TIME AND ENERGY BUDGETS OF THE MOCKINGBIRD (MIMUS POLYGLOTTOS) DURING THE BREEDING SEASON

A time and energy budget of male and female Mockingbirds (Mimus polyglottos) in six phases of their breeding cycle was completed using the equivalent temperature model to predict perching metabolic rates. Recorded time-budget behaviors included perching, bipedal locomotion, flight, and the time spent in the sun and shade. Over the total study period, males and females spent an average of 92.3% and 92.8% of their active day perched, 2.4% and 1.6% in bipedal locomotion, and 5.3% and 5.6% in flight, respectively. BMR plus thermostatic requirements averaged, seasonally, 78.1% of DEE tot in males and 76.1% in females. The choice of shaded or exposed microhabitats made very little difference in energy expenditure. DEE tot varied from 96.9 kJ in males with incubating females to 113.0 kJ in males caring for fledglings, and from 75.1 kJ in incubating females to 113.2 kJ in females caring for fledglings. Unmated, pre-nest-building, and incubating birds spent significantly less energy than did birds caring for nestlings (P < 0.05) or birds caring for fledglings (P < 0.05). With the exception of the nest-building phase, when females are producing eggs, and the incubation phase, when females gain insulation from the nest, male and female DEE tot closely paralleled each other throughout the season. The large amount of predation that occurred at the study site suggests that birds may allocate time to perching to minimize the probability of predation on themselves or their offspring.

DOUGLAS W. BIEDENWEG, The Auk 100: 149-160. January 1983