The impact of roads, pipe lines, and other human disturbances on caribou (Rangifer tarandus) migration is controversial but largely unknown. New research shows that the construction of a hydroelectric dam in Newfoundland, Canada, disrupted caribou migration and land use.
“The development caused a disruption of migrational timing during construction and longer-term diminished use of the range surrounding the project site,” say Shane Mahoney of the Newfoundland and Labrador Wildlife Science Division in St. John’s and James Schaefer of Trent University in Peterborough, Ontario, in the October issue of Biological Conservation.
Most studies of how disturbance affects caribou have failed to show decreased survival or reproduction. However, the researchers stress that the “absence of evidence does not constitute evidence of absence.” Caribou are difficult to study in part because they have such big ranges, and most studies have relied on population-level changes in distribution or short-term changes in behavior.
To study how development affects individual caribou and longer-term behavior, Mahoney and Schaefer monitored 54 adults that were radio-collared before the construction of a hydroelectric dam at Star Lake, Newfoundland. Star Lake lies along the primary migration route of the Buchans Plateau Caribou Herd, which has about 7,500 caribou. The 5-year study started two years before the dam’s construction began in 1997.
The researchers found that construction disrupted the timing of migration at the individual level. Before construction, individual caribou arrived at and departed from the calving/summer grounds in an order that was generally consistent from year to year. However, during construction this pattern was disrupted. Although the pattern was reestablished after construction, this finding shows that “there is a great deal we don’t know about how developments affect caribou,” says Mahoney.
The researchers point out that previous studies of the effects of development on caribou would not have revealed any differences at the individual level. “Herd animals are not clones, although our science often implies otherwise,” says Mahoney. “In social mammals, individual responses do eventually reflect population level changes.”
Mahoney and Schaefer also found that the caribou avoided the hydroelectric development site during construction. Before construction, more than half of the caribou studied were within three kilometers of the site during the summer, but after construction began, less than a quarter of them came that close. This finding supports results from previous studies, which have shown that caribou are less likely to use parts of their range within 1-5 kilometers of development. “The evidence is now sufficient, in our view to predict the effective loss of habitat at this scale, in a zone beyond the physical development,” say the researchers.
Mahoney and Schaefer call for more such long-term studies of how disturbances affect caribou at the individual level, cautioning that developments may have cumulative effects on caribou populations and that there may be a threshold level of the amount of development that caribou can withstand.
Mahoney, S.P. and J.A. Schaefer. 2002. Hydroelectric development and the disruption of migration in caribou. Biological Conservation 107:147-153.