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COSEWIC Assessment and Status Report on the Yellow Rail in Canada

Limiting Factors

Habitat Loss

A detailed analysis of habitat loss for Yellow Rails was presented above in “Trend in quality and quantity of critical habitat”. The salient points are summarized below.

Wetland loss unquestionably is the greatest threat to the Yellow Rail (Eddleman et al., 1988, Bookhout 1995), both in Canada and in the U.S., and there is no doubt that the population has been affected by habitat loss and degradation (Robert 1997). Loss of habitat known to have been used in the breeding season by Yellow Rails has been documented in Oregon, northwestern Ontario, southern Ontario, and southern Québec. We have not been able to find similar documentation in the prairies, but the landscape changes that have occurred there are very well documented. Hence, from a largely pristine environment at the turn of the century, the prairie-parkland region now comprises the largest expanse of agricultural land in Canada (Turner et al. 1987), and as of 1986, about 40% of the original wetlands in Prairie Canada had been lost (Canada/United States Steering Committee 1986). There is little doubt that considerable amounts of Yellow Rail habitat have been lost in this region. Specific documentation is lacking only because litte work has been done there on the species.

Habitat loss is occurring even in the last pristine stronghold, the west coast of Hudson/James Bay. However, it is unclear how much of a problem this currently poses to Yellow Rails, and there is uncertainty regarding the future dynamics of the enormous Snow Goose population.

Habitat loss is also a concern regarding the smaller U.S. breeding population. The status of habitat in the U.S. is also important because the entire global population migrates through that country. However, the most important limiting factor for Yellow Rails, regardless of where they breed, is habitat loss on the wintering grounds, which has been so extensive that the wintering range may no longer be contiguous (T. Bookout, pers. comm.). In Texas and elsewhere in the U.S. wintering grounds, the species seems to be largely restricted to a narrow band of coastline, and coastal marshes throughout the Gulf states are threatened. The size of the known wintering range is no more than 7% the size of the breeding range (277 800 km2 compared to 3 787 000 km2).


Other Limiting Factors

Harvest of wild and planted rice results in nest destruction and excessive disturbance to rails (Fannucchi et al., 1986, Eddleman et al., 1988, del Hoyo et al., 1996). Many Yellow Rails are apparently attracted to Louisiana rice fields (in fall and probably during winter also) and the potential for Yellow Rail casualities during harvesting is important. In fact, most specimens at the Louisiana State University Museum of Natural Science were found killed or mutilated by hay mowers near Baton Rouge (Cardiff and Smalley 1989). Evidence of this sort of injury has also been reported by Lowery (1974). A large portion of the Ile aux Grues (Québec) wet meadows is mowed annually from late-June to September, and farmers there have accidentlly killed some (Robert and Laporte 1996). Others have had their legs cut off during harvesting in the Abitibi region (Cyr and Larivée 1995).

Other less important limiting factors include lead contamination, hunting, disturbance by birders and collisions during migration. Lead shot is a major contaminant that can potentially affect rails (Eddleman et al., 1988). Some have been found in the gizzards of many Soras in the U.S. (Artmann and Martin 1975, Stendell et al., 1980); the highest incidences occured in marshes with tidal action, on waterfowl refuges, and on areas that have long been used for hunting. This threat has likely diminished with the decrease in the use of lead shot in favour of steel shot for waterfowl hunting. The effects of contaminants on rails are poorly known (Eddleman et al., 1988), and there is no indication one way or the other that Yellow Rails have been affected by the widespread use of pesticides in marshes (Ripley 1977).

Although it is illegal to hunt Yellow Rails anywhere in the U.S. and in Canada (except in Ontario and in the Yukon), a few individuals are likely taken, accidentally or otherwise, especially by waterfowl and Common Snipe (Gallinago gallinago) hunters (see Meredith 1935). No rails have been legally hunted in Canada since 1994 (Dilworth-Christie and Dickson 1997) and the sport probably has a minimal impact on populations. Yellow Rails may also be killed by flying into TV towers, telephone wires and lights (Barrows 1912, Roberts 1932), and some get stranded in large cities (Bull 1974, Whelan 1975). Thirteen individuals were once found at the foot of a 500 m TV tower in Texas (Pulich 1962). The impact of such accidents on populations is unknown (Bookhout 1995).

The Yellow Rail is greatly sought after by birders, and frequent visits to a site can cause considerable disturbance. For example, 70 participants in an annual American Birding Association meeting went to McGregor Marsh in Minnesota, surrounded, and captured a Yellow Rail (Bernstein 1988). Similar reports have emanated from elsewhere, especially Québec (Cyr and Larivée 1995). Fortunately, the famous “Rail Buggies”, used for flushing wintering rails in the Anahuac National Wildlife Refuge (Texas) and other U.S. wintering areas, were discontinued about 10 years ago because many rails were killed and the habitat was greatly affected (Holt 1993, K. Mizell pers. comm.).


Predators

Walkinshaw (1939) found two dead Yellow Rails that had been killed by a raptor and observed the remains of one in an owl pellet. A radio-tracked bird in Québec (Robert and Laporte 1996) was apparently taken by a Red Fox (Vulpes vulpes), while another was retrieved by a House Cat (Felis catus) in Indiana (Kirkpatrick 1980). Herons (Ardea herodias, Casmerodius albus) may eat a large number of rails during extremely high tides if adequate upland cover is unavailable around tidal marshes (Evens and Page 1986, Eddleman et al., 1994). Birders have reported having seen Yellow Rails hunted in this opportunistic fashion at Point Reyes (California), where the species is considered of exceptional occurence (P. Lehman and C. Elphick, pers. comm.). Northern Harriers (Circus cyaneus) and Short-eared Owls (Asio flammeus) frequent breeding sites in Michigan and Québec and are potential predators (Bookhout 1995, M. Robert, pers. obs.). In Texas, the Water Moccasin (Agkistrodon piscivorus) is a known predator, and other likely predators include Northern Harriers, Raccoons (Procyon lotor), Minks (Mustela vison), Bobcats (Lynx rufus), and possibly Barn Owls (Tyto alba) (K. Mizell, pers. comm.).