Title

Predictions and quantitative tests of optimal time and temperature allocation during intermittent incubation

Date of Award

5-2002

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

F. Reed Hainsworth

Keywords

Incubation, Eggs, Foraging

Subject Categories

Ecology and Evolutionary Biology | Physiology | Poultry or Avian Science

Abstract

Tests of optimization models are often criticized when the qualitative predictions of general models cannot be falsified. However, adequate tests of specific models require both quantitative predictions and precise data. Precise modeling techniques for thermal transients permit prediction of the egg temperature ( T Eexit ) at which a bird should leave the nest to maximize percent time foraging ( P ) when constrained by incubation. Within an incubation cycle, [Special characters omitted.] , when t cool , t heat , and t equil are times for egg cooling, heating, and maintenance at a constant temperature, and τ is travel time. T Eexit values for 4 bird species were compared with those predicted by the model. Observed T Eexit values for approximately half of all incubation cycles did not maximize P (N = 243; 4 species combined). Variation in incubation patterns produced slightly different average egg temperatures for each species, possibly producing different embryo development times. However, average predicted T Eexit across entire incubation periods (egg laying to hatching), were the same as observed. Thus, birds may maximize long-term P by combining incubation cycles with variation in time components to compensate for non-optimal behavior. Time required for incubation reduced P from a theoretical maximum of 100% to 19.77% for Black-capped Chickadees, 28.06% for Yellow-eyed Juncos, 34.27% for Tree Swallows, and 39.4% for House Wrens. Additional optimization criteria were also considered. T Eexit to maximize the rate of net energy gain ( RNEG ) differed from observed for individual junco, wren, and swallow incubation cycles and entire incubation periods. T Eexit to maximize RNEG for chickadee incubation cycles differed from observed, but average optimal T Eexit was the same as observed for the entire incubation period. The chickadees' ability to achieve the predicted average optimal T Eexist is linked to superior nest insulation and food caching behavior. T Eexist to maximize foraging efficiency differed from observed for all species. Although tests for all criteria could be falsified for individual cycles, predictions for P for entire incubation periods could not be falsified. Critics of optimization modeling would consider this a panglossian, and thus flawed, result. However, it appears valid and is likely the result of attempts to balance reproductive effort with self-maintenance over long time periods.

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