Nest site selection by the endangered black robin increases vulnerability to predation by an invasive bird

Abstract

Few studies have investigated the impacts of established invasive birds on the native threatened avifauna. However, measuring the levels of mortality in native birds from exotic birds can help with management decisions on whether or not such introduced species need to be controlled. The black robin Petroica traversi is an endangered bird endemic to the Chatham Islands of New Zealand. Black robins build cup-like nests either within tree cavities ('cavity' nests) or in the sub-canopy vegetation ('open' nests). Nest predation, most likely by the invasive European starling Sturnus vulgaris, was the largest cause of nest failure in the main population of the black robin on Rangatira Island. Nest predation rate over five breeding seasons was 20.6% in comparison with 7.74% of nests failing because of severe weather events (the second largest cause for nest failure). Cavity nests experienced a significantly higher rate of predation (36.33%) than open nests (10.82%). The greater frequency of open nests (63.5% out of 244 nests monitored) may be a result of higher selection pressure by starlings on cavity nests. Nest height also influenced predation, with predation risk increasing from 4.88% for nests below 1 m to 31.89% for nests above 3 m. Overall, predation on black robin nests decreased chick production in the population by 15.6% annually. For a population of only 220-240 birds, this loss may be limiting continued population growth and we recommend that efforts be made to reduce predation through either the culling of starlings or the installation of nest boxes at the low heights avoided by starlings. bs_bs_banner Animal Conservation. Print ISSN 1367-9430 Starling predation and endangered black robins M. Massaro, M. Stanbury and J. V. Briskie

Nest site characteristics and nest loss of Marsh Grassbird at Zhalong National Nature Reserve, China

“…3 The nest after predation Other studies also reported that predation was one of the most common causes of nest failure (Allen and Peters 2012;Massaro et al 2013;Fondell and Ball 2004). Nests located at sites with thicker litter may be better protected from predators because the thicker litter limits predator access to the nest and provides increased visual obstruction (Fondell and Ball 2004;Neto 2006).…”

How old is this bird? The age distribution under some phase sampling schemes

“…. , [9,10), [10, ∞), and we denote the asymptotic frequency of the age-class starting at age x as f a x , 0 ≤ x ≤ 10. We can then compute f a x as…”

“…This artificially increased reproductive success in combination with our assumption that the fertility and mortality rates are fixed over a long time period, results in an age pyramid whose shape may not be representative of the current population. Given that the current black robin population is restricted to only two small islands and includes fewer than 250 individuals, the species remains endangered [9]. Hence, knowing the age frequency of this population, and the associated fertility and mortality rates, is highly relevant to the future conservation management of this species; this is investigated in more detail in the parallel study 3 .…”

“…Over the next decade (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998), the population was closely monitored, but without human intervention. Nevertheless the population continued to grow rapidly to 197 adults by 1998, but after this period, the population growth slowed considerably and it only reached 239 adults in 2011 [9].…”

New Zealand falcon prey selection may not be driven by preference based on prey nutritional content

“…Conservation-related research, especially on island ecosystems that have been invaded by introduced species (Courchamp et al 2003), typically examines predation on native species by introduced species. In a New Zealand context, a well-supported idea is that native species (often birds, but also reptiles) have not coevolved with (typically) mammalian predators and are prone to falling prey to introduced predators because of a lack of evolved defences (Diamond & Veitch 1981;Towns et al 2001;Wilson 2004;Massaro et al 2012;Stanbury & Briskie 2015). Prior to human arrival c. 1280 AD, New Zealand did not have significant mammalian predators, so this niche was filled by avian predators -one of these being the kārearea.…”