Gap crossing by chipmunks: an experimental test of landscape connectivity

Eastern chipmunks (Tamias striatus) are forest specialists common to eastern North America. Numerous studies suggest that chipmunks require fencerow corridors between woodlots to maintain functional connectivity in agricultural landscapes. We tested this hypothesis by conducting a homing experiment to assess whether chipmunks would cross nonforested gaps of different sizes. Chipmunks in 11 landscapes were translocated a constant distance of 220–250 m across gaps ranging in size from 0 (continuous forest) to 240 m (mostly gap). Logistic regression analysis demonstrated that the probability of an adult chipmunk returning to its home range was not related to the size of the gap that had to be crossed (χ2 = 0.781, n = 60, P = 0.377, ρ2 = 0.011). Chipmunks crossed the entire range of gap sizes and there was no evidence of a threshold in connectivity. These results suggest that forest woodlots may be functionally connected for chipmunks even without fencerow corridors, and that landscape configuration in the study area may not have isolating effects on chipmunk populations. More empirical studies are required to identify whether functional connectivity thresholds are present in mammal populations as theoretical studies suggest.

Displacement distance and quality of orientation in a homing experiment with deer mice (Peromyscus maniculatus)

Eighty-two deer mice were released at distances between 175 and 950 m from their home sites. The frequency of returns to the home site was higher among mice displaced over shorter distances than it was among mice displaced over longer distances. However, there is no evidence that the quality of orientation of the mice near the place of release or their rate of settlement in the release site area was dependent on the displacement distance.

Movements of Cutthroat Trout after Different Periods of Retention Upstream and Downstream from their Homes

A homing experiment of cutthroat trout (Salmo clarki) was carried out in Gorge Creek, a small trout stream more or less typical of the streams of the eastern slopes of the Rocky Mountains in Alberta. A half-mile portion of the stream was screened off and, into the enclosure thus formed, 105 trout were transferred from above and 104 from below. Each of these was given a numbered tag and the home locality was recorded. The transfers were made from June 24 to August 13. On August 15 the screens were removed; from September 3 to 5 most of the experimental area was poisoned with Fish Tox and the localities of tagged fish recorded. It was found that most of the trout that had been confined for 30 or more days remained in the enclosure area, i.e., they had adjusted to new homes. The exceptions appear to be the result of random movements. Trout of upstream origin, confined for less than 30 days, move toward their original home territory. Trout of downstream origin, confined for less than 30 days, show very much less ability to move toward or to find their homes. The hypothesis is put forward that trout are guided by smell in finding home.A few observations on size of home territory suggest that it is small, perhaps not more than 20 yards of stream. Trout may inhabit the same area of stream for at least three years.