Ardea
Official journal of the Netherlands Ornithologists' Union

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Drent R.H. (1965) Breeding biology of the Pigeon Guillemot, Cepphus columba. ARDEA 53 (3-4): 99-160
1. The breeding biology of the Pigeon Guillemot was investigated during the summers of 1959 and 1960 at a colony of 100-110 pair in British Columbia. 2. Full attendance at the colony was noted only in the morning hours, the birds withdrawing to the feeding grounds in the afternoon. Other than those incubating or brooding the birds spent the night at sea. 3. Retention of the mate, nest-site, and perch-site (beach territory) over the years was the rule. 4. In the portion of the colony intensively watched 30% of the birds were non-breeders. Yearlings and two-year olds were included in this group. Age at first breeding was not determined. 5. A preliminary description is given of breeding behaviour and comparisons with other auks drawn. 6. Data on egg-laying dates imply that each female tended to lay in the same relation to the colony mean date each year. 7. Laying-hatching intervals (normal clutch two, A egg 32 days, B egg 30 days, laying interval 3 days) implied some effective incubation to take place when the first egg is still alone in the nest. Use of thermisters showed that incubation by day was intermittent in the laying period, and became steady on the day following the laying of the second egg. Night incubation set in at the earliest on the succeeding night; in other cases no sooner than four days after clutch completion. 8. The sexes shared duties in incubation, but the incubating rhythm was complex. Once steady incubation had set in the eggs were covered some 95% of the time, the birds incubating by night in one uninterrupted shift ( 7 hours). During the day they incubated in shifts varying from 40 minutes to upwards of 17 hours, broken into bouts of quiet incubation (extending from 10 minutes to 10 hours) by brief excursions to defaecate, bathe and preen. 9. Temperature at the interface between upper egg surface and brood-patch did not reach the definitive level until the second egg had been laid, or soon thereafter. Mean for this definitive level was 39.4 C for one nest (51.5 hours' readings spread from day 11 to day 28) which compares with an adult body temperature of 40.6 C for incubating birds. 10. The nestling period averaged 35 days (range 29-39) and was not terminated by a starvation period. 11. Feeding, the rate of which was influenced by demands of the chicks, showed no distinct tidal correlation, and was restricted to the daylight hours. The male and female caught food items in equal amounts. 12. At least 80% of the food items brought to the young were fish, primarily blennies and sculpins. They included forms rejected by the chicks. The parents showed individual food preferences. 13. Growth rate resembled that in other hole-nesting nidiculous auks, being distinctly faster than that of the open or semi-open nesting Alca and Uria, the young of which leave the colony prematurely. 14. There was no difference in growth rate, fledging period, or fledging weight between chicks raised alone and those in broods of two. 15. At fledging the mean weight for 20 young was 411 g, comparing to a mean weight of 450 g for 53 adults. 16. Even though metabolic response to environmental temperature was already homoiothermous on the day of hatching, the chick was about one day old before it could maintain a stable body temperature even at moderate environmental temperatures. The dramatic improvement in thermoregulation during approximately the first 24 hours coincided with a sharp increase in basal metabolism from the 50% level to values corresponding to, or slightly in excess of, those typical for adult homoiotherms.


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