Projects - The Hen Harrier as an Indicator Species
More direct uses of raptors as indicators are rare, beyond the simple examples such as presence and abundance of prey species in an area from raptor diet analysis or presence of raptor corpses below power cables or at windfarm sites.
The Problem Of Farmland Bird Decline
There has been considerable concern in Europe that decline in survival resulting from reduced overwinter food supplies on modern farms is one of the factors inducing very substantial reductions in populations of farmland birds in recent decades (e.g. Newton 2004). The arable weeds on which many farmland birds depend on for seed and leaf foods, and as hosts for the insects they eat, have largely been brought under control by modern farming methods. Certain arable weeds known to have been important to birds for their seeds have virtually disappeared in Britain, for example Charlock Sinapsis arvensis and the hempnettles Galeopsis spp.. Also, cereal grain wastage at harvest is much reduced due to improved efficiency in mechanisation. Recent trials in the UK have shown that weeds can be further reduced in the GM varieties of important crops (Firbank et al. 2003).
Harnessing Harriers To Monitor Farmland Bird Diets
The monitoring of diets of farmland birds has been severely limited due to the bias and technical difficulties associated with methods such as observation and faecal analysis. Information on diet for individual bird species is often restricted to dated and geographically extremely limited studies. The recent thrust in work on farmland birds in Europe has been on habitat use, without detailed underlying analysis of the foods relied on by individual species and in different regions. Agri-environment schemes have in the past been applied without adequate research, and have not had the hoped-for impact (Chamberlain 2004).
Recent work on Hen Harriers (e.g. Clarke et al. 1997, Clarke et al. 2003) has shown that immigrant Hen Harriers Circus cyaneus wintering in lowland England forage mainly for small birds – larks Alaudidae, accentors Prunellidae, finches Carduelidae and buntings Emberizidae. These are mainly seedeaters in winter, and seeds in their upper digestive tracts at time of capture are ingested by harriers and subsequently egested in pellets. Large samples of pellets can be collected at harrier communal roosts, and sub-samples of those pellets containing only one species of seedeater have been examined for seeds to obtain species specific results. These showed a general dependence on the seeds of a limited range of arable weeds, and both interspecific differences in seed diets in study areas and intraspecific differences between study areas (Clarke et al. 2003).
Dealing With Bias In Results
Some foods eaten by farmland birds may be less readily reflected in the contents of harrier pellets than weed seeds. For example, although cereal grains do come through in the great majority of harrier pellets with the remains of known cereal specialists such as Yellowhammers Emberiza citrinella, grain abundance relative to weed seeds may be reduced by susceptibility of cereal to pre-digestion in the crops of small passerines. Because of the known importance of cereal grain as a food for farmland birds in some cereal fields (Robinson 2004), this aspect will need careful study. Preliminary trials on captive harriers indicate that methods to speed up the meal to pellet interval greatly improve the output of seeds in pellets, but it still appears to fall short of the quality of seed output in pellets from wild harriers. More work is required on this.
Modeling Habitat Use By Raptor And Prey Based On Lower Trophic Level Resources
The University of Nottingham in conjunction with the Hawk and Owl Trust have initiated a 3-year postgraduate study to use a network of harrier roosts routinely surveyed in eastern and southern England by the national Hen Harrier Winter Roost Survey to develop a GIS-based model of habitat use by both harriers and their prey, expressing the trophic links between habitat, farmland birds and harriers based on knowledge of the foods of prey. The aims are to assist with:
The Problem Of Farmland Bird Decline
There has been considerable concern in Europe that decline in survival resulting from reduced overwinter food supplies on modern farms is one of the factors inducing very substantial reductions in populations of farmland birds in recent decades (e.g. Newton 2004). The arable weeds on which many farmland birds depend on for seed and leaf foods, and as hosts for the insects they eat, have largely been brought under control by modern farming methods. Certain arable weeds known to have been important to birds for their seeds have virtually disappeared in Britain, for example Charlock Sinapsis arvensis and the hempnettles Galeopsis spp.. Also, cereal grain wastage at harvest is much reduced due to improved efficiency in mechanisation. Recent trials in the UK have shown that weeds can be further reduced in the GM varieties of important crops (Firbank et al. 2003).
Harnessing Harriers To Monitor Farmland Bird Diets
The monitoring of diets of farmland birds has been severely limited due to the bias and technical difficulties associated with methods such as observation and faecal analysis. Information on diet for individual bird species is often restricted to dated and geographically extremely limited studies. The recent thrust in work on farmland birds in Europe has been on habitat use, without detailed underlying analysis of the foods relied on by individual species and in different regions. Agri-
Recent work on Hen Harriers (e.g. Clarke et al. 1997, Clarke et al. 2003) has shown that immigrant Hen Harriers Circus cyaneus wintering in lowland England forage mainly for small birds – larks Alaudidae, accentors Prunellidae, finches Carduelidae and buntings Emberizidae. These are mainly seedeaters in winter, and seeds in their upper digestive tracts at time of capture are ingested by harriers and subsequently egested in pellets. Large samples of pellets can be collected at harrier communal roosts, and sub-
Dealing With Bias In Results
Some foods eaten by farmland birds may be less readily reflected in the contents of harrier pellets than weed seeds. For example, although cereal grains do come through in the great majority of harrier pellets with the remains of known cereal specialists such as Yellowhammers Emberiza citrinella, grain abundance relative to weed seeds may be reduced by susceptibility of cereal to pre-
Modeling Habitat Use By Raptor And Prey Based On Lower Trophic Level Resources
The University of Nottingham in conjunction with the Hawk and Owl Trust have initiated a 3-
1. Predicting and monitoring the effects on biodiversity of changes in cropping mosaics and crop management due to agri-environment schemes or rapid technological changes such as GM
2. Delineating the Special Protection Areas required to be established for listed species (both raptor and prey) by European Union law, and
3. In comparison with breeding season ranging studies and with appropriate input of breeding season parameters into the model, identify marginal breeding habitat for re-colonization by the Hen Harrier, a red-list species in the UK.
Hen Harriers (Circus cyaneus) as Direct Environmental Indicators
The dynamics of raptor population sizes and ranges are widely regarded as barometers of the health of the environment. The classic example of this as a warning mechanism was of course the danger of organochlorines revealed by their accumulation in raptors (especially Peregrine Falcon Falco peregrinus, Sparrowhawk Accipiter nisus and Merlin F. columbarius) in the late 1950s and 1960s.
