Washington, Nov 1 In American coots egg size matters when it comes to survival of the offspring, says a new study.

The study was conducted over two breeding seasons on small wetlands in the prairie-parkland region south of Minnedosa, Manitoba, Canada.

Researchers Wendy Reed and Mark Clark at North Dakota State University, Fargo, and Carol Vleck at Iowa State University, Ames, found that female American coots favour their largest offspring, even before they hatch.

In the study, they placed newly hatched chicks in foster nests. Their findings showed that chicks from a female's largest eggs survived better than their smaller genetic siblings.

This was true even though siblings were not raised together, nor raised by their genetic parents.

Egg size and other maternal investments vary even more among different mothers, but that did not matter for survival of the offspring.

"What matters is that an offspring is the largest among its genetic siblings. It doesn't mean that bigger is always better, but it does mean that being bigger than your brothers and sisters is important for survival," Reed said.

Often called marsh hens or mud hens, the 16-inch long American coots are known for their territorial and noisy, cantankerous habits.

Females lay 5 to 16 eggs per clutch and movement of broods among ponds is rare, which facilitates monitoring the survival of the young.

The study has been reported in the November issue of The American Naturalist. (ANI)