Part II

HIGH GOOSE POPULATIONS:

CAUSES, IMPACTS AND IMPLICATIONS

KENNETH F. ABRAHAM, Ontario Ministry of Natural Resources, Box 5000, 10401 Dufferin Street, Maple, ON L6A 1S9

ROBERT L. JEFFERIES, Department of Botany, University of Toronto, 25 Willcocks Street, Toronto, ON M5S 3B2

INTRODUCTION

Many species of Arctic breeding geese have increased significantly over the last thirty years (Ogilvie and St. Joseph 1976, CWS, USFWS and Atlantic Flyway Council 1981, Boyd and Pirot 1989, Owen and Black 1991, Fox et al. 1992, Abrahamet al. 1996). In North America, these include lesser snow geese (Anser caerulescens caerulescens), greater snow geese (A. c. atlantica), Ross' Geese (A. rossii), greater white-fronted geese (A. albifrons), and some populations of Canada geese (Branta canadensis), e.g., B.c. interior of the Mississippi Valley Population and B.c. parvipes of the Short Grass Prairie Population. In addition, some temperate breeding Canada geese (B.c. maxima) have also increased (Rusch et al. 1995, Allan et al. 1995). Most increases are the direct or indirect result of human activities; their combined effects represent biomanipulation of goose populations on a massive scale. The mid-continent population of lesser snow geese, for example, now exceeds three million birds, and the population is increasing at a rate of at least 5% per annum (Abraham et al. 1996) (Fig. 2.1).

The intense foraging activities of lesser snow geese, greater snow geese, Ross' geese and some Canada goose populations, have altered plant communities in both natural and agricultural ecosystems (Lynch et al.1947, Smith and Odum 1981, Giroux and Bédard 1987, Jefferies 1988a,b, Kerbes et al. 1990, Belanger and Bédard 1994, Didiuk et al. 1994, Ryder and Alisauskas 1995). Most species of geese feed in flocks on migration and wintering grounds. Many, including lesser snow geese, also feed in groups on the breeding grounds following hatch, hence it is not only the large numbers of birds, but also their colonial or gregarious behaviour and locally high densities that cause substantial changes to plant assemblages.

The chronic effects of disturbance by geese to different types of vegetation and soils are cumulative. Females display a high degree of philopatry to breeding grounds (Cooke et al. 1995) and in response to overall population growth, individual nesting colonies expand outward to occupy all suitable habitat and/or increase in density within suitable habitats (e.g. Ross' geese, Alisauskas and Boyd 1994, Kerbes 1994). The sustained use of a breeding site over a number of years allows little opportunity for recovery of the vegetation from the effects of foraging. The intensity of foraging, particularly in spring, varies from year-to-year and is dependent on the number of birds and on the prevailing weather conditions. In late springs, the prolonged cold and the presence of ice and snow delays the northward migration of birds, and at sites in the sub-Arctic and southern Arctic both local breeding populations and staging birds have considerable impact on vegetation (Jefferies et al. 1995). Most damage to vegetation, so far recorded, has occurred in habitats along the western and southern coasts of Hudson Bay and in James Bay. These localities, which are major staging and breeding areas for both lesser snow geese and

Canada geese, are undergoing isostatic uplift (ca. 1 cm/yr) and plant community development in these early successional environments is strongly dependent on coastal geomorphology. The destruction of vegetation which occurs at sites frequented by geese is the direct result of foraging and feedback processes that lead to further destruction of vegetation and desertification of landscapes (Srivastava and Jefferies 1996). The rate of loss of vegetation is rarely linear, once a threshold associated with the intensity of the feedback processes is passed, destruction is rapid (see later).

The effects of this cumulative damage on the geese and other fauna, on wetland and agricultural ecosystems, and on migratory bird management are significant and complex. Arctic coastal wetlands and their biological processes and components, in particular, are at risk from sustained high goose populations. The biology and well-being of individual geese have been affected (e.g., reduced body size, reduced gosling survival). Ducks, shorebirds and passerines suffer direct habitat loss, particularly nesting birds that are less mobile. Degraded soils alter the conditions for invertebrate and microfaunal growth. Aquatic systems in coastal areas are affected by eutrophication, increased water temperature, salinity, and increased evaporation, with probable consequences on the structure of invertebrate communities. In areas long-occupied by geese, faecal droppings have accumulated, and conditions may favour the spread of parasites and diseases, (e.g., renal coccidiosis, Gomis et al. 1996).

There are few precedents for dealing with problem (high) populations of migratory game birds. For harvestable wildlife in general, the wildlife conservation profession has focussed on ensuring stable or increasing populations consistent with wise use. For non-harvested wildlife it has emphasized protection or halting declines of rare species; it has dealt relatively little with population reduction or control of abundant native vertebrates (Garrott et al. 1993) except where rare or endangered species recovery is limited (Goodrich and Buskirk 1995). The dilemma posed by high populations of geese present new challenges (Ankney 1996, Rusch et al. 1996) made more difficult because many of the negative impacts occur far away and unseen by the general public, whose understanding and support will be needed for action.

In this background report, we review status and trends of selected goose populations, the contributory causative factors, the biological impacts of high populations, the likelihood of recovery of affected systems, and some of the human interactions. In companion reports, the effects of various population manipulations is considered (Rockwell et al. 1997) and possible management actions are reviewed (Johnson 1997).

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