The wild animal realm is one in which a microscopist may never even think to focus on. Brookfield Zoo, Brookfield, IL, is the home to numerous exotic animals from all over the world. A collection of animal hairs from an array of animals at the Zoo was examined, and photomicrographs were made using polarized-light microscopy (PLM) and scanning electron microscopy (SEM). After a long proposal, and approval from the Zoo, a project was initiated that would benefit not only McCrone Associates, but the Zoo as well. The plan was to set up a display at the Zoo featuring the images of the exotic hairs; McCrone Associates would be acknowledged as the provider of the images.

What is hair? Webster defines hair as a slender threadlike outgrowth of the epidermis of an animal. Hair comes in an array of colors, textures, sizes, and shapes. There are two distinct parts, the hair bulb, or root, and the hair shaft. Just beneath the surface of the epidermis lie tiny cup-shaped pits within the fat of the scalp; these cavities are known as hair follicles. The hair bulb lies within the hair follicle; it is the structure that contains actively growing and dividing cells. As new cells are formed, they steadily push the previously formed cells upwards. Also within the follicle, lies the mid-follicle region. Here the actively growing cells die and harden, and consist of the protein, keratin.  Eventually these “scales” are pushed upwards, and out of the skin, creating the shaft.

There are three main regions that make up the shaft of the hair: the cuticle, cortex, and medulla. The cuticle is a thin translucent layer on the exterior of the shaft. Cuticle scales, formed as the hair grows outward and consisting of keratinized cells, are usually overlapping, non-nucleated, and pigment-free. The cortex is the main body of the shaft, and is composed of elongated, filamentous cells that grow parallel to the shaft. The cortex may also contain tiny air spaces called fusi, and even smaller pigment granules. The medulla is a hollow, cellular, central core that, when present, runs through the center of the cortex.  Its structure may be fragmentary, continuous, or discontinuous.  Medullas from lower animals tend to be very regular and well defined. These medulla types are known as uniserial or multiserial ladder, cellular or vacuolated, and lattice. The main function of the medulla is to provide protection and temperature stability by adding internal air spaces. The medullary index is also a valuable tool for species differentiation; it can be calculated by dividing the average width of the medulla by the average width of the cortex. However, the medulla may differ from one hair to another on the same species.

Why study hair? One reason is for animal identification; it is helpful to differentiate between animals of similar species. The scale pattern on a hair is one of the important identifying characteristics and can almost always be used as a “finger print”. Every species has its own scale pattern unique to them. Another reason why one may study hairs is for animal distribution; certain areas are surveyed to determine if a species is present in that area. A third reason why one may study hair is because it’s fun, it’s inspiring, and it’s educational too.

The animals reviewed here have been chosen because they are all either endangered or threatened in the wild. When this happens, a species survival plan (SSP) may be developed to help prevent the animal from becoming extinct. SSPs are cooperative breeding programs between zoos that aim to increase the captive population of endangered species.  Currently there are 87 SSPs covering 116 species throughout 183 zoos within North America. Brookfield Zoo has 44 endangered species within their collection.