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1 September 2009 Egg Laying, Egg Temperature, Attentiveness, and Incubation in the Western Bluebird
Jennifer M. Wang, Wesley W. Weathers
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We present the first detailed information on egg laying, egg temperature (Tegg), and development of attentiveness and incubation in Western Bluebirds (Sialia mexicana). We used miniature infrared CCD video cameras to record egg laying at three nest boxes and validate attentiveness measurements derived from Tegg in seven other nests. Females entered the nest box on egg-laying days between 0522 and 1037 hrs PST and laid an egg on average 11.4 ± 4.3 min later (n  =  11). Warm weather early in egg laying often elevated Tegg above physiological zero (27° C), despite low parental attendance. Females often began roosting in the nest box 2–3 nights before clutch completion, and most birds began steady night-time incubation with the penultimate egg. Attentiveness, mean Tegg, and number of minutes Tegg exceeded 27° C reached their highest values 1 day or night after clutch completion. Western Bluebirds exhibit gradual onset to incubation that is attributable to vagaries of weather and varying patterns of parental attentiveness.

Jennifer M. Wang and Wesley W. Weathers "Egg Laying, Egg Temperature, Attentiveness, and Incubation in the Western Bluebird," The Wilson Journal of Ornithology 121(3), 512-520, (1 September 2009).
Received: 8 September 2008; Accepted: 1 February 2009; Published: 1 September 2009

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