Exclusion of deer affects responses of birds to woodland regeneration in winter and summer

Abstract

Using an exclosure experiment in managed woodland in eastern England, we examined species and guild responses to vegetation growth and its modification by deer herbivory, contrasting winter and the breeding season over 4 years. Species and guild responses, in terms of seasonal presence recorded by multiple point counts, were examined using generalized linear mixed models. Several guilds or migrant species responded positively to deer exclusion and none responded negatively. The shrub-layer foraging guild was recorded less frequently in older and browsed vegetation, in both winter and spring. Exclusion of deer also increased the occurrence of ground-foraging species in both seasons, although these species showed no strong response to vegetation age. The canopy-foraging guild was unaffected by deer exclusion or vegetation age in either season. There was seasonal variation in the responses of some individual resident species, including a significantly lower occurrence of Eurasian Wren Troglodytes troglodytes and European Robin Erithacus rubecula in browsed vegetation in winter, but no effect of browsing on those species in spring. Ordinations of bird assemblage compositions also revealed seasonal differences in response to gradients of vegetation structure generated by canopy-closure and exclusion of deer. Positive impacts of deer exclusion in winter are probably linked to reduced thermal cover and predator protection afforded by browsed vegetation, whereas species that responded positively in spring were also dependent on a dense understorey for nesting. The effects on birds of vegetation development and its modification by herbivores extend beyond breeding assemblages, with different mechanisms implicated and different species affected in winter

Factors affecting the bird diversity of planted and semi-natural oak forests in Ireland

“…Deer abundance is increasing in Europe (Gill 1990, Ward 2005, Loe et al 2009, Apollonio et al 2010 and they can exert a considerable influence on the vegetation structure of woodlands (Gill & Beardall 2001, Perrin et al 2006, Newson et al 2012) and on ecosystem functioning (Newson et al 2012). Excessive grazing (herbivory in ground and herb layers of vegetation) and browsing (foraging of vegetation in shrub and understorey layers) can impact negatively on woodland habitat complexity by decreasing the cover and suppressing the development of shrubs, climbers, seedlings and saplings, as well as vegetation in the ground and herb layers (Putman et al 1989, Gill & Beardall 2001, Stockton et al 2005, Gill 2006, Holt et al 2013. These impacts (hereon referred to collectively as 'browsing') can have cascading impacts on the biodiversity of birds (Martin & Joron 2003, Allombert et al 2005a, Gill & Fuller 2007, Newson et al 2012) and other taxa (Putman et al 1989, Baines et al 1994, Allombert et al 2005b.…”

Effects of deer on woodland structure revealed through terrestrial laser scanning

“…). Within the UK, high deer densities have been shown to correlate with declines in a number of bird species at both local (Holt, Fuller & Dolman ) and landscape scales (Newson et al . ).…”

“…Our results imply that reduction of deer populations to low levels (c. 1 km −2 ) is the most effective means of directing whole stand structures towards desired states, especially to increase the density of understory foliage. Previous work has shown that deer exclusion benefits birds which forage in the understorey and shrub layer, with no evidence of negative effects on any bird species (Holt et al ., ). On regional scales there is a strong association between deer densities and decline in understorey bird species (Newson et al .…”

Overabundant ungulates in French Sologne? Increasing red deer and wild boar pressure may not threaten woodland birds in mature forest stands

“…In particular, increasing ungulate populations have been considered a strong driver of change in forest bird communities, especially because understory-dependent birds may be threatened (Schley & Roper 2003;Holt, Fuller, & Dolman 2014;Newson, Johnston, Renwick, Baillie, & Fuller 2012). Ungulates negatively affect bird communities either directly by wild boar preying on nests, nestlings or adult birds (Schley & Roper 2003), or indirectly by modifying understory plant species composition and structure through wild boar rooting or deer browsing (Genov & Massei 2004;Heinken, Schmidt, von Oheimb, Kriebitzsch, & Ellenberg 2006;Boulanger et al, 2009).…”