PHYSICAL AND BEHAVIORAL ASPECTS OF INCUBATION IN THE ARGENTINE GRAY RHEA (RHEA AMERICANA ALBESCENS)

GWENDOLYN JEANNE LEMIRE, Fordham University

Abstract

Field and laboratory studies were conducted at the New York Zoological Park, Bronx, New York, to determine the extent to which the incubating male rhea contributes to providing and maintaining conditions near optimal to embryonic development and the extent to which the eggs and the nesting site contribute to the total energetics of incubation.^ Two rhea nests were monitored daily, the first for the last 27 days of incubation to hatching, and the second for the initial 19 days until nest destruction. Temperature probes were placed on and in the eggs and at various positions in the nest. Temperatures on the surface of the eggs varied from 22.3 to 40.3(DEGREES) C. Internal egg temperature averaged 33.9(DEGREES) C for a nonviable embryo.^ Behavioral responses of the adult rhea to various conditions of incubation were observed on a daily basis. Inattentive periods averaged 20.8 minutes in Nest I (enclosed sunny field), and 10.5 minutes in Nest II (open, more shaded field). Most inattentive time occurred within a 23-26(DEGREES) C ambient temperature range. No nest inattentiveness was seen below 19(DEGREES) C, or during rain or at night. Incubating rheas were attentive an average of 97.3 per cent of a 24-hour period.^ Squat turns, resettlings, returns from inattentive periods, or preening by the male were usually followed by egg-rolling and nest-building before resumption of sitting. The hourly frequency of egg-rolling was 0.72 in Nest I, and 1.1 in Nest II.^ In the laboratory hatcher (37(DEGREES) C, 85% humidity), eggs were tested manometrically for O(,2) absorption and gravimetrically for CO(,2) emission. One day prior to hatching, the maximum O(,2) consumption was 0.26cc O(,2)/gxhr, or 1.24 cal/gxhr, and CO(,2) emission was 0.89 cal/gxhr. Rates for dying embryos represented approximately one-quarter of rates for eggs that hatched.^ Maximum heat transfer required for the incubating bird to maintain clutch conditions was calculated to be 98.79 kcal/day or 12.79 per cent of the male's heat production at rest. From approximately 11 days from hatching, the clutch produced enough energy to compensate for the male's contribution.^ Internal cooling rate of eggs in Nest I was 0.12(DEGREES) C/10min (SD = 0.43, N = 11), and under laboratory conditions, 0.83(DEGREES) C/10 min (SD=0.33, N=9), the difference due to the nonviability of the field egg, solar radiation, and the insulative properties of surround eggs and nest.^ Loss of weight from eggs has been found to be due nearly entirely to water loss. Rhea eggs averaged a daily loss of 1.57 g or 10.25 per cent of their original weight at the end of incubation. For each gram of water lost, 580 calories are expended. Evaporative cooling may be an effective protective mechanism from overheating when considered on a daily basis when water loss from the entire clutch may have considerable consequences for the incubating male which is often exposed to intense solar radiation.^ As the metabolic rate increased with incubation and evaporative water loss remains relatively constant until breathing begins, cooling represents proportionately less of a pathway for heat loss. Heat loss by radiation and convection become more significant with time. At pre-IP (pre-internal pipping of the inner membrane), when metabolism was approximately 1.0 cal/gxhr and water loss represented 910.6 cal/eggxday, 6.8 per cent of the heat produced was eliminated by water loss.^ Metabolic water was calculated (0.11 kcal of O(,2) consumed yields 1 g metabolic water) and increased with incubation, and represented approximately all water loss near the end of the period. ^

Subject Area

Zoology

Recommended Citation

LEMIRE, GWENDOLYN JEANNE, "PHYSICAL AND BEHAVIORAL ASPECTS OF INCUBATION IN THE ARGENTINE GRAY RHEA (RHEA AMERICANA ALBESCENS)" (1980). ETD Collection for Fordham University. AAI8020069.
http://fordham.bepress.com/dissertations/AAI8020069

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