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Nest Construction by a Ground-nesting Bird Represents a Potential Trade-off Between Egg Crypticity and Thermoregulation
MAYER, P. M., L. M. Smith, R. G. FORD, D. C. Watterson, M. MCCUTCHEN, AND M. R. Ryan. Nest Construction by a Ground-nesting Bird Represents a Potential Trade-off Between Egg Crypticity and Thermoregulation. OECOLOGIA. Springer, New York, NY, 159(4):893-901, (2009).
To observe thermoregulatory constraints and selections for nest building behavior that regulates incubation temperatures.
Predation selects against conspicuous colors in bird eggs and nests, while thermoregulatory constraints select for nest building behavior that regulates incubation temperatures. We present results that reveal a trade-off between nest crypticity and thermoregulation of eggs based on selection of nest materials selected by piping plovers (Charadrius melodus), a ground-nesting shorebird that constructs simple, pebble-lined nests highly vulnerable to predators and exposed to temperature extremes. Piping plovers selected pebbles that were whiter and closer in color to eggs than randomly available pebbles, suggesting color-matching to disrupt the egg pattern. However, nest and substrate color were unrelated to nest success, suggesting an alternate strategy driving selection of white rocks. Near-infrared (NIR) reflectance of nest pebbles was higher than randomly available pebbles, indicating a direct physical mechanism for heat control through pebble selection. Artificial nests constructed of randomly available pebbles heated more quickly and conferred heat to model eggs, causing eggs to heat more rapidly than in nests constructed from piping plover nest pebbles. Models that related nest and substrate (random pebbles) temperatures in the field corresponded well with our lab experiments, indicating a difference of 2-6° C between temperatures inside and outside plover nests. Thermal models indicated that nests heat rapidly, especially if not incubated, suggesting that nest construction behavior may serve to keep eggs cooler during the unattended laying period. Despite apparent thermal benefits of selecting whiter pebbles, piping plovers did not always select the whitest pebbles available, suggesting that nest-construction behavior is selected to match nest pebble color to egg color but simultaneously avoid conspicuous contrast with the surrounding microhabitat. Given behavioral similarities in other ground nesting shorebirds, nest construction behavior that employs light-colored, thermally reflective pebbles may represent a common evolutionary response by other ground nesting shorebirds to egg predation and heat stress.