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NATURAL FERTILITY IN WHOOPING CRANES AND MISSISSIPPI SANDHILL CRANES AT 
PATUXENT WILDLIFE RESEARCH CENTER 

JANE M. NICOLICH,: USGS Patuxent Wildlife Research Center, 12302 Beech Forest Road, Laurel, MD 20708-4022, USA 

GEORGE F. GEE, USGS Patuxent Wildlife Research Center, 12011 Beech Forest Road, Laurel, MD 20708-4041, USA

DAVID H. ELLIS, USGS Patuxent Wildlife Research Center, 11410 American Holly Drive, Laurel, MD 20708-4019, USA

SCOTT G. HEREFORD, USGS Patuxent Wildlife Research Center, 11510 American Holly Drive, Laurel, MD 20708-4019, USA 

The first fertile whooping crane (Grus americana; WC) egg produced through natural breeding at Patuxent Wildlife Research Center (Patuxent) was laid in 1991. Prior to that time, all fertile whooping crane eggs were the result of artificial insemination. Since 1991, eight different whooping crane pairs al Patuxent have produced fertile eggs through natural breeding. Mean fertility averages over years for each pair range from 40% to 93%. Fertility rates for each pair also vary greatly between years, from 0% to 100% but the causes of the variance are unknown. Experiences with natural fertility in Mississippi sandhill cranes (G. canadensis pulla; MSC) have been similar. Annual natural fertility rates averaged from 21% to 89% and fertility averages for each of 7 pairs also varied greatly between years. Rearing methods have not determined success in natural breeding for either species. Both hand-reared and parent-reared pairs have been fertile. Wing condition, however, has been an important factor affecting natural fertility. Because artificial insemination (Al) generally results in higher fertility rates than natural breeding, Al should continue for some pairs. 

PROCEEDINGS NORTH AMERICAN CRANE WORKSHOP 8:170-177 

Key words: artificial insemination, Grus americana, Grus canadensis pulla, Mississippi sandhill crane, natural fertility, whooping crane.

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