BEACON Center for the Study of Evolution in Action

Most birds possess a uropygial gland that produces a secretion, preen oil, that contains volatile compounds that may transmit
information about individual attributes. However, the ability of passerine songbirds to discriminate among the odors of different
individuals has not yet been demonstrated. We tested whether dark-eyed juncos (Junco hyemalis) could discriminate among preen oil odors from 1) conspecifics and heterospecifics; 2) male and female conspecifics; 3) conspecifics from same or different population or subspecies; and 4) males with large or small plumage ornaments. Our evidence suggests that juncos can discriminate between the odor of conspecifics and heterospecifics. In 2-way choice tests between conspecific odors, both males and females spent more time
with male preen oil. Subjects did not discriminate between odors of individuals from their own population or a different one, and no relationship was found between choice and plumage ornaments. Unexpectedly, females spent more time with the odor of males with smaller body size, regardless of population of origin. This result was especially surprising because an analysis of preen oil volatile compounds revealed that the odors of smaller males were less ‘‘male-like’’ than the odors of larger males. We conclude that songbirds are able to detect odors from preen oil as shown by their ability to distinguish odors arising from males and females. They may also be able to distinguish among individuals of varying body size. Key words: birds, chemical communication, mate choice,
odor preference, olfaction, passerines, preen oil, Y-maze.

Songbird preen oil contains volatile and semivolatile compounds that may contain information about species, sex, individual identity, and season. We examined the relationship between testosterone (T) and the concentration of preen oil volatile and semivolatile compounds in wild and captive dark-eyed juncos (Junco hyemalis). In wild males and females, we observed an increase in volatile compound concentration early in the breeding season. This increase mirrored previously described seasonal elevation in T levels in wild males and females, suggesting a positive relationship between hormone levels and preen gland secretions and a possible role for those secretions in signaling receptivity. In females, the highest concentrations of most compounds were observed close to egg laying, a time when steroid hormones are high and also the only time that females respond to an injection of gonadotropin-releasing hormone with a short-term increase in T. In a study of captive juncos held on short days, we asked whether the seasonal increases observed in the wild could be induced with experimental elevation of T alone. We found that exogenous T stimulated the production of some volatile compounds in non-breeding individuals of both sexes. However, of the 15 compounds known to increase significantly during the breeding season, only four showed a significant increase in concentration in birds that received T implants. Our results suggest that testosterone levels likely interact with other seasonally-induced physiological changes to affect volatile compound concentrations in preen oil.

A “DNA barcode” is a locus at which conspecifics show a consistent level of sequence variation that is much lower than that found among species, and therefore could be useful for species identification (Hebert et al. 2003; Hebert et al. 2004). The COI locus has been suggested to be such a barcode, but critics have commented that closely related sister taxa have not been adequately sampled to show whether this locus can be used to differentiate species that may have diverged recently or very quickly (Moritz and Cicero 2004).

Several studies have suggested a greater role for olfactory cues in avian social interactions than previously recognized, but few have explicitly investigated the effect of odor on parental behavior. We present results from a preliminary study in which we applied hetero-and conspecific preen gland secretions, which are known to contain volatile compounds, to the nests and eggs of incubating female dark-eyed juncos Junco hyemalis.

Background Though genomic-level data are becoming widely available, many of the metazoan species sequenced are laboratory systems whose natural history is not well documented. In contrast, the wide array of species with very well-characterized natural history have, until recently, lacked genomics tools.