Teste do efeito de borda na predação de ninhos naturais e artificiais no Cerrado

Abstract

ABSTRACT. A test of the edge effect on predation of natural and artificial bird nests in the Cerrado. The Cerrado is still one of the most important ecosystems in Brazil, even though more than 50% of its area has been altered or converted to pastureland and plantations. Despite its intense degradation, few ecological processes that might affect its biodiversity have been evaluated. The goal of this study was to test the edge effect on the predation rates at natural and artificial nests, at the Ecological Station of Águas Emendadas, Federal District, Brazil. Natural nests were found and monitored every three to four days from September to December of 2004 in the interior and at the edge of the reserve.Artificial nests were placed at four distances from the edge (0, 500, 1000 and 2000 m) in three spatial replicates in September and again in December of 2004. Each nest received one Japanese Quail and one plasticine egg and was monitored every five days, for 15 days. There was no difference between the rates of predation either in the natural nests or in the artificial nests between treatments. For one bird species, Elaenia chiriquensis (Lawrence, 1865), Tyrannidae, daily survival rates in the incubation and in the hatchling period had opposite values between the edge and the interior.Marks on plasticine eggs suggest that birds are the main predators. Estimates of the abundance of two potential nest predators, Cyanocorax cristatellus (Temminck, 1823), Corvidae and Canis familiaris (Linnaeus, 1758), Canidae, revealed no relationship with distance to the edge, nor with predation rates. Brood parasitism of natural nests was similar between the interior (0%) and the edge (3.8% of the nests). The results described here do not support the edge effect hypothesis for nest predation rates on either natural or artificial nests, nor for brood parasitism rates.

Predation on artificial nests in open habitats of central Brazil: effects of time and egg size

“…A previous study showed similar tendency for large eggs (quail eggs; França & Marini 2009a). Surprisingly, studies of natural nests in the same region found declining nest survival rates as the breeding season progressed (Borges & Marini 2010, Santos 2008.…”

“…In contrast, in some areas in the Cerrado, birds were the main predators (França et al 2009). Overall, predation in the Cerrado habitats tended to increase throughout the reproductive period (Borges & Marini 2010), decrease during nest development (França & Marini 2009b), and differ between habitats and microhabitats (França & Marini 2009a, Borges & Marini 2010. These studies show the importance of predation for population dynamics of neotropical birds and so experiments with artificial nests may be important to understand spatial and temporal patterns of reproductive success.…”

“…Small birds, such as the Black-capped Chickadee (Parus atricapillus) also seem to be unable to consume quail eggs (Maier & DeGraaf 2001). Because birds seem to be important nest predators in the Cerrado (França & Marini 2009a, França et al 2009), it would be important to determine if some small Cerrado birds cannot consume large eggs which might explain the difference in predation rates between artificial and natural nests.…”

“…The few neotropical studies with artificial nests or both natural and artificial nests were conducted in closed forested areas (Roper 2000, Robinson et al 2005, Alvarez & Galetti 2007, where birds were not an important set of predators, or in open areas of Cerrado , but not controlling for egg sizes (França & Marini 2009a). As with natural nests, predation risk was influenced by habitat or nest characteristics (França & Marini 2009a, Chiarello et al 2008, Boyle 2008, Alvarez & Galetti 2007, Robinson et al 2005.…”

“…As with natural nests, predation risk was influenced by habitat or nest characteristics (França & Marini 2009a, Chiarello et al 2008, Boyle 2008, Alvarez & Galetti 2007, Robinson et al 2005. Experiments with artificial nests in the neotropics detect spatial and temporal variation in nest predation risk, yet how these effects resemble those observed for natural nests are unknown.…”