EGG‐LAYING, INCUBATION AND HATCHING OF THE COMMON GULL (LARUS CANUS).

• Published in: Ibis
• Main Author: Barth, Edvard K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1955
• Subjects: Larus canus
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1955.tb01909.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1955.tb01909.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1955.tb01909.x

Summary. Eggs in 3‐egg clutches are identified as a, b and c , those in 2‐egg clutches as a and b . Egg‐laying can take place at all times of the day, but at least 50% of b, c and b s are laid between 1200 and 1700 hours. The average time between the laying of a and b , 46 hours, differs significantly from the 53 hours between a ´ and b ´ but not from the 47 hours between b and c. The average time between the hatching of eggs a and b was four hours, between b and c 17 hours and between a ´ and b ´ six hours. Out of 77 nests, eggs hatched out of the order in which they were laid as follows: a‐c‐b in four, b‐a‐c in nine, b‐c‐a in three, c‐a‐b in two, b ´‐ a ´ in four, a ´ and b ´ at the same time in two. Incubation usually began when the last egg had been laid, and lasted on the average for 25 d. 22 h. (extremes 24 d. 1 h. and 28 d. 4 h.). Eggs a and b have a significantly shorter incubation period than c , but a ´ and b ´ does not differ significantly. On the average, egg b was laid 46 hours after a and hatched four hours after it, c was laid 47 hours after b and hatched 17 hours after it; b‘ was laid 53 hours after a ’, after which 24 hours of “casual brooding” occurred, and b ‘ hatched six hours after a ’. Since “casual brooding” can postpone the beginning of actual incubation, consequent hatching of b ‘ can be postponed until at least 291/2 days after it is laid. If nests got wet for long periods they cooled, so that much rain will probably lengthen the incubation period. In several nests the temperature was recorded continuously with instruments. Examples are given of the relation of nest temperatures to egg‐laying and the early brooding period. During the incubation period the highest recorded nest‐temperature (at the top of the eggs) was 43° C. The embryo does not appear to develop at normal speed below 30° C., which is seldom reached before the last egg in the clutch has been laid.