Northern bobwhite (Colinus virginianus) COSEWIC status report: chapter 7

Population Sizes and Trends

What was probably a fairly small wild population in southwestern Ontario, prior to European settlement, underwent a considerable expansion following forest clearing in the early 1800s. The expanding population reached as far north as southern Georgian Bay and Kingston, although in any abundance, they were more limited to an area south of a line running from Goderich to Oshawa (Clarke 1954 – Fig. 2). Since reaching a population peak about the mid-1800s, the numbers of birds and their range has contracted slowly but steadily.

With declining populations, numerous releases of pen-reared birds were tried through much of the 20th century. But mortality rates of pen-reared birds have been found to be very high, and more recently such birds have been considered unsuitable for restocking (DeVoss and Speake 1995, Roseberry et al. 1987).

In the early 1970s there were estimated to be about 1055 coveys of quail in Ontario, each containing several birds, primarily in Lambton, Middlesex, and Elgin Counties (Holdsworth 1973). However, during three successive winters in the late 1970s, when weather, including icing, was severe, the population of bobwhite decreased further. In the early 1980s, the breeding bird atlas and the subsequent rare breeding bird program 1989-1991, revealed a scattered distribution, with reports from only 79 squares (Fig. 3). Many of the reported birds were also likely from releases, and not native wild birds. Overall, the abundance estimated during the atlas period was between 232 and 1545 pairs (Page and Austen 1994).

The atlas estimate came from a compilation of five years of data, and so may have been on the high side. The 1970s survey was also above the atlas upper limit, suggesting that, not only had the population not recovered from severe winters, but also that there had been a further decline (Page and Austen 1994).

Then in 1989-1990, an extensive mail survey in the southwestern ministry region suggested the population had fallen to only about 185 quail in 16 coveys (Hunter 1990). Further, it was considered that wild stock was probably persistent only in two disjunct areas in Aylmer and Chatham regions (Page and Austen 1994). The breeding bird survey from 1966 to 1998, while based on only three routes, recorded a highly significant decline in Ontario during the period. From 1980 to 1998, there were too few reports on only 2 routes to indicate significant change, although the trend was still downward (www.mbr-prec.usgs.gov/bbs/trend/trend 98.html).

Through the 1990s no complete surveys were conducted to assess population change. However, it was generally felt that numbers had probably risen slightly to 200 to 250 birds, and the population appeared to have stabilized at that level through most of the decade (P. Hunter, pers. comm., 1999).

Data from the three Breeding Bird Survey routes in Ontario that reported Northern Bobwhite (from the U.S. Breeding Bird Survey website (http://www.mbr-pwrc.usgs.gov/bbs/bbs.html) show a mean annual decline of 18.9 percent (p=0.04) for Ontario between 1966 and 2001. This represents a total decline of 99.9% over 35 years, or 88% per decade.

In the United States, in recent years, the species has also experienced significant declines in most states. From 1965 to 1995, regional, state wide, and local declines of 70 to 90 percent were common in 80% of states where it occurred (Brennan 1999). Declines were greatest in the southeast, and less in the midwest, with numerous extinctions of local populations. There were significant declines from 1966 to 1998 in Michigan, Ohio, Pennsylvania, and New York according to the breeding bird survey results. Those trends were also evident in the 1980 to 1998 period, but not significant in three of the four states (http://www.mbr-pwrc.usgs.gov/).  In the U.S., most losses have been attributable primarily to habitat loss from changing land use in agriculture, forestry, and urbanization (Brennan 1999).

In 1994, when first considered by COSEWIC, plans were underway to undertake a trap and release program using wild caught birds from a similar climatic type in the U.S. The Ontario Ministry of Natural Resources and the Ontario Federation of Anglers and Hunters were prepared to undertake this release program in both Middlesex and Elgin counties. The release would have been at least 300 birds, in an attempt to link scattered populations as well as to increase overall numbers. This would have been followed by the release of an additional 200 to 300 birds the following year (Page and Austen 1994).

However, with the concomitant severe declines reported in most U.S. states, they have been reluctant to further reduce their own stock for such a release in Canada. But, contact is being maintained with states from which potential transfers could be made, as soon as feasible. Bobwhite have a high reproductive potential. If U.S. populations rebound, there is a high probability of releases being made in Ontario in the near future. This initiative has not been abandoned, and the intention is to undertake it as soon as it can be arranged (P. Hunter, Pers. Comm., 1999).

More serious concern for the species status exists from some other observers. Bobwhite are reported to have disappeared from a number of areas in the past decade where they were traditionally known (D. Sutherland, Pers. Comm. 1999), indicating a continuing decline in some areas.

Overall the present population of Northern Bobwhite in southwestern Ontario, whether previously inadequately surveyed, or more fully recovered than expected, appears likely to be above the estimate of 185 birds given in the previous status report (Page and Austen 1994).

In May-June 1999 and May-July 2000, the Rural Lambton Stewardship Network and members of the Walpole Island First Nation conducted Northern Bobwhite whistling surveys on Walpole Island First Nation (called west Lambton County in James 1999), which is thought to contain the majority of the remnant habitat used by native birds in Canada.  MacIntyre (2002) and Hector (in prep.) have summarized the results of the surveys.

Sixty-five roadside stations were set up in grassland habitat on Walpole Island at least 1 km apart.  Whistling surveys were conducted ½ hour before sunrise to 1½ hours after sunrise during late May to July 2000. At each station, surveyors noted the number of male Northern Bobwhite calling during a 3-minute period.  It is estimated that 75% of the suitable habitat on the Island was sampled during the surveys.  Not all stations could be sampled on one day.  When stations were sampled more than once, the maximum number counted at a station was used in the estimate.

The total number of calling males recorded on the survey ranged from 92 during a 5-day sampling period in late June to 155 over a 23-day sampling period in June.  During the longer survey period there is a greater chance that males may have moved among survey stations which could inflate the estimate from double counting.  For the purposes of determining status, the lower estimate (92 birds) is more appropriate.

If one assumes that each calling male represents a pair and that densities in the unsampled habitat are similar to densities in the areas sampled (both untested assumptions), then this would result in an estimated breeding population of 230 birds on Walpole Island in 2000.  Further extrapolations can be made from this estimate to speculate on the brood production, the over-wintering population and severe winter survival (MacIntyre 2002, Hector, in prep.).

The total area of Walpole Island is 24,000 ha consisting of wetland, agricultural areas, prairie, savanna, hardwood communities and scattered residential development.  An analysis of core Northern Bobwhite habitat was carried out on Walpole Island in 2000 using LANDSAT imagery, ArcInfo analysis and ground-truthing.  A total area of 1840 ha (7.7%) was identified as prime grassland and savanna habitat.  Many peripheral habitats, including forest openings, backyards, fencerows, dykes and even agricultural areas can be used by Northern Bobwhite as well.

It is generally believed that the Northern Bobwhite at Walpole Island are of native origin. There is less certainty about the numbers and origin of birds found away from Walpole Island. Although not a comprehensive survey, preliminary data from the Ontario Breeding Bird Atlas (3 of 5 years completed) show Northern Bobwhite from 17 locations away from Walpole Island (Figure 4).  Ontario Ministry of Natural Resources staff report that additional unmapped locations are known but have not been consistently recorded or tracked.  While some of these locations are on lands adjacent to Walpole Island, others are across a broader area of southwestern Ontario.

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