Other studies

The role of the Eurasian Sparrowhawk (Accipiter nisus) in the decline of the House Sparrow (Passer domesticus) in Britain

This study investigated the role of the Eurasian Sparrowhawk (Accipiter nisus) in the decline of the House Sparrow (Passer domesticus) in Britain from 1970. Researchers compared the pronounced geographic pattern in the recolonization of Britain by the Eurasian Sparrowhawk (Accipiter nisus) from 1970 onward with the spatiotemporal pattern among House Sparrow (Passer domesticus) populations over the same period, using data on the occurrence of both species at garden feeding stations. The results indicated that House Sparrow numbers were generally stable or increasing prior to recolonization by Eurasian Sparrowhawks but declined continuously afterward. The results therefore suggest that predation by Eurasian Sparrowhawks may be a sufficient explanation for the decline in House Sparrows in Britain.

Fear for the family has negative consequences: indirect effects of nest predators on chick growth in a farmland bird

This study investigated the indirect effects of nest predators and perceived parental fear of predation on chick growth in a farmland bird, the yellowhammer (Emberiza citrinella).

Indeed, the increased management of habitat structure through agricultural intensification results in limited access to food and parents exhibiting a greater perceived risk of predation.

The results revealed that this perceived risk of predation means that adults are likely to reduce their activity in order to avoid disclosing the location of their offspring and thus decrease risk of predation. As a consequence, their ability to provide for the brood was reduced, negatively affecting chick condition and growth.

In areas of low food availability, corvid abundance was associated with reduced chick growth and condition; in areas of higher food availability no association was found indicating that where food resources are abundant, parents can compensate for reductions in provisioning rate when cor- vids are active, with no long-term implications for chicks.

The researchers therefore advise that management should concentrate on improving the quality of foraging habitat by creating mosaics of long and short vegetation, rather than on the control of corvids. This will allow adult birds to compensate for the indirect effects of high corvid abundance by increasing their provisioning effort when nest predation risk is low and thus buffer any long-term consequences for nestlings.

Invertebrate prey availability limits reproductive success but not breeding population size in suburban House Sparrows Passer domesticus

This study investigated whether the lack of invertebrate prey is responsible for the declines of House Sparrow (Passser domesticus) populations across Europe. A replicated supplementary feeding experiment was conducted over two successive breeding seasons. This involved providing daily mealworm sufficient to provide 82% of chick energy requirements of House Sparrow pairs nesting within 50 m of feeders. This was shown to have a large positive impact on the abundance of recently fledged birds (+62%), but only a small positive impact, limited mainly to small colonies, on the overall abundance of territorial males. Colony growth was only weakly related to fledgling abundance in the previous year and did not appear to be constrained by nest-site availability. Therefore, whilst conservation interventions that enhance invertebrate availability may increase reproductive success, they are unlikely to lead to population growth or recovery on their own.

Bayesian hierarchical modelling of continuous non‐negative longitudinal data with a spike at zero: An application to a study of birds visiting gardens in winter

The development of methods for dealing with continuous data with a spike at zero has lagged behind those for overdispersed or zero-inflated count data. We consider longitudinal ecological data corresponding to an annual average of 26 weekly maximum counts of birds, and are hence effectively continuous, bounded below by zero but also with a discrete mass at zero. We develop a Bayesian hierarchical Tweedie regression model that can directly accommodate the excess number of zeros common to this type of data, whilst accounting for both spatial and temporal correlation. Implementation of the model is conducted in a Markov chain Monte Carlo (MCMC) framework, using reversible jump MCMC to explore uncertainty across both parameter and model spaces. This regression modelling framework is very flexible and removes the need to make strong assumptions about mean-variance relationships a priori. It can also directly account for the spike at zero, whilst being easily applicable to other types of data and other model formulations. Whilst a correlative study such as this cannot prove causation, our results suggest that an increase in an avian predator may have led to an overall decrease in the number of one of its prey species visiting garden feeding stations in the United Kingdom. This may reflect a change in behaviour of house sparrows to avoid feeding stations frequented by sparrowhawks, or a reduction in house sparrow population size as a result of sparrowhawk increase.

Perceived predation risk reduces the number of offspring songbirds produce per year

This study investigated the impact of perceived predation risk on reproduction rates. It did so by conducting short term (60 minute) predator playback manipulations on free-living, banded populations of song sparrows. The results revealed that when exposed to the sounds of predation, the number of surviving fledglings decreased by ~24% as a consequence of parent song sparrows reducing the amount of food they provide by 60%. Further, the number of offspring produced per year was reduced by ~54%.

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