Egg size in Australian brush-turkey Alectura lathami hatchlings
predicts motor performance and postnatal weight gain

ANN GÖTH & CHRISTOPHER S. EVANS

Canadian Journal of Zoology, 82: 972-979

Birds usually influence offspring survival by the amount of parental care they provide. Megapodes have evolved a different life history. Eggs are incubated by external heat sources, chicks dig themselves out of their underground nest and live independently of their parents. Egg size is one of the few means by which females can influence chick survival. We found that in the Australian brush turkey Alectura lathami (J.E. Gray, 1831), eggs and hatchlings varied considerably in size, with a ratio of 1.62 between the largest and smallest egg. Egg size was positively correlated with the hatchlings’ body weight and tarsus length. It also significantly predicted the chicks’ motor performance: chicks from larger eggs dug their way out of their underground nest faster, and showed a higher activity level when kept in a resting box and monitored by motion-detection software. The main advantage of reaching the surface more quickly is likely to be that such chicks will have more time to find suitable food, refuge, and a tree for roosting at night, while still feeding on their internal yolk reserves. Egg size also interacted significantly with body weight during the first ten months of life. A size advantage at hatching thus seems to have an immediate effect on motor performance and a longer-term influence on the ability to gain weight.