Artificial nest predation rates vary depending on visibility in the eastern Brazilian Amazon

Abstract

Observational and experimental studies have shown that increased concealment of bird nests reduces nest predation rates. The objective of the present study was to evaluate differences in predation rates between two experimental manipulations of artificial ground nests (i.e., clearing an area around the artificial nest or leaving it as natural as possible), and test whether environmental variables also affected nest predation in an undisturbed area of Amazonian forest in eastern Brazil. A generalized linear model was used to examine the influence of five variables (manipulation type, perpendicular distance from the main trail, total basal area of trees surrounding the nest site, understorey density, and liana quantity) on nest predation rates. Model results, showed that manipulation type was the only variable that significantly affected nest predation rates. Thus, to avoid systematic biases, the influence of nest site manipulation must be taken into consideration when conducting experiments with artificial nests. KEYWORDS: Experimental manipulation, potential biases, quail egg. Taxas de predação em ninhos artificiais variam dependendo da visibilidade na Amazônia Oriental Brasileira RESUMOEstudos de observação e experimentais demonstraram que ninhos de aves menos visíveis apresentam taxas de predação reduzidas. O objetivo do presente estudo foi avaliar diferenças nas taxas de predação entre duas manipulações experimentais de ninhos artificiais no chão (i.e., limpando uma área em torno do ninho artificial ou deixando o mais natural possível), e testar se variáveis ambientais também poderiam afetar as taxas de predação em uma área intacta de floresta amazônica no leste do Brasil. Um modelo generalizado linear foi utilizado para examinar a influência de cinco variáveis (tipo de manipulação, distância perpendicular da trilha principal, área basal total das árvores em volta do local do ninho, densidade de sub-bosque, e quantidade de lianas) sobre as taxas de predação de ninhos. Os resultados do modelo demonstraram que tipo de manipulação foi a única variável que afetou significativamente as taxas de predação de ninhos. Assim, para evitar vieses sistemáticos, a influência da manipulação do local dos ninhos deve ser levada em consideração na realização de experimentos com ninhos artificiais. PALAVRAS-CHAVE: Manipulação experimental, potenciais vieses, ovo de codorna. Nest predation is not only the primary cause of reproductive failure in birds, but is also a major factor that can shape the evolution of avian life histories (Ricklefs 1969;Martin 2002), and drive bird species population dynamics (Clark and Martin 2007). Nest site selection and nest defense are strategies used by birds to reduce nest predation (Martin 1993;Götmark et al. 1995;Boulton et al. 2003). Indeed, according to the nest-concealment hypothesis, nests that are more concealed are less prone to be predated (Ricklefs 1969;Filliater et al. 1994;Weidinger 2002).Nest predation may be also determined by the community of potential predators (Weatherhea...

A different kind of ecological modelling: the use of clay model organisms to explore predator–prey interactions in vertebrates

“…Other variables (distance from trail, understorey density, etc.) did not influence predation rates (Michalski & Norris, ). Even the nest type can have an effect: plasticine eggs in artificial nests mimicking open‐type nests were predated more than were eggs in artificial domed‐type nests (Noske et al ., ).…”