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Introduction
Many mammal and bird game species have gender-based regulations that allow the harvest of specific sexes on designated days. For example, the white-tailed deer season is open for taking only of males (bucks) with the exception of designated “doe days” in which females may be taken. These regulations are valuable tools in wildlife management and conservation.
At the time of inspection by regulatory authorities, game carcasses often are rendered to a state in which sex is not grossly apparent. In the Wildlife Forensic Field Manual (Adrian (ed.) 1992), the author provides an excellent review of anatomical elements that assist with determining sex in a decapitated big game carcass and various avian species. Let us review some gross photographs and diagrams from the manual.
Sex Organs
Identification of the sex organs obviously would be the easiest way to identify the sex of a carcass. The external organs usually are cut away in the field dressing process. Internally, the uterus, oviducts, or ovaries may be inadvertently left behind in the caudal abdomen.
Penile Ligament
In male artiodactylids (Order of even-toed mammals), portions of the penile ligament may be left behind in the field dressed carcass.
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Here you can see the investigator pointing out the remaining portion of the penile ligament in a cervid. You can imagine how this structure might be left behind in when the carcass in field dressed. (Photo credit: Wildlife Forensic Manual 1992) |
Pelvis
There are numerous points of comparison on the artiodactylid pelvis to help determine sex. Investigators divide these points into five areas. These characteristics vary between big game species and maturity and require experience to reliably differentiate sexes. Investigators may maintain reference sets of pelvises of known age and species to assist with field identification.
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Cervical Vertebra
The sex of several species of artiodactylids may be determined by comparison of the cervical vertebra. To perform this technique, the soft tissue must be removed from the vertebrae and a transverse incision made through the column. Thus, this technique is more likely to be applied in the laboratory.
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Males lack the accessory articular facets as seen in the diagram on the left. (Diagram credit: Wildlife Forensic Manual 1992) |
Lower Legs
Numerous measurements may be taken of the bones in the distal limbs of big game species to provide supportive information about the sex of an animal. These measurements differentiate sex on the basis of males being larger than females. Application of this data requires the use of regional standards.
Avian Species
Similar guidelines are described in the Wildlife Forensic Field Manual (Adrian (ed.) 1992) for sex determination in field dressed waterfowl, pheasants, and turkeys. We will not review every aspect, but let us cover some basics.
Syrinx
The syrinx is the vocal structure of avian species. This structure may be left behind when the head is removed from a waterfowl carcass and can be palpated by inserting a finger through the thoracic inlet.
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The syrinx is a sexually dimorphic structure in waterfowl.
Under hormonal influence, the syrinx develops into a much larger structure in males.
You can imagine how this structure would palpate differently between sexes. (Photo credit: Wildlife Forensic Manual 1992) |
Skeletal Measurements
Various game species of birds have reference data compiled on size ranges of skeletal structures in males and females. Normally, the males are larger than females; however, significant overlap may occur. In mallard ducks, six measurements are used, including two sternal parameters, one scapular, one coracoidal, one pelvic, and one humeral (Adrian ed. 1992).
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This ruler is available from the Nebraska Game and Parks Commission and used for measuring the sternums of Ring-necked pheasants for sex determination. As with mallard duck parameters, overlap exists between hens and roosters. |
External Characteristics
Sexually dimorphic differences in plumage color and secondary sexual characteristics may aid investigators in determining sex based on partial carcass evidence, such as a pile of feathers or skin. In some species, such as mallard and wood ducks, differences in plumage color are striking and can be differentiated easily between sexes. Keys exist to help distinguish feathers of sexes from species that initially may appear very similar.
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This is an example of a feather key for Ring-necked pheasants used to differentiate back feathers. (Photo credit: Wildlife Forensic Manual 1992) |
Other species, such as turkeys, have pronounced secondary sex characteristics, such as beards and enlarged spurs.
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In some cases, it may be necessary to determine sex from blood or a butchered meat sample. In big game species, hormone analyses may be run on meat and blood samples to determine sex. These analyses are limited to animals that are in rut (males with elevated circulating levels of testosterone) and females with high circulating levels of progesterone (pregnant or having an active corpus luteum). More recent genetic methods are available, such as PCR amplification of genes on sex chromosomes.
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