Male butterflies do not have physical means to inflict harm to one another when it comes to territorial disputes. Instead, two or more males may stage “contests” with each other which often involve elaborate aerial chases. For example, a male that flies into the territory of another male will set off a pursuit by the resident male, resulting in both flying in circles around each other until one eventually gives up and is chased out of the territory. Normally, winners of the contests are the males that are able to endure the longest flights. An example of what these competitions look like can be seen from this video:
Researchers have been puzzled by what determines which male butterfly wins a contest. Some researchers have thought body size should determine who wins the contest. After all, isn’t being bigger always better? Turns out for many butterflies, it’s quite the opposite, with smaller butterflies of some species winning contests more. What about age? Shouldn’t the most experienced butterflies have better odds at winning? Again, the opposite is often true, with some studies finding younger males having better odds at winning competitions. How about motivation? Could some male butterflies be motivated by something that gets them revved up? Researchers from Stockholm University in Sweden seem to think so!
In a study conducted by Martin Bergman, Martin Olofsson, and Christer Wiklund from Stockholm University, male speckled wood butterflies were tested by observing the number of contest rematches won by males that were subject to a source of motivation: a female speckled wood butterfly. Females are a primary purpose to why males hold territories, so interactions with them before a contest was thought to serve as motivation.
The researchers staged their experiment in a series of steps. The first step consisted of introduced contests between two male speckled wood butterflies over a territory, or in this experiment, a sunspot. In total, 60 pairs of males were used to conduct this experiment. Males that won five consecutive contests were considered “winners” and given the status of being the resident male over the sunspot. Afterwards, winners were temporarily removed from the sunspot they just previously won.
|Get out of my sunspot! Photo by Martin Bergman.|
All males that lost the contests were considered “losers” and were split in to two groups. The first group was allowed to interact with a female for 30 minutes. Males in the second group were placed alone in a cage for 30 minutes. Afterwards, each male was allowed back to the sunspot, now vacant of the winner. After each of the losing males took over the sunspot, therefore claiming themselves as the new resident male, the winners were then returned to the sunspot. The return of the winners allowed rematches of contests. Researchers recorded contest duration and if the males that lost the first round of contests won their rematches.
Loser males that had the chance to interact with a female won 53% of rematches while loser males placed alone only won 17% of rematches. In other words, males that interacted with a female endured longer flights to win their rematch. Furthermore, these same males were more likely to claim the vacant sunspot.
|Male speckled wood butterflies|
will “fight” over a female (such
as this one)…doesn’t this
concept sound familiar? Photo by
Mark Colvin at Wikimedia Commons.
Butterflies prove to be more mysterious and complex than we typically expect. Not only can they express territoriality without true physical means to harm each other, but they appear to be influenced by motivation! So, next time you see two butterflies fiercely circling each other in flight, you now know they mean serious business.
Bergman, M., Olofsson, M., & Wiklund, C. (2010). Contest outcome in a territorial butterfly: the role of motivation Proceedings of the Royal Society B: Biological Sciences, 277 (1696), 3027-3033 DOI: 10.1098/rspb.2010.0646