The Project
The Kluane Red Squirrel Project is an interdisciplinary, large-scale field experiment designed to test the importance of food abundance to the ecology and evolution of red squirrels. The project is based in the southwest Yukon of Canada, where red squirrels have been studied extensively since 1987. In this part of their range, the seed of white spruce cones (Picea glauca) is a critical food resource for red squirrels. White spruce is a masting species, which means that these trees produce extremely high numbers of cones every 2-6 years with few cones produced in the intervening years. Individual red squirrels, therefore, are likely to experience both very high and very low levels of food within their lifetime. Research performed over more than 30 years has indicated that yearly variation in the abundance of spruce cones has important ecological and evolutionary consequences.
What we’ve Discovered
Red squirrels defend individual territories around a central store of food.
Squirrels ‘rattle’ at neighbours to defend their territory.
Each squirrels