Common pheasant
Negative impacts on other birds

There are a number of negative effects of common pheasants on other game birds, including: nest parasitism, disease, aggression, and competition for resources. Nest parasitism, or brood parasitism, is common in pheasants because of their propensity to nest near other birds and the fact that nesting requirements are similar to those of other prairie birds and waterfowl that inhabit the same areas. This phenomenon has been observed in grey partridges; prairie chickens; several types of duck, rail, grouse, turkeys, and others. Effects of nest parasitism may include abandonment of nests with a high proportion of foreign eggs, lower hatching rates, and lower numbers of eggs laid by the host species. Pheasant eggs also have a shorter incubation time than many of their nestmates, which may result in the individual watching over the nest to abandon her own eggs after the pheasants hatch, thinking that the remaining eggs are not viable. Pheasants raised in other species' nests often imprint on their caretaker, which may result in them adopting atypical behaviour for their species. This is sometimes the cause of hybridisation of species as pheasants adopt the mating behaviour of their nest's host species.

Pheasants often compete with other native birds for resources. Studies have shown that they can lead to decreased populations of bobwhites and partridges due to habitat and food competition. Insects are a valuable food source for both pheasants and partridges and competition may lead to decreased populations of partridges. Pheasants may also introduce disease, such as blackhead, to native populations. While pheasants tolerate the infection well, other birds such as ruffed grouse, chukar, and grey partridge are highly susceptible. Pheasants also have a tendency to harass or kill other birds. One study noted that in pheasant vs. prairie chicken interactions, the pheasants were victorious 78% of the time.
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