AVIS-IBIS

Birds of Indian Subcontinent

Breeding Energetics and Thermal Ecology of the Acorn Woodpecker in Central Coastal California

Publication Type:Journal Article
Year of Publication:1990
Authors:Weathers, WW, Koenig, WD, Stanback, MT
Journal:The Condor
Volume:92
Issue:2
Date Published:1990
ISBN Number:00105422
Keywords:Melanerpes, Melanerpes formicivorus, Picidae
Abstract:We used the doubly labeled water (DLW) technique to measure the field metabolic rate (FMR) of adult (n = 4) and nestling (n = 30) Acorn Woodpeckers (Melanerpes formicivorus). Resting metabolic rate (RMR) of adults and nestlings was calculated from O2 consumption. We constructed the nestlings' energy budget from measurements of the growth rate, FMR, and RMR of different aged nestlings. We measured the body temperature (Tb) of two nestlings in the field using implanted radiotelemeters, assessed the nestlings' thermal environment in terms of the air temperature (Ta) experienced inside and outside of nest cavities, and studied the ontogeny of nestling homeothermy in the laboratory. Adult FMR averaged 195 kJ/day, which is 30% lower than predicted from adult mass (82 g) and 2.7 times the measured basal metabolic rate. Nestling FMR (kJ/day) increased with mass (m in grams) according to the relation: FMR = -27.1 + 2.4m. Nestling FMR stabilized at about 160 kJ/day (82% of the adult level) by 3 weeks of age. Nestlings, which are adult sized when they fledge 30-32 days after hatching, grow relatively slowly. Their logistic growth rate constant (K = 0.226) is 30% lower than predicted from their mass and is equivalent to that of a tropical species of their size. Nestlings also develop endothermy much more slowly than expected and are unable to maintain adult Tb when exposed to 15°C for 30 min until they are 3 weeks old. In the field, nestling Tb fluctuated until about 3 weeks of age, apparently due to intermittent brooding by the adults. Nestlings metabolized an average of 3,853 kJ/bird over the nestling period (age: 0-31 days). Of the total, RMR comprised 46.8%, whereas activity, thermoregulation, and the heat increment of feeding combined accounted for 40.2%. The energy accumulated in growth amounted to 501 kJ, or 13% of the total. Gross growth efficiency (ratio of energy accumulated in tissue to total metabolized energy) is the lowest reported for any bird. Two factors contribute to low growth efficiency: (1) a slow growth rate, which may result in part from tannins contained in the nestling's partially acorn diet, and (2) thermostatic costs associated with a low nest-cavity Ta. These unusual physiological features indicate that energetic constraints may play an important role in influencing the costs and benefits of group living in this cooperatively breeding species.
URL:http://www.jstor.org/stable/1368232
Short Title:The Condor
Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith