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James A. Estes

Publications and source records attributed to James A. Estes.

47 records · Page 3Linked to original sources
USGS1990

Indices used to assess status of sea otter populations: A reply

The California sea otter ( Enhydra lutris ) population, after increasing for more than half a century, stabilized and probably declined from the mid-1970's to the mid-1980's. Estes et al. (1986) suggested that the stabilization and decline were not due to food limitation. Garshelis et al. (1990) challenged this suggestion, although in doing so they misrepresented arguments made by Estes et al. (1986), provided no evidence for alternative hypotheses, and offered no constructive recommendations for a better means of population assessment. While acknowledging some of the points made by Garshelis et al. (1990), I believe the collective evidence presented by Estes et al. (1986) provided a reasonable basis for rejecting the food-limitation hypothesis, and point out that recent increases in the California sea otter population following a legislated reduction in net entanglement mortality is strong evidence against the food-limitation hypothesis.

California↗
USGS1988

A double survey estimate for sighting probability of sea otters in California

We developed an estimator for the probability of sighting sea otters ( Enhydra lutris ) by shore- based counters, based on simultaneous double-surveys. We then estimated probability of sighting sea otters in California and evaluated the estimator's principal assumptions. The overall probability of sighting sea otters on 5 replicated double-surveys at each of 6 study areas was 0.945. Estimated probability of sighting did not vary (P > 0.05) among study areas or over time and was not correlated (P > 0.05) with distance of otters from observers. Probability of sighting was affected (P < 0.05) by sea otter activity and group size. Activity-specific probabilities of sighting were: resting = 0.990, foraging = 0.769, and other = 0.885. All animals missed by 1 observer team were in groups of ≤ 2 otters, whereas 52% of the animals sighted during the study were in groups ≥ 3. Observer teams may have varied slightly in sighting ability, but this variation did not substantially affect population estimates.

California↗
USGS1986

Activity-time budgets of sea otters in California

Daily time budgets and activity patterns of sea otters ( Enhydra lutris ) were determined by scan sampling at 4 study areas in central California. Diet was determined by direct observation of foraging animals. Average time invested in foraging ranged from 11 to 71% among viewing areas (1-2 km of coastline) and from 21 to 28% among study areas (8-10 km of coastline). Foraging time budgets were unrelated to season or the length of time that an area had been inhabited by otters. The diet of sea otters in California consisted almost entirely of marine invertebrates. These patterns were consistent with our review of other information on sea otter activity and diet in California. Diurnal foraging patterns were distinctly crepuscular at all sites and times sampled but one. Afternoon peaks in foraging activity were greater than morning peaks. Time budgets and diets were similar to those of sea otter populations in Alaska and the Soviet Union that were known to be below equilibrium density, thus suggesting that the presently curtailed growth of the California sea otter population is not due to food limitation.

California↗
USGS1971

The functional significance of movements and positions of the pinnae of the African Elephant, Loxodonta africana

Observations of wild African elephants ( Loxodonta africana ) in Uganda indicated that flapping and spreading the highly vascularized ears are probably important functions for heat dissipation. Ear flapping increased as ambient temperatures rose and decreased or ceased during cold or rainy weather. Rate of ear flapping was inversely related to wind velocity. Spreading the ears reduced ear flapping, particularly when an elephant faced downwind. Stimuli that elicited alertness, excitement, or hostility caused elephants to raise their heads and spread their ears widely and rigidly, and large elephants occasionally flapped their ears loudly and sharply. Flapping and spreading the ears for heat dissipation are generally not interpreted as danger signals by other elephants.

Journal of Mammalogy↗