Canada goose habitat use differs during breeding, brood-rearing, late summer and fall staging, and over-wintering (Owen 1980), consequently, the potential for moderating or eliminating goose damage by changing the habitat differs by season.
Nest habitat
Canada geese nest in a wide variety of situations. The most common sites are islands, muskrat or beaver lodges, and peninsulas, (Hanson 1965, Williams 1967, Sherwood 1968, Hanson and Eberhardt 1971, Cooper 1978, Ogilvie 1978, Owen 1980, and others). Where preferred sites are limited or absent, birds utilize cliffs (Kondla 1973), abandoned eagle and heron nests (Craighead and Craighead 1949), and the flat roofs of buildings (Cooper Unpubl.). When alternatives sites are lacking, Canada geese nest in colonies on islands (Klopman 1958, Ewaschuk and Boag 1972). Canada geese also readily nest in man-made structures when provided (Dill and Lee 1970, Cooper 1978).
Potential alterations of Twin Cities nest habitat for either short-term or long-term goose management are extremely limited. Drainage or filling of urban lakes and wetlands would control the geese, but would be costly, and have unacceptable impacts on other wetland wildlife species and diminish the landscape quality for humans (Ulrich 1983). Currently all of Metro wetlands used by nesting geese are protected by Minnesota law. Nine percent of the Twin Cites 3,103 lakes and wetlands contain an average of two earthen islands. Because islands are favored by nesting geese and nest success is high on islands (Sherwood 1968, Ewaschuk and Boag 1972), removal of these sites would reduce local goose populations, e. g., at Lake of the Isles in Minneapolis where up to 60 pairs have nested. But islands are preferred breeding sites by other wildlife species, particularly ducks, herons, and egrets, thus island removal for goose management would significantly impact other species. The removal of man-made structures should be done at complaints sites, however, this would have minuscule effect on the Metro population. In the early 1970s, man-made sites were commonly provided at goose flock establishment locations; Sayler (1977) found 100 nests (30% of the total) in structures in 1973-75, whereas, no structures currently exist at the 10 sites studied in the 1973-75 period, and no structures were found at the 254 randomly surveyed wetlands in 1994.
Brood-rearing habitat
Because 94% of the Twin Cites goose damage complaints occurred during the brood-rearing period extending from mid-May to mid-August, modifications during this interval would appear to have great promise. The high level on human/goose conflicts during brood-rearing is undoubtedly related to the restricted range (the adults are flightless for 5 weeks and the goslings 10 weeks), the bird's high forage demand, and the significantly higher human use of the landscape in summer, particularly shorelines for hiking, fishing, swimming, picnicking, etc.
Metro Canada goose broods hatch from April 30 to June 15 with a peak in mid-May (Sayler 1977). Pairs typically move their young to suitable nearby shoreline free of obstructing vegetation where they graze on forbs and grasses, particularly bluegrass (Poa spp.). If suitable shoreline is unavailable near the nest--in many cases even when it is--the goose families move to traditional brood-rearing sites within a week or two (Zicus 1981, Schultz et al. 1988). While most movements are less than 1-2 km and often along water courses and other greenway corridors, neckbanded Twin City pairs have traveled from 6-15 km from nest to brood-rearing site through city streets; in 7 cases over fenced interstate highways where only arterial overpasses permitted passage.
Because the geese are traditional in their use of brood-rearing sites (Zicus 1981, Schultz et al. 1988), the wetlands used during this period are predictable, and likewise, so are the goose damage complaint locations. While many (62%) of the brood-rearing areas are along the shores of the large lakes, where parks beaches, and suburban residential homes are concentrated, birds are also found on relatively small (<0.5 ha) golf course, apartment, townhouse, and residential ponds.
Alternatives to Managing Existing Turf
The apparent short-term solution in these cases is to discourage the geese by reducing the forage quality or availability, or by modifying the shoreline so that geese cannot move from the escape cover to the upland grazing area. Gosser et al. (1997) suggested that reduced lawn mowing or fertilization will discourage the geese. The recommendation appears sound; when present, Metro geese concentrate on newly-laid, fertilized sod and consistently frequent lush mowed sections of wetland shoreline for grazing. However, there are cases of Metro geese rearing their young on unmowed, cool-season and tall prairie grasses when confined by fences. Until controlled by removal (Cooper 1991), Wood Lake Nature Center fledged 60-120 goslings on an area containing 11 ha of unmowed and unfertilized tall grass prairie. Similarly, the fenced 85 ha Mother Lake near the International Airport produced from 25 to 75 goslings without any management of the grass. Thus, the response to either not fertilizing or mowing is dependant upon the availability of an alternative site with suitable grass. In short, the birds will go elsewhere if an alternative is available, but will continue to use unfertilized and unmown grass if there is no other option.
