GREATER SNOW GEESE IN BREEDING, STAGING AND WINTERING AREAS

The single population of this sub-species breeds from northern Baffin Island and northwards and birds feed predominantly on sedges and grasses growing in moss-covered fens and in uplands during the summer. There is evidence of changes in habitat use by snow goose families, possibly in response to food depletion in the grass and sedge fens which are their preferred habitat. These are habitats where there is a well developed organic substratum, unlike the situation on the intertidal flats of the Hudson Bay coast. Parallels can be made between the two subspecies and their effects on vegetation, but there are also differences, primarily related to the use of different species as a prime source of forage.

Damage to Coastal Habitats in the Wintering and Staging Areas

Prior to the 1960s the geese fed almost exclusively in freshwater tidal marshes dominated by the bulrush, Scirpus americanus, particularly in the marshes of the St. Lawrence River (Giroux and Bédard 1987, Reed 1989). Smith (1983) reported that greater snow geese altered the species composition of salt marshes on the wintering grounds in North Carolina. The birds grazed intensively on Spartina alterniflora and on Spartina patens and the above-ground biomass was severely reduced (Smith and Odum 1981, Fig. 2.20). However, the vegetation was not eliminated and full recovery of the latter species occurred in exclosures which were protected for two growing seasons after grazing ceased. Scirpus robustus invaded heavily grazed patches of Spartina alterniflora. Stands of Scirpus americanus were unaffected by grazing, the percentage cover in grazed and ungrazed areas was not significantly different. Eleocharis species were only present in grazed sites. Of course, the geese grazed only during the period when the marsh plants were dormant, hence the effects of grazing and rhizome grubbing were not likely to be as severe as when active growth was occurring. Nevertheless, grazing/grubbing led to a decrease in net below-ground production and a change in species composition.

Formerly, staging in the St. Lawrence estuary occurred almost exclusively in the Scirpus americanus marshes, and even today, with many more geese and an expanded range, those marshes are of critical importance. Vigorous grubbing by the geese removed an estimate 74% of the underground biomass of Scirpus in one year in a major marsh area, however, no long term trend in abundance of the plant occurred (Reed 1989). In another marsh, it was demonstrated that net above ground primary production of Scirpus was lower in areas exposed to heavy grubbing by geese than in areas protected from grubbing (Giroux and Bédard 1987) but the heavily grubbed areas were maintaining their production (albeit at a lower-than-potential level) over the long term (Reed and Giroux, unpublished data). Expansion of the staging area downstream led to geese feeding on salt-marsh vegetation, including Spartina alterniflora and Spartina patens. Although marshes continue to be used as roost sites (Gauthier et al. 1988), the low abundance of Scirpus americanus and the high extraction cost and low energy return associated with Spartina roots has led to the birds feeding in agricultural land (Bédard and Gauthier 1989). The rhizomes of bulrush (S. americanus) are still an important component of the diet, but there are indications that demand is outstripping the regrowth potential of stands of bulrush, and that soft mudflats are replacing former stands of bulrush. A similar situation exists in the Fraser Delta in British Columbia, where lesser snow geese eat a substantial proportion of the total rhizome of each plant of Scirpus (Burton 1977). In addition, the geese there are increasingly foraging for waste crops on agricultural land (potato fields, corn and wheat stubble fields).

Damage to Agricultural Crops

Most of the reported damage to agricultural land in the USA by greater snow geese is associated with small grain crops, particularly winter wheat. Damage can result from a variety of causes but it includes removal of seedlings, grazing of plants, and the loss of seed heads (Anonymous 1981, Hindman and Ferrigno 1990). In some areas, the persistent foraging by geese has led to reduced wheat yields. The birds also glean grain from old fields of corn (Zea mays) and soybean (Glycine max) (Reed 1991). A crop damage insurance program began in Québec in 1992. Costs of reported damage to hay crops by GSGO in Québec from 1992-1995 are shown in Table 2.1.

Most agricultural land adjacent to the marshes in the St. Lawrence River is managed for hay production based on a 4-6 year rotation system with oats/barley, Phleum pratense, Trifolium pratense and Medicago sativa. In spring, geese graze the new green growth which is mostly Phleum (timothy grass). Heavy grazing on this growth and that of other forage species can significantly reduce hay yields at first harvest (Bédard et al. 1986, Reed and Cloutier 1990) which occurs from mid- to late-June (Reed 1991). This is approximately 3 to 6 weeks after the northward migration of geese from the area. In the Montmagny area where the grazing is particularly intensive, a mean loss of 14% in hay yield was recorded in old and new hay fields in 1980. By 1985 goose usage had tripled and hay losses at harvest had doubled (Bédard and Lapointe 1991). Yield loss is not uniform across the entire area but is concentrated in a few individual fields, hence the loss is disproportionately high for a small group of farmers. Gauthier and Bédard (1991) have experimented with forage mixtures which are less palatable to the geese. Among legumes, Trifolium pratense ranked highest and Lotus corniculatus lowest in preference. Among grasses, Phalaris arundinacea (canary grass) was the preferred species followed by Dactylis glomerata, Bromus inermis and Phleum pratense. They conclude that the substitution of Trifolium with Lotus would reduce the attractiveness of hay fields to snow geese.

Table 2.1. Crop damage by greater snow geese in Québec (data courtesy of Michel Lepage, Ministère de l'Environnement et de la Faune du Québec).

Preferred Forage Species on the High Arctic Breeding Grounds

Much of the information discussed below is based on the results of G. Gauthier and his group working on Bylot Island, NWT, where there is a large breeding colony of greater snow geese numbering 27,500 breeding pairs in 1993 (Reed and Chagnon 1987; Reed et al. 1992, and A. Reed, unpublished data).

Grazing by geese has had a major impact on the above-ground biomass of forage graminoid species and the effect of the geese on the vegetation has increased in recent years (Gauthier et al. 1995). Although Dupontia fisheri is the dominant plant in moss covered fens in which family groups of greater snow geese feed, the impact of goose grazing was more severe on Eriophorum scheuchzeri/angustifolium than on Dupontia. Peak above-ground biomass in ungrazed areas averaged 33 g dwt/sq m. In all years of a three-year study, it was estimated that geese consumed from 65-113% of the cumulative net above- ground primary production (NAPP) of Eriophorum species and 30- 78% of the cumulative NAPP of Dupontia. Grazed plants were able to grow new foliage, but grazing did not enhance NAPP, unlike at La Pérouse Bay where swards of Puccinellia phryganodes show increased NAPP following defoliation (Cargill and Jefferies 1984).

It is likely that this pattern of grazing is common in the high Arctic. Again, there are indications that with the increasing number of birds the swards may not be able to regenerate and foraging areas will become moss carpets. On the Tundra of the Academy on Wrangel Island this has occurred in the vicinity of shallow, thermokarst lakes (R. Jefferies, per. obs.). However, in general, there does not appear to be the level of damage in the high arctic that characterizes the coastal areas of the subarctic Hudson Bay lowland.

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