Action Synopsis: Bird Conservation About Actions

Reduce adverse habitat alterations by excluding problematic terrestrial species

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Three studies from the USA and the UK found higher numbers of certain songbird species and a higher species richness in these groups when deer were excluded from forests. Intermediate canopy-nesting species in the USA and common nightingales Luscinia macrorhynchos in the UK were the species to benefit.
  • A study from Hawaii found mixed effects of grazer exclusion, with some species showing population increases, some declines and other different long- and short-term trends.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated study in four hardwood forest sites in Pennsylvania, USA, between 1980 and 1991 (deCaslesta 1994) found higher species richness and abundances of intermediate canopy-nesting songbirds in plots with lower densities of white-tailed deer Odocoileus virginianus across sixteen experimental plots (deer density of 3.7 deer/km2: averages of 17.5 individuals and 11 intermediate canopy-nesting species in each plot; 7.9 deer/km2: 16 individuals and 11.5 intermediate canopy-nesting species; 14.9 deer/km2: averages of 13 individuals and seven ICN species; 24.9 deer/km2: averages of 10.5 individuals and 7.5 intermediate canopy-nesting species).  Plots were 13 or 26 ha and contained between one and four deer. There were no changes in either species richness or abundance of ground-nesting or upper canopy-nesting species. Threshold densities for songbirds not found with high deer densities (eastern wood pewee Contopus virens, indigo bunting Passerina cyanea, least flycatcher Empidonax minimus, yellow-billed cuckoo Coccyzus americanus, cerulean warbler Dendroica cerulea, eastern phoebe Sayornis phoebe and American robin Turdus migratorius) appeared to be between 7.9 and 14.9 deer/km2.

    Study and other actions tested
  2. A replicated, controlled study in northern Virginia, USA (McShea & Rappole 2000) found significantly higher numbers of 16 species of ground and intermediate canopy-dwelling songbirds in four 4 ha plots of deciduous forest with deer excluded between 1990 and 1998, compared to five control plots. However, there was no corresponding increase in bird diversity as species were gained and lost as understory vegetation developed. There was also no significant difference in the number of resident birds (eight songbird species and one woodpecker) caught.

    Study and other actions tested
  3. A study in two koa Acacia koa forests in northern Hawaii, USA (Camp et al. 2010), found that all seven native birds recorded in an area of open forest from which feral grazers (cows and pigs) had been excluded showed long-term population stability or growth. However, all but two showed short-term declines. In a closed forest from which grazers were excluded, only two species showed an increase, with the rest either stable or declining. Birds were monitored between 1987 and 2007 in the open forest and 1999 and 2007 in the closed forest. This study is also discussed in ‘Habitat restoration and creation – Forest restoration’.

    Study and other actions tested
  4. A replicated and controlled paired study in southeast England (Holt et al. 2010) found a significantly higher density of common nightingale Luscinia megarhynchos territories (monitored in 2000-8) in a coppiced woodland from which deer were excluded between 1999 and 2003, compared to control plots protected by an easily-breached brushwood fence (0.60 territories/ha in eight exclusion plots vs. 0.04 territories/ha in eight controls). The proportion of territories in exclusion plots also increased, from 0% in 2000 to 70-80% in 2005-7. A total of 48 territories were mapped. Native roe deer Capreolus capreolus and introduced fallow deer Dama dama and Revves’ muntjac Muntiacus reevesi were excluded by erecting 1.8 m steel fences. The authors argue that differences are due to the area of optimal-age coppice (3-8 year old) within plots.

    Study and other actions tested
Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.


Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Bird Conservation

This Action forms part of the Action Synopsis:

Bird Conservation
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

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