Sex determination of Eastern White-crowned Sparrows ( Zonotrichia leucophrys leucophrys ) using wing chord length

Abstract

Determining the sex of individuals in sexually monomorphic bird species outside of the breeding season is difficult. However, many monochromatic species exhibit sex differences in morphometrics, including wing chord length. For example, recent studies found that the Puget Sound ( pugetensis ) and Gambel’s ( gambelii ) subspecies of White-crowned Sparrow ( Zonotrichia leucophrys ) can be sexed reliably using wing chord length. However, the Eastern subspecies ( leucophrys ) has not been evaluated. We measured the wing chord length of Eastern White-crowned Sparrows migrating through the Long Point Bird Observatory and specimens from the Fatal Light Awareness Program to determine if this subspecies can be reliably sexed using wing chord length. We combined wing chord length measurements with molecular sexing to test the prediction that males have a significantly longer wing chord length than females. Unfortunately, we only captured one definitive-cycle female and were thus unable to test our prediction in definitive-cycle birds. Males in first-cycle plumage had significantly longer wing chord lengths than females in first-cycle plumage and, outside of an overlapping range (74–76 mm), this subspecies can be reliably sexed using wing chord length. Our results support the use of wing chord length as a tool for bird banders and researchers to determine the sex of Eastern White-crowned Sparrows in first-cycle plumage in the hand outside of their breeding season or in the absence of a cloacal protuberance or brood patch.

Keywords

• blood
• dna
• feather
• molecular sexing
• wing chord
• zonotrichia leucophrys