times of year, while minimizing the potential damaging effects of management
activities on breeding birds. On wet grasslands hydrology is also important in
influencing use by wildfowl and waders.
The most important factors influencing bird use on grasslands are usually the
height and structure of the sward, and the quantity of litter and bare ground. All
these aspects can be manipulated by management, as can vegetation composi-
tion. Vegetation composition can itself influence sward structure, and may also
directly influence food supply, for example, by providing suitable seeds or palat-
able grass species.
Vegetation height and structure affect the suitability of nest-sites, abundance
and accessibility of prey, and the ability of birds to detect predators (e.g. see review
by Vickery et al. 2001). Structure can be difficult to define and measure, but gen-
erally refers to variation in density and height (see Chapter 11). It is useful to dis-
tinguish between fine-scale variation in structure over tens of centimeters (often
referred to as “tussockiness”) and coarse scale variation (over tens of metres or
more). The availability of litter and bare ground can also influence conditions for
some birds. Some species, such as Henslow’s Sparrow Ammodramus henslowii,
require dense litter for nesting, while others, such as Stone Curlew Burhinus
oedicnemus, require bare or sparsely vegetated ground (Green et al. 2000). Bare
ground may also increase access for birds to soil invertebrates (Perkins et al.
2000) and surface-living arthropod prey such as beetles, while a dense litter layer
will reduce it. In general, variation in sward conditions will increase the likeli-
hood of suitable conditions for nesting or feeding being present somewhere in
the area.
Scattered scrub and trees can increase the numbers of bird species using a
grassland, mainly by providing nest-sites and song posts for more generalist
species, rather than grassland specialists. They may also provide nest-sites and
look-out posts for predatory birds and thereby reduce the breeding success or
survival of grassland species (e.g. Green et al. 1990a).
14.5.2Effects of cutting and burning on sward condition
Cutting and burning can both remove all or most of the above-ground vegetation
at once. Uniformity of vegetation removal encourages uniformity in subsequent
vegetation composition, height, and structure. The sudden removal of vegetation
is particularly damaging to invertebrates and small mammals, and this might
affect the suitability of grassland to birds that feed on them. The lack of litter and
tussocks in regularly cut or burnt grasslands will further reduce their suitability for
small mammals. Cutting tends to leave more litter than burning. Burning can
therefore be more suitable for birds requiring bare ground, such as Upland
338 |Habitat management