Turf Replacement
Removing and replanting the upland grass with rough grasses (tall grass prairie, tall fescue, etc.), ivy, shrubs, or trees should force the birds to use alternative turf areas. However, there is a paucity of research in this area, and as the Wood Lake example illustrates, the degree to which rough grasses discourage geese is problematic if alternatives are absent. Alternative plant cover selection constraints include climatic suitability, tolerance to flooding (Metro wetland water levels vary as much as 3 m), palatability to geese, life form (i.e. dense enough to preclude goose movement to abutting grazing areas), and effect on the landscape quality to humans.
From a long-term management prespective, if sufficient shoreline was converted from grass to vegetation not used by geese, the population would become limited by available brood-rearing habitat. To assess the magnitude of habitat conversion necessary to limit the Twin Cities goose population at its present level (25,000 birds in summer), the amount of Metro shoreline in mowed grass (see Cooper and Keefe 1997), and the goose carrying capacity of a hectare of grass were estimated. Using areas of the 3,103 Metro wetlands and a shoreline development value of 1.5, Twin Cities has a minimum of 5,325 km of shoreline. Based on estimates of grass shoreline made at 227 wetlands in 1994, Cooper and Keefe (1997) found that one quarter (25.1%) of the Metro shoreline was in mowed grass or pasture. Thus 1,331 km of shoreline is currently in mowed grass or pasture. Because Metro geese have been observed leading broods through 70 m of dense cattail and woods and more than 200 m of grass to graze, it was assumed that broods would utilize at least a 100-m grass strip along the shoreline for grazing, thus the Metro contains 13,310 ha of preferred brood-rearing habitat. The literature lacks Canada goose brood carrying capacity data, consequently carrying capacity was estimated from the goose pasturing done in 1996 as part of a Metro food-shelf program (Keefe 1996). Six hundred and fifty birds (500 Adult geese and 150 immatures) maintained normal weight growth on a 23 ha bluegrass pasture from August 1 to November 15, 1995. Thus a hectare of unmanicured pasture grass may support a minimum of 28 geese. If this is representative of the capacity of fertilized and mowed urban lawns to support geese, then the Twin Cities brood carrying capacity is 373,000 birds, and 93% of the existing lawns and pastures would have to be converted to limit the population to 25,000 geese.
Vegetative Barriers
Gosser et al. (1997) and Garner Lee Limited (1997) report that vegetative barriers such as trees and shrubs discourage goose transit. Grandy and Hadidian (1997) state that by "allowing grass and shrubs to grow as little as eighteen inches high in a ten foot band around a pond can act as a deterrent to geese as it will impede their access to grazing and block their view of predators." My observations of goose behavior in the Metro area over the past 20 years suggest that, while locations with good visibility (see Buchsbaum and Valiela 1987, Conover and Kania 1991) are selected for grazing, the species is capable of adapting to situations where dense shoreline vegetation exists and use it as escape cover. For example, Metro geese using a corporate grounds with 3 wooded- and 2 mowed-grass-shoreline wetlands separated by up to 300 m by woodlands with dense shrub understories. These birds have consistently been found on all of the wetlands during brood-rearing and observed to travel through the woods to access them. In another case, geese using a 1 ha pond surrounded by robust tall grass prairie >1 m in height, moved 120 m to graze on a 20-m bluegrass strip surrounding a commercial building. This behavior has been observed for other Canada geese. Lebeda and Ratti (1983) working with Vancouver Canada geese (B. c. fulva) and Byrd and Woolington (1983) studying Aleutian Canada geese (B. c. leucoparia) reported extensive use of dense vegetation for nesting, foraging, and escape cover during brood-rearing. In fact, Lebeda and Ratti (1983) report that dense forest was preferred to water as escape cover. Both studies were of island populations with either no (Byrd and Woolington 1983) or low densities (Lebeda and Ratti 1983) of mammalian goose predators typical of non-urban midwestern habitats, i.e. red fox (Vulpes fulva) and coyote (Canis latrans). Twin Cities urban goose habitat, particularly the highly developed zones containing most of the goose damage sites, support low densities of mammalian goose predators, and thus may present an ecological setting similar to that of islands. Therefore, goose brood-rearing behavior appears adaptive and dense vegetation, when predators are uncommon or absent, may be used. This hypothesis would explain my observations that geese during the brood-rearing period readily move through dense vegetation when visually open pathways are unavailable. More research is needed on the goose barrier attributes of vegetation prior to investing in expensive (see below) changes.
Man-made Barriers
Man-made barriers, blocking passage from wetlands to upland grazing locations, particularly during the flightless brood-rearing period in June and July, appears to be one of the most effective methods of limiting goose damage at specific locations. Barriers include electrified and non-electrified temporary (rope, wire, or bird-scare tape) and permanent wire or wooden fences, boulders, wooden boardwalks, construction vertical banks, and floating "bird" balls (Cooper and Keefe 1997, Garner Lee Limited 1997, Gosser et al. 1997, Smith and Craven, In Press). Drawbacks to the enclosure approach included entrapment of goslings, potential impacts on other wildlife, interference with human activities, and landscape quality.
Cooper and Keefe (1997) found permanent and temporary fences to be an effective short-term technique. Because of the poor visual aesthetics of fences, Gosser et al. (1997) recommended, that fences be placed in the water and screened with emergent vegetation; they also stated the "pond edges should be completely fenced." If the wetland contains breeding habitat and is surrounded by a permanent fence placed in this manner, available forage may be insufficient for goslings hatched within the enclosure, and they may starve. Two cases of entrapment were recorded in the Twin Cities in 1997. In one case, 7 pairs of geese with 25 goslings were entrapped by homeowner-constructed fences. After 10 of the 6-week old young were reported dead by a resident, the emaciated survivors were trapped and removed. In another case, 38 geese were entrapped in a newly constructed fountain basin with fences and vertical banks >1 m. When discovered, 3 of the 38, 4-week old goslings were dead and the remainder emaciated. In order to assure humane use of barriers, sufficient grazing must be provided within the enclosure to accommodate the expected hatch.
Piling-supported or floating boardwalks are used at 17 Metro goose complaint sites. These structures appear to restrict goose brood travel during the first 5 weeks of brood-rearing when the goslings are too small to surmount them. But, based on the complaints received, once the broods can access them, boardwalks become preferred loafing sites and residents spend considerable time washing goose manure from the walks.
Like fences, abrupt shorelines (>0.5 m with >60o slope) thwart goose movement. Because of the flat Twin Cites topography, they are uncommon in the Twin Cites except on the east and southeast shorelines of the larger lakes where wind-driven waves cause flooding and erosion. Here wood, concrete, or rock rip rap is used to secure the soil. Because of the construction expense, I suspect that these structures will not be used specifically as a goose deterrent. In addition, abrupt shorelines constitute a serious human drowning risk, particular to small children (U.S. Army Corps 1991).
Fall And Winter
Once flying in late summer, the geese cease using many of the small wetlands and concentrate on the larger marshes and lakes. From these staging locations, they frequently feed on the shorelines or fly to large open expanses of grass to forage. This explains the significantly lower number of complaints in fall compared to summer (94% vs. 5%), and the shift from residential sites, the most common brood-rearing period complaint type, to golf courses, athletic fields, and airports. Winter reports are even lower (<1%), undoubtedly because most (>95%) of the birds migrate in late fall and the wetlands are frozen and snow-covered.
The bird's mobility combined with a preference for feeding sites where the existing landscape is essential for the intended human use, severely limits the potential for habitat modification. Gosser et al. (1997) recommended planting tall-growing trees to obstruct the birds' flight paths into problem sites. Indeed, the presence of trees surrounding many of the small wetlands used during the flightless period may be the reason that geese discontinue using these wetlands once they can fly. Trees conflict with human activities at airports, athletic fields, and golf courses. Moreover, expanses of grass such as fairways and open water often serve as landing and take-off zones from which the birds walk or swim to the feed areas. Alternatives to goose-palatable grasses at airports have been investigated (Austin-Smith and Lewis 1970, Smith 1976), but no plant species have been identified that meet airport runway constraints: low height, low maintenance, relatively non-flammable, not attractive to other wildlife, etc. Overhead wire grids preventing geese from landing on a pond have successfully reduced use, but also precluded recreation such as fishing, swimming, boating, etc. (Lowney 1995) and impact non-target large birds such as herons, egrets, etc. Garner Lee Limited (1997) suggested that covering pond surfaces with floating "bird" balls could be highly effective, but also pointed to significant impacts on other wildlife.