This study investigated whether predator control is an effective strategy for enhancing bird populations. A systematic review was conducted to determine the impact of predator removal on four measurable responses in birds: breeding performance (hatching success and fledging success) and population size (breeding and post breeding). A meta-analysis was used to summarize results from 83 predator removal studies from six continents. Finally, an investigation was conducted into whether characteristics of the prey, predator species, location, and study methodology explained heterogeneity in effect sizes. Results revealed that removing predators increased hatching success, fledging success, and breeding populations. Removing all predator species achieved a significantly larger increase in breeding population than removing only a subset. Post breeding population size was not improved on islands, or overall, but did increase on mainlands. Heterogeneity in effect sizes for the four population parameters was not explained by whether predators were native or introduced; prey were declining, migratory, or game species; or by the study methodology. Effect sizes for fledging success were smaller for ground-nesting birds than those that nest elsewhere, but the difference was not significant. In conclusion, current evidence indicates that predator removal is an effective strategy for the conservation of vulnerable bird populations. Nevertheless, the ethical and practical problems associated with predator removal may lead managers to favour alternative, nonlethal solutions.
Smith, R.K., Pullin, A.S., Stewart, G.B. & Sutherland, W.J. 2010, Is predator control an effective strategy for enhancing bird populations? CEE review 08-001 (SR38). Environmental Evidence:
This paper seeks to understand the impact of gamekeeping and predator control on gamebirds and other wildlife. Indeed, gamekeeping and predator control was widespread across Britain in the 19th century, meaning that many now common predators (e.g. crows and magpies) were comparatively rare. Similar trends can be seen with other animals such as foxes.
An understanding of this formerly widespread predator control is crucial if we are to restore some of today’s vulnerable and declining birds. The Upland Predation Experiment at Otterburn was designed to explore this. Grouse moors were used as the site of experiment as at present they are the only location at which predator control is practised extensively to support wild game shooting.
Tapper, S.C. 2010, Waders on the Fringe. Why Nationally Scarce Waders Flourish on Grouse Moors. Game & Wildlife Conservation Trust, Fordingbridge, Hampshire
This study investigated whether predator reduction with habitat management can improve songbird nest success. 11 years of nest data from 6 songbird species on 3 lowland farms was analysed. The different game management regimes on the farms enabled researchers to test the hypotheses that systematic predator reduction (mammals and corvids) and sporadic corvid reduction improve nest success in songbirds. A positive effect of systematic predator reduction was detected on common blackbird (Turdus merula), common chaffinch (Fringilla coelebs), dunnock (Prunella modularis ), song thrush (T. philomelos ), and yellowhammer (Emberiza citrinella) but not on common whitethroat (Sylvia communis ). For the 5 species that demonstrated an effect, systematic predator reduction improved the odds of nests surviving a day within the nest cycle by a factor of between 1.59 and 1.89. The extent to which predator reduction might influence populations may depend on mechanisms such as re‐nesting compensation and overwinter mortality. Where habitat management is in place to assist threatened songbirds, intensive, systematic nest predator reduction may provide a useful conservation tool for improvement of nest success.
White, P.J.C., Stoate, C., Szczur, J., & Norris, K.J, 2014, Predator reduction with habitat management can improve songbird nest success, The Journal of Wildlife Management 78.3: 402-412
This study investigated the importance of climatic and environmental change in a population of a multi-brooded ground nesting passerine (woodlark Lullula arborea) over 35 years. The results revealed that woodlarks had greater nest success when rainfall was low and temperature high. When evaluating the effects of weather on population trajectory, it is clear that the effects were minor compared to the effect of nest predation. In this manner, climate change does not provide an explanation for the population decrease over the last 35 years.
Wright, Lucy J., et al. 2009, Importance of climatic and environmental change in the demography of a multi-brooded passerine, the woodlark Lullula arborea, Journal of Animal Ecology 78.6: 1191-1202.
This study investigated the relative importance of different wader chick predators. It used automatic radio tracking stations (ARTS) to constantly record the signals and predation timing of 179 radiotagged Lapwing Vanellus chicks. This was combined with manual telemetry, information from predated remains, and site-level Fox, mustelid and avian predator activity monitoring. The time of predation for 60% of the 155 chicks that were predated was determined. Daytime chick predation accounted for a larger number of predation events, but nocturnal predation was more intensive in terms of predation likelihood per hour. Mammalian predation during both day and night had a larger impact on chick survival than did avian predation. Raptors were primarily responsible for predation by birds and Foxes for predation by mammals, with Foxes also having a larger influence on daily chick predation rates than other predators. Chick predation increased seasonally, implying that earlier-hatching breeding attempts are more likely to be successful. Higher Fox, raptor and mustelid activity resulted in higher proportions of chicks being predated by those predators, so quantifying the activity of those three predator groups on a site could be a quicker alternative to studying chicks when investigating which predator species to target with site-specific predation management.
Mason, L. R., Smart, J. and Drewitt, A. L. (2017), Tracking day and night provides insights into the relative importance of different wader chick predators, Ibis. doi: 10.1111/ibi.12523