Hagelin, J.C., & Jones, I.L. (2007). Bird odors and other chemical substances: A defense mechanism or overlooked mode of intraspecific communication? The Auk, 124(3), 741-761.

In this article, Hagelin & Jones present a review of experimental evidence suggesting that olfactory cues may be much more important to birds than previously thought. The focus of the paper is on two adaptive functions for olfactory signaling in birds: interspecific chemical defense and intraspecific chemical communication. Some birds in the genus Pitohui exhibit compounds called batrachotoxins that come from their diet (similar to the poison in poison dart frogs). Other species exhibit uropygial gland secretions that can vary with sex, age and diet.

To examine the chemical defense hypothesis, the authors searched for evidence of toxic or unpalatable effects on predators, and a correlation of fitness with toxicity. Native predators of pitohuis, such as the green tree python and brown tree snake, react to natural concentrations of the toxin (Dumbacher, 1999). The two most toxic pitohuis exhibit bright orange and black patches that may provide a visual warning to predators.

The hypothesis of intraspecific chemical communication also has some experimental support. Petrels appear to use olfactory cues to locate their nest site (Grubb, 1973), and can distinguish between the odor of their own nest and a neighbor’s nest in a T maze. Antarctic Prions can discriminate the specific odors of their mates (Bonadonna and Nevitt, 2004). Male mallards with severed olfactory nerves exhibited fewer courtship displays, presumably because they could not detect seasonal female uropygial secretions (Jacob et al., 1979).

This article touches on several subjects discussed in our chemoreception lecture. There are several types of chemical signals mentioned in this article: 1) pheromones, or chemicals used for communication between conspecifics, as well as 2) allomones, which are chemical signals between species, such as predators and prey. In this article main hypotheses were that birds use chemical signals for both of these functions. Birds may use both modes of detection mentioned in the lecture. They may use olfactory reception to detect airborne chemicals, such as a parent finding a nest. When allopreening, birds may use contact reception to pick up chemical signals from their mates.

The article also discusses the production of chemical signals in birds. Birds produce chemical substances in the form of plumage odor, stomach oils, and blood. Our textbook defines two fundamental sources of pheromones: secretory glands and body orifices and organs involved in digestion and reproduction. Birds mentioned in this article have a variety of sebaceous glands including the uropygial (preen) gland, anal gland, salt gland, salivary gland and epidermal cells called sebokeratocytes. Sebaceous glands are flask-shaped or lobed. According to our textbook, old epithelial cells in these glands disintegrate to become a thick lipid-rich substance that volatile and nonvolatile pheromones become embedded in.

Our book does not discuss the possibility that birds use chemical communication. I think most ornithologists have overlooked this sensory system because they believed most birds have poor senses of smell and taste. It will be interesting to see if a new version of the textbook would include information on birds!