Red squirrels use alarm calls to warn others when predators are near – no surprise there. Lately, however, a discovery has put these little guys back into the news. The reigning hypothesis used to be that Red Squirrels used different calls, matched to different types of predators. Specifically, Red Squirrels had a tonal sound for aerial predators, and another barking sound for ground danger. However, Dr. Shannon Digweed of Grant MacEwan University in Edmonton, has a completely new take on what those sounds mean.
Digweed first became suspicious of the projection that Red squirrels warn others of danger when she realized they were mostly a solitary species. Red squirrels are loners except for the short period when they are mating with another. If mating is not involved, the squirrels tend to be very aggressive towards each other. She spent many months in the field following individually marked squirrels and recorded every vocal response. She even set up some predator experiments involving taxidermies. All this data concluded that the calls were not just for aerial or ground predators, but for ANY types of disturbances in the squirrel’s immediate area. The tonal sound is to indicate the squirrel is aware of the disturbance, and the bark is to indicate the continued detection of a disturbance. These disturbances can include the presence of other squirrels, non-threatening animals like deer, and actual predators.
Digweed concludes that different call types should not be related to language, ie that they have different meanings aimed toward other conspecifics. Rather, the red squirrel uses the calls to let the disturbance, whatever it may be, know that it has been detected and it is continuing to be detected.
Find the interview with Dr. Shannon Digweed here: http://www.cbc.ca/quirks/archives/09-10/qq-2009-10-31.html#3
Edit:
This study is very new with very new material, so information on how the solitary red squirrel uses alarm calls during mating season is unknown. The same is true of other squirrel species. Simply not enough information has been compiled to state conclusive results.
However, I can tell you that typically, red squirrels mate during February, March, June, and July, and the females typically raise 2 litters a year. Males know when females are in heat because of an odor they generate. A pack of males will chase a female for about and hour, and the female will typically mate with the largest male in the group. I would think that if a cestrus odor is being produced by a female that other red squirrels in the area probably abandon their alarm calls if they know the ‘intruder’ is a possible mate.
Posted by Bethany Rappleyea
This is a very interesting article. Altruism is very rare in nature and when it comes to solitary species even rarer. So I find Digweed's take on these squirrel's alarm calls very sensible. It is understandable that these species would make these noises to perhaps deter predators given that they are usually aggressive to begin with. I wonder if these disturbances persist through their mating season.
ReplyDeletePosted by Alliam Ortiz
It's interesting that no one has thought about the fact that the squirrels are solitary before. Digweed putting that into the equation came up with a great conclusion about their communication. Does this mean that their alarm calls aren't heard during mating season?
ReplyDelete-Tricia Carlson
I agree with Tricia. It is interesting/strange that no other scientists thought it was weird that they would be alerting other squirrels when they are solitary animals.... It does make better sense that the squirrels would alert the predators that they have seen them and that they still see them. Good article!
ReplyDelete-Sara Ku
I wonder why noone ever thought of that before. It seems like something that should have been so obvious. What about other species of squirrels? Have they been able to find any evidence of the same thing?
ReplyDelete-Emily Crete
It's strange that the vocalisations made by squirrels in the presence of predators were assumed to be alarm calls to warn others when it's known that squirrels are solitary animals. Why do the squirrels have one call for when they notice a predator and one for when the predator is present for a while?
ReplyDelete-Posted by Sarah Benjamin