Northern bobwhite (Colinus virginianus) COSEWIC status report: chapter 5
Habitat
Habitat requirements
The Northern Bobwhite requires an early successional habitat that can be provided in a variety of vegetation types (Brennan 1999). Minimally it requires an interspersion of grassland, cropland, and brushy cover. In Ontario it is now usually associated with cultivated lands, rather than native prairie fringes. They require grasslands for summer nesting, some feeding and limited roosting, croplands during summer and autumn for feeding, dusting, loafing and some roosting, and dense brushy cover for escape and roosting year round, and for feeding during autumn and winter.
It is also important that the three types of habitat are interspersed adequately so that all three types are available in close proximity. The amounts of each can vary considerably, as long as interspersion is high (Rosene 1969). It is also important that, once minimum interspersion requirements are met, that there be an adequate quantity of habitat. The population that can be expected will vary in the long term as the quantity through time that is available (Guthery 1997).
Trends
The value of agricultural lands has diminished in recent years as field sizes have increased, fencerows have been removed, pesticides and herbicides have depleted food sources and secondarily killed the birds feeding on them, and as brushy cover has been eliminated or increasingly isolated (Brennan 1999).
In Ontario there were originally thousands of hectares of long-grass prairie in the extreme southwest (Lumsden 1987). After settlement by Europeans, the creation of numerous small farms with diverse crops, inefficient harvest methods and large weedy hedgerows greatly enhanced the potential for bobwhites, and resulted in the tremendous population increase. But, through the previous century, the trend has been away from pasture (a 65% decline 1921-1986; and a further 19% decline 1986-1996) and summer fallow (a 44% decline 1931-1986; and a further 76% decline 1986-1996) greatly reduced the potential available habitat for bobwhite (Page and Austen 1994, Statistics Canada 1997). Available natural prairie has been all but eliminated in most places.
Perhaps more serious is the fragmentation of habitat. Bobwhites generally do not move long distances, and as suitable patches of habitat become isolated, there is a greater risk that a local population will be eliminated, with little or no chance of recolonization from other areas; reduced populations will also be slow to recover, and may never recover (Roseberry and Klimstra 1984). Furthermore, in human dominated landscapes, there are burgeoning populations of house cats, raccoons, foxes, coyotes, and skunks, that will be serious mortality agents, making survival even more difficult (Burger et al. 1995, Brennan 1999).
Overall, there has been a great reduction in available habitat in southern Ontario in the past century. Birds are now absent from what appears to be suitable habitat in many places, probably because of the isolation of these places. The main cause of decline in bobwhite populations in Canada has no doubt been this loss and fragmentation of habitat as it has been in many parts of the United States (Brennan 1991, Page and Austen 1994). But, populations have remained small after suffering losses to severe winter weather, because habitat has been fragmented with birds under heavy predation pressure. Adequate winter cover and food may be key to survival in Ontario, and where there is good habitat in sufficient quantity, they have persisted.
Bobwhite habitat is not currently protected in Ontario. Modern agricultural practices and urban development continue to threaten remaining habitat in most areas. However, there are recent encouraging developments that provide renewed optimism for bobwhite and other grassland species in southern Ontario. There is apparently much habitat in southwestern Ontario that appears to be suitable for bobwhites, where there are no remaining birds (Hunter 1990). With enhancement of intervening areas, and maintenance of existing areas, there is reason to believe that habitat can be provided to sustain much larger populations.
Protection/ownership
Much of the appropriate land is in private hands and there is a high degree of interest among landowners in bobwhite. Many are willing to participate in habitat enhancement programs. Walpole Island, managed by the Walpole Island Indian Band, is an important block of habitat, and the people are aware of the situation, and are amenable to maintaining birds there (P. Hunter and R. Ludolph, Pers. Comm., 1999).
Perhaps the most positive outlook for bobwhite and other grassland species evolves from the work of the Lambton Stewardship Council in the long-grass prairie restoration work that they are doing. They have already set out more than half a million plants, have nearly a million more ready to set out, are planning to seed several other areas, have two staff working on restoration and four others collecting and cleaning seed, are growing more than 70 different plants of native grasslands, and are undertaking controlled burns and removal of inappropriate brush to restore and maintain prairie areas. They are working with landowners to restore and connect grasslands in several parts of Lambton County as well as in other southern counties. While much of the work at the present time involves small patches of prairie wherever they can fit it in, they are concentrating on three areas in Lambton County, and supplying plants to several others, all with good bobwhite potential, or with existing birds that can benefit from additional habitat. About three quarters of the work being done by the Stewardship Council revolves around habitat restoration that will be of direct benefit to bobwhite, other grassland birds, butterflies and the native prairie plants themselves (R. Ludolph, Pers. Comm.).
While the prairie restoration programs have only recently begun (1993), they have expanded considerably in the past couple of years, and are expected to continue to grow in future. Plans are to have habitat suitable for bobwhite available in sufficient quantity to be able to maintain transferred birds from other areas whenever birds become available, if local birds do not quickly benefit.
Surveys conducted in the summer of 1999 also indicated that in the area where bobwhite are doing well, they have excellent winter cover, enabling them to survive winter snow and ice conditions. Tall-grass prairie restoration also provides tall rank growth that makes good winter cover for bobwhite. However, there are a couple of factors that may make survival more difficult. Burning is apparently practiced to renew the prairies. That in itself is not a problem if only small areas are affected. But, especially in dry years more may be burned than is good, and if done in autumn and winter as it sometimes is, could decrease winter survival (A. Woodliffe, Pers. Comm.).
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