Julie C. Hagelin

BIRD ODORS AND OTHER CHEMICAL SUBSTANCES: A DEFENSE MECHANISM OR OVERLOOKED MODE OF INTRASPECIFIC COMMUNICATION?

Bi ds e i an chemical compounds, though ornithologists rarely consider them. Avian odors, for example, are readily detectable to humans in at least 17 avian orders and 80 genera (Table 1; data from Weldon and Rappole 1997). Scents consist of volatile chemicals, and birds embrace a remarkable diversity of aromas, such as the musky plumage of storm-petrels (Hydrobatidae; Jacob and Zisweiler 1982); the tangerine-like perfume of Crested Auklets (Aethia cristatella; Humphrey and Phillips 1958); the acrid, sour odor of Hooded Pitohuis (Pitohui dichrous) and Variable Pitohuis (P. kirkocephalus; Dumbacher et al. 1992); the sweet and dusty fragrance of the Kakapo (Strigops habroptilus; Butler 1989, J. C. Hagelin pers. obs.); and the foul stench of the Hoatzin (Opisthocomus hoatzin; see Weldon and Rappole 1997). Birds also produce a variety of substances consisting of larger, less volatile compounds. Frequently odorless, these occur in various forms, such as saturated fatt y acids of uropygial gland secretions (Jacob and Zisweiler 1982, Sweeney et al. 2004) or toxins sequestered in plumage or skin (e.g., Dumbacher et al. 1992). Human detection of an avian compound clearly does not mean that it is important to a bird, unless this has been verifi ed experimentally. Here, we focus on two major types of adaptive functions that have been proposed for a variety of odors and other chemical substances that birds either produce themselves or sequester from secondary sources. First, avian compounds may serve as a chemical defense. This includes protection against predators, ectoparasites, and microbes and can involve substances that act as an interspecifi c deterrent or signal (e.g., Cott 1947, Swennen 1968, Dumbacher et al. 1992, Mouritsen and Madsen 1994, Douglas et al. 2001, Shawkey et al. 2003). Alternatively, some authors posit that avian compounds function as an intraspecifi c chemosignal, similar to those found in other vertebrates, such as mammals (e.g., Balthazart and Schoff eniels 1979; review in Roper 1999, Hagelin 2007). Recently, birds have been shown to recognize conspecifi c body odor (Hagelin et al. 2003) and personal body odor or mate odor (Bonadonna and Nevitt 2004). Some chemical signatures are even individually specifi c (e.g., Bonadonna et al. 2003a, b, 2004, 2007). The use of chemical signals in intraspecifi c communication has the potential to fundamentally alter how we interpret bird behavior. The idea is relatively new and challenges the traditional view that birds predominantly respond to their world through sight and sound. Birds readily respond to chemicals derived 1Department of Biology, Swarthmore College, 500 College Avenue, Swarthmore, Pennsylvania 19081, USA; and 2Department of Biology, Memorial University of Newfoundland, St. John’s, Newfoundland, A1B 3X9, Canada Julie C. Hagelin1,3 and Ian L. Jones2 BIRD ODORS AND OTHER CHEMICAL SUBSTANCES: A DEFENSE MECHANISM OR OVERLOOKED MODE OF INTRASPECIFIC COMMUNICATION? The Auk 124(3):741–761, 2007

A tangerine-scented social odour in a monogamous seabird.

Social odours, conspecific chemical signals, have been demonstrated in every class of vertebrate except birds. The apparent absence is surprising, as every bird examined has a functional olfactory system and many produce odours. The crested auklet (Aethia cristatella), a monogamous seabird, exhibits a distinctive tangerine–like scent closely associated with courtship. Using T–maze experiments, we tested whether auklets preferred conspecific odours and whether they distinguished between different types of scent, two prerequisites of chemical communication. Crested auklets exhibited: (i) an attraction to conspecific feather odour; (ii) a preference for two chemical components of feather scent (cis–4–decenal and octanal), which we identified as seasonally elevated; and (iii) differential responses to odours, as indicated by a preference for auklet odour, an aversion to mammalian musk, but no significant response to banana essence (amyl acetate). Our results suggest that crested auklets detect plumage odour and preferentially orientate towards this stimulus. The striking and well–described courtship display that involves the scented neck region, the ‘ruff sniff’, provides a conspicuous behavioural mechanism for odour transmission and the potential for scent assessment during sexual selection. Although the importance and full social function of chemical signals are just beginning to be understood in birds, including crested auklets, social odours promise to reveal a largely unexplored and possibly widespread means of avian communication.

Castration in Gambel's and Scaled Quail: Ornate Plumage and Dominance Persist, but Courtship and Threat Behaviors Do Not

During the breeding season, testosterone in male birds is often linked to some secondary sexual ornaments, courtship behaviors, and intrasexual aggression. I examined the effect of castration on plumage expression in Gambels Quail (Callipepla gambelii), a species in which males are highly ornate, and in Scaled Quail (C. squamata), an unornamented species. Using male pairs, each consisting of a castrate and a control, I also assessed whether castration affected (1) the behavior of males, (2) the mating decisions of females, or (3) the outcome of male-male competition. Castration did not alter the plumage of male Gambels or Scaled Quail. In these species, and some other members of the avian order Galliformes, production of ornate plumage appears to be independent of testosterone. In contrast, castration reduced or eliminated courtship behaviors. Females almost never preferred castrated individuals. During male-male competition, castrates also exhibited lower rates of threat behaviors, which appear to be identical to those used during courtship. Castration did not, however, influence the outcome of male-male competition. Castrates of both species exhibited overt aggression (pecks, chases, displacement) and frequently won male contests. Such results suggest that certain types of aggressive behavior may be testosterone-independent. In both Gambels and Scaled Quail, male body size correlated positively with dominant individuals.