Avian Conservation and Ecology (Dec 2015)

Sex ratios of Mountain Plovers from egg production to fledging

  • Margaret M. Riordan,
  • Paul M. Lukacs,
  • Kathryn P. Huyvaert,
  • Victoria J. Dreitz

Journal volume & issue
Vol. 10, no. 2
p. 3


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Skewed sex ratios can have negative implications for population growth if they do not match a species' life history. A skewed tertiary sex ratio has been detected in a population of Mountain Plover (Charadrius montanus), a grassland shorebird experiencing population declines. To study the cause of the observed male skew, we examined three early life stages between egg and fledgling in eastern Colorado from 2010 to 2012. This allows us to distinguish between egg production and chick survival as an explanation for the observed skew. We examined the primary sex ratio in eggs produced and the secondary sex ratio in hatched chicks to see if the sex ratio bias occurs before hatching. We also determined the sex ratio at fledging to reveal sex-specific mortality of nestlings. The primary sex ratio was 1.01 (± 0.01) males per female. The secondary sex ratio consisted of 1.10 (± 0.02) males per female. The probability of a chick surviving to fledging differed between males (0.55 ± 0.13) and females (0.47 ± 0.15), but the precision of these survival estimates was low. Sex ratios in early life stages of the Mountain Plover do not explain the skewed sex ratio observed in adults in this breeding population.