The policy requiring local government decision making and
funding, we believe, is the key to the success of the Metro Twin Cities goose
management program. It has thwarted attempts to stop or delay any of the 737
captures done in the past 15 years. Phone or personal public contacts with agency
personnel and recent legal actions have been sufficient to test the policy. When
someone was opposed to a management practice, the individual was directed to the
appropriate city official. Demands to manage sites not approved by a city have been
processed in a similar manner. To date, no city has terminated a removal program
because of citizen opposition. In 1993, a suit by the People for Ethical Treatment
of Animals (PETA) ended in a court review of the program and an environmental
assessment (MNDNR 1994). Neither program administration nor operational procedures
were altered as result of this suit.
Short-term, goose redistribution techniques have limited
success. Of 12 techniques evaluated 2 worked consistently. Fencing kept adults and
broods off sites in summer and harassment by dogs in both summer and fall. The
latter appears to highly successful for fall concentration on golf courses and
athletic fields.
Egg removal eliminated 97% of the production on 3 large
wetlands, but the procedure was expensive. An average of 1.7 eggs/hour were found.
At a nest search cost of $10.85/hr ($8/hr wage plus travel and equipment), it costs
$6.38/egg destroyed. Compared with an average cost of $10/goose for capture and
relocation and $24/goose for trap and process, egg destruction appears more cost
effective. However, removing an egg does not reduce a population as quickly as
removing an immature or breeding adult. We developed a composite life table to make
the comparisons. Starting with 1000 eggs, a nest success of 75%, an egg success
(eggs hatching/successful nest) of 97% (Sayler 1978), 75% gosling survival to capture
time (6 weeks of age) (Sayler 1978), an 75% immature and 85% adult annual survival
rates (Cooper unpubl. data), we computed the number of eggs each immature and adult
trapped represented. Each egg destroyed represented 0.55 immatures at capture,
equivalent to a cost of $11.60/immature. Because urban geese have high survival, the
average age of a breeding adult is 9 years, thus each egg destroyed represents 0.08
breeder, equivalent to a cost of $80/adult reduced. Over the years, we have captured
1.8 immatures/adult (Table 1), therefore using this age ratio, we estimated an
overall cost of $36/goose reduced by egg destruction.
We believe that by requiring the cities and towns to pay
for the capture and transport, the scale of the removal has been damped by
economics. While complaints have increased rapidly since 1982 (Figure 5), the
number of trap sites has grown more slowly and appears to have stabilized (Figure 4).
For example, these data suggest that in the absence of a charge, we would have had to
removed nearly 4 times (397:101) as many geese in 1996.
The relocation results document that the procedure can
reduce populations of Canada geese in metropolitan communities. However, the
efficacy varied widely and typical it took 5 or more years to attain a 50% reduction
in bird numbers. The effectiveness apparently was influenced by the available nest
sites, the degree of isolation from other goose concentrations, and the return of
relocated adults. Isolated sites with limited nesting habitat showed a progressive
population decline. Sites with excellent nest sites (islands) continued to attract
breeders even when surrounded by urban development, whereas, rural sites with an
abundance of nesting habitat and adjacent breeding populations showed a slower
decline. The return rate of relocated adults suggests the expected population
reduction would be more than twice that observed if none returned to breed. This
was clearly demonstrated by the fact that relocated adult females constituted 50% of
the breeding females captured in some years. Therefore, the processing of adults
should improve the removal effectiveness by a equal proportion.
Sport hunting was the least costly population management
method for cities (Table 5), however, 77% of Metro is closed to the discharge of
shotguns. Hunting does appear to have had a major effect on populations. The hunted
zone goose density was 3 times lower than in the unhunted portion of the Metro.
While the density difference might reflect differences in the expansion of the
breeding geese from the establishment location (Cooper 1978), it is unlikely. Only
3 of 13 goose establishment sites found by Cooper and Sayler (1974) were in the
unhunted zone . As human densities increase, hunting will undoubtedly decline, but
at present it is an important component of the management program.
Table 5. Estimated costs of Canada goose population management methods, Twin Cities, Minnesota.
_______________________________________________ Procedure Cost ($/Bird Reduction) _______________________________________________ Sport Hunting 0 Relocation 10 Process for Food 24 Destroy Eggs 45 Sterilization 100a Habitat Modification Very High _______________________________________________ aEstimated from University of Minnesota College of Veterinary Medicine.
Habitat Reduction
Habitat modification to redistribute geese, while limited as present, may have some potential for alleviating goose damage. But as a population control tool we doubt that enough shoreline could be converted to non-mowed grass to limit the goose population at an acceptable level. To do so would impact most wetland and lake shore residential lawns, beaches, many parks, athletic fields, golf courses, and so forth. It is unlikely that such a change would be acceptable the public. Moreover, if there were major reductions of mowed grass, the geese would simply concentrated on the remaining habitat where mowed grass if integral to the human use, e.g., golf courses, athletic fields, etc.