1.3. Food availability – a nutritional bottleneck for pheasants in spring?

Pheasants are omnivorous and opportunistic feeders and tend to consume energy rich foods (Cramp & Simmons 1980, Johnsgard 1999). In Britain, they feed predominantly in agricultural habitats (Robertson 1997, Hoodless et al. 2001) which have been subject to increasingly intensive management over the past few decades (Potts 1980, Potts 1991). This has resulted in the decline in number of several seed-eating farmland bird species during the last 30 years (Tucker & Heath 1994, Fuller et al. 1995, Campbell et al. 1997, Chamberlain & Fuller 2000, Chamberlain et al. 2000). Reduced availability of weed seeds and cereal grains during winter has been cited as a probable cause of some of these declines (Evans 1996, Stoate 1996, Campbell et al. 1997, Boatman & Stoate 1999). Several important changes in land use and practice have caused this reduction in seed availability. These include the switch from spring to autumn-sown cropping, increased herbicide inputs and use of more efficient machinery resulting in less over-winter stubble, fewer broadleaved weeds and less grain spilt during harvest (Wilson et al. 1995, O’Connor & Shrubb 1986). Consequently, cereal fields now contain low densities of waste grains and seeds, which are an important component of pheasant diet in spring (Pulliainen 1966, Stromborg 1979, Hoodless et al. 2001)

Birds must store food to fuel periods when they cannot feed due to the necessary performance of other tasks (Cuthill & Houston 1997). During the nesting period the opportunity for gamebirds to feed is not only greatly reduced, but nutritional requirements actually increase above maintenance levels (Wise 1994). Laying hens must therefore accumulate extra fat before nesting. Fat reserves of pheasants are at their highest levels in the pre-breeding period (Anderson 1972). Breitenbach and Meyer (1959) demonstrated that healthy penned pheasants may lose 80% of their body fat during first 20 days of incubation.

It is possible that released birds cannot accumulate sufficient fat reserves when their primary food source is removed at the end of the shooting season. These reduced fat reserves could occur because of one or a combination of three factors: reduced competence at finding natural foods, a poorly developed digestive system, or low availability of energy rich foods on intensively managed modern farmland. In winter, it has been shown that supplementary feeding can maintain or improve body condition in a number of gamebird species including pheasants (Bogenschutz et al. 1995), bobwhite quail (Colinus virginianus) (Robel 1972, Doerr 1988) and black grouse (Tetrao tetrix) (Valkeajärvi & Ijäs 1989). However, little research has been published on the effects supplementary feeding or food limitation on reproductive success of pheasants or other game species, which is surprising considering food supply often limits some aspects of reproduction and occasionally survival in birds (Martin 1987). There is evidence however that egg quality and brood size in some grouse species are related to maternal nutrition (Moss et al. 1975, Beckerton & Middleton 1982, Moss & Watson 1984).