Mayer Paul M, Smith Levica M, Ford Robert G, Watterson Dustin C, McCutchen Marshall D, Ryan Mark R
Office of Research and Development, US Environmental Protection Agency, 919 Kerr Research Drive, Ada, OK 74820, USA.
Oecologia. 2009 Apr;159(4):893-901. doi: 10.1007/s00442-008-1266-9. Epub 2009 Jan 15.
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 suggest a trade-off between nest crypticity and thermoregulation of eggs based on selection of nest materials by piping plovers (Charadrius melodus), a ground-nesting bird that constructs simple, pebble-lined nests highly vulnerable to predators and exposed to temperature extremes. Piping plovers selected pebbles that were whiter and appeared closer in color to eggs than randomly available pebbles, suggesting a crypsis function. However, nests that were more contrasting in color to surrounding substrates were at greater risk of predation, suggesting an alternate strategy driving selection of white rocks. Near-infrared 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. Thermal models and field data indicated that temperatures inside nests may remain up to 2-6 degrees C cooler than surrounding substrates. Thermal models indicated that nests heat especially rapidly if not incubated, suggesting that nest construction behavior may serve to keep eggs cooler during the unattended laying period. Thus, pebble selection suggests a potential trade-off between maximizing heat reflectance to improve egg microclimate and minimizing conspicuous contrast of nests with the surrounding substrate to conceal eggs from predators. Nest construction behavior that employs light-colored, thermally reflective materials may represent an evolutionary response by birds and other egg-laying organisms to egg predation and heat stress.
捕食作用会淘汰鸟蛋和鸟巢中显眼的颜色，而体温调节的限制因素则促使鸟类形成调节孵化温度的筑巢行为。我们展示的结果表明，基于笛鸻（Charadrius melodus）对筑巢材料的选择，在鸟巢的隐蔽性和蛋的体温调节之间存在权衡。笛鸻是一种在地面筑巢的鸟类，它们建造简单的、用鹅卵石衬里的巢，这种巢极易受到捕食者的攻击，且暴露在极端温度下。笛鸻选择的鹅卵石比随机可得的鹅卵石更白，颜色也更接近鸟蛋，这表明具有保护色功能。然而，与周围基质颜色对比更强的鸟巢被捕食的风险更大，这表明还有另一种策略驱动了对白色岩石的选择。巢中鹅卵石的近红外反射率高于随机可得的鹅卵石，这表明通过选择鹅卵石来控制热量存在直接的物理机制。用随机可得的鹅卵石建造的人工巢升温更快，并将热量传递给模拟鸟蛋，导致蛋比用笛鸻巢中的鹅卵石建造的巢升温更快。热模型和实地数据表明，巢内温度可能比周围基质低2至6摄氏度。热模型表明，如果不进行孵化，巢升温特别快，这表明筑巢行为可能有助于在无人照看的产卵期保持鸟蛋凉爽。因此，鹅卵石的选择表明，在最大化热反射以改善蛋的微气候与最小化鸟巢与周围基质的显眼对比度以保护蛋不被捕食者发现之间可能存在权衡。采用浅色、热反射材料的筑巢行为可能代表了鸟类和其他产卵生物对蛋捕食和热应激的一种进化反应。
