broadly distributed genera of this family is Myioborus, which consists of 12 species (Sibley and Monroe 1990, Curson et al. 1994, Ridgely and Tudor 1994). The most widespread species of the genus is the Slate-throated Whitestart (M. miniatus) which is a resident of mountain ranges between 700 and 2,500 m elevation in humid and wet forests (Ridgely and Tudor 1994). It occurs from Mexico to southern Bolivia, and unconfirmed data extend its distribution to northern Argentina (Di Giacomo 1995). It also is vagrant in southern Arizona, New Mexico, and west Texas (Dunn and Garrett 1997). However, the most northern breeding record is in the Sierra Madre Oriental, Mexico (McCormack et al. 2005). Slate-throated Whitestart populations are not threatened anywhere within their range and tolerate nesting in disturbed areas (Collins and Ryan 1994, Curson et al. 1994, Mumme 2010). For these reasons, the species is evaluated as one of Least Concern (IUCN 2009). The wide distribution of this species, which is almost equal to that of the entire genus, makes the Slate-throated Whitestart an interesting species for examining geographical variation. The Slatethroated Whitestart has great plumage and genetic variability along its range (Pérez–Emán 2005). The 12 subspecies recognized show a cline in belly colors from red to orange and yellow from North to Central and South America (Curson et al. 1994). Yet, intraspecific and interspecific comparisons in life-history traits of Myioborus are scarce (Skutch 1945, 1954; Collins and Ryan 1994; Mumme 2010). M. m. ballux is the most common race in the Andes of Venezuela, Colombia, and part of Ecuador. Genetic information for our study site (Yacambú National Park, Venezuela) is lacking, but geographical proximity to Cubiro as well as the occurrence of some slight orange in the breast suggests M. m. ballux is also the race occurring in Yacambú (Phelps and Phelps 1950; J. L. PérezEmán, pers. comm.). Our objective is to provide new information on the breeding biology of the Slate-throated Whitestart in a montane forest in northwest Venezuela. We compare our results with life-history traits recorded for other warblers, especially other Myioborus species.