Hollister-Smith, J.A., Alberts, S.C., and L.E.L. Rasmussen. 2008. “Do male African elephants, Loxodonta africana, signal musth via urine dribbling?” Animal Behaviour, 76, 1829-1841.

In male African elephants, musth, a period marked by increased aggression, serum testosterone, sexual activity, and urine-dribbling, is correlated with mating success (most males who sire a calf were in musth at the time of conception). Furthermore, age and size (which are highly correlated) are good predictors of mating success, as well, but males in musth have higher a social status than they normally do (regardless of age or size) due to their increased aggression. Because elephant males enter musth asynchronously, the dominance relationship between two males at any given time is subject to change.

Males do not enter musth until they are about 29 years of age (in the wild; in captivity, 14 years is the mean). Usually only males in good condition enter musth, and their body condition/weight visibly deteriorates during it. The signals in their urine, which could serve to ‘warn’ other males about the sender’s musth condition, are assumed to be honest signals because they are physiological byproducts. Fights between males can be deadly, so strong selection on this signal is expected: successful transmission and processing of the musth signals potentially allows receivers to avoid musth males. From previous research it was known that musth males “decrease their association with other males and nonmusth males actively avoid musth males” (Hollister-Smith et. al 2008).

The researchers who conducted this study wanted to investigate whether male African elephants could discriminate between the urine of male elephants in musth and those not in musth, and whether they could discriminate between the urine of males in early and late musth (the condition of the sender declines between these two times). They collected early-musth, late-musth, and non-musth urine from 5 donor males with the help of zoo staff. Donor males were known, from zoo records, to be of similar age and dominance/social status. Twenty-six elephant males were then presented with four samples simultaneously: early-musth urine, late-musth urine, non-musth urine, and a control of water and vanilla extract. These samples were poured directly into the subject’s enclosure at a minimum of 3 meters apart. No elephant was presented with its own urine, and in each trial, each urine sample came from a different male. Tested males were not in musth at the time of presentation. Video of the trials was also taken and scored for different behaviors.

They found that bulls who had been castrated gave significantly fewer flehmens than other males, but did not otherwise differ in behavioral response to the urine samples. Musth urine elicited significantly fewer flehmen responses than did non-musth urine, so the authors concluded that males could indeed discriminate between musth and non-musth urine, and that they were using their vomeronasal organ to perform this discrimination. Younger males responded significantly higher than did older males and displayed more avoidance significantly more avoidance behavior (vs. older males) to all urine types. Males who were subordinate to other males within their enclosures showed significantly more avoidance behaviors than dominant males. Furthermore, if the donor male had been previously housed with the subject male, the latter was significantly more responsive to the urine sample of that donor. Lastly, males who had been housed with other males (African or Asian elephants) performed significantly more flehmens than males who had not. The researchers did not find evidence of discrimination between early- and late-musth urine.

This study supports what we learned in class about the importance of the vomeronasal organ for odor detection/discrimination in vertebrates. This organ is used to detect less volatile molecules compared to those that are detected by the main olfactory system. This study also demonstrates how behavior (in this case, flehmen) can aid in the reception of an olfactory signal and how the signals in urine (perhaps incidentally) give the receiver information about the body condition/status of the sender (selection for this ability in male elephants presumably has important consequences for their social behavior and how they interact with other males).