SPINAR, S.M.; REED, W.L.; CLARK, M.E.; North Dakota State University; North Dakota State University; North Dakota State University: Sex ratios in the American coot (Fulica americana)

Several recent studies in avian ecology suggest that females are capable of controlling the sex of their offspring. It has been hypothesized that females increase their reproductive fitness by producing the sex with the highest likelihood of survival. One mechanism proposed for the control of offspring sex is non-random segregation of sex chromosomes caused by differential allocation of maternal steroids to eggs. With the advent of molecular sexing it is now possible to estimate primary sex ratios prior to development of visible differences in gonads or other morphological characteristics. American coots (Fulica americana) are a common water bird that are not sexually dimorphic as hatchlings, and anecdotal evidence from the field suggests that many of these populations are male-biased. The main objective of this study is to quantify the primary sex ratio in coot hatchlings and correlate sex with maternal androgen deposition in eggs. Preliminary results indicate that the population sex ratio does not differ from unity. Preliminary results also indicate that males hatch from larger eggs and are significantly larger than females at hatching. Previous studies have shown that hatchlings from larger eggs within a clutch have a higher likelihood of survival than hatchlings from smaller eggs. These prior results, in combination with these new data, suggest that the survival of hatchlings may be sex biased.