Long-term effective population sizes of thick-billed murre colonies appear to be on the order of 104 pairs (see Appendix), whereas breeding ledges within colonies probably contain on the order of 10s of murres (see above).
In this study, we examine the relationship between egg size and posthatching growth in the Thick-billed Murre. To disengage any possible relationship between egg size and parental attributes, we randomly switched eggs among pairs, and then measured growth in mass and wing length of chicks from hatching until nest departure.
Only chicks that survived [greater than or equal to]15 d were included in our analyses because 15 d is the youngest age at which Thick-billed Murre chicks are known to depart the colony (Gaston and Nettleship 1981).
Gilchrist (personal communication), conducted simultaneously with our study, showed that over the whole season, roughly 8% of Thick-billed Murre pairs lost an egg or a chick to predation by Glaucous Gulls (Larus hyperboreus).