Gas conductance and metabolism of shorebird eggs: variation within and between species

Fresh egg mass (M0; g), water vapor conductance of the egg shell (GH2O; mg.[Torr.d]-1), and neonate mass (Mn; g) were measured in the ruff (Philomachus pugnax), common redshank (Tringa totanus), northern lapwing (Vanellus vanellus), black-tailed godwit (Limosa limosa), and Eurasian curlew (Numenius arquata). In addition, the development of embryonic O2 consumption (MO2; ml.d-1) and CO2 production (MCO2; ml.d-1) were measured in these species, except the ruff. In northern lapwing and black-tailed godwit eggs the coefficients of variation for GH2O were 3.8 and 2.3 times higher, respectively, than those for M0. In these two species only about 10% of the variation for GH2O was attributable to M0, and about 77% to differences between clutches, suggesting a strong maternal component. In the northern lapwing, embryonic MO2 plateaued prior to internal pipping, but not in the common redshank and black-tailed godwit. The latter result is in contrast to embryonic patterns previously described for other precocial species. In shorebirds the occurrence of an embryonic MO2 plateau is not related to the neonatal level of cold-induced thermogenesis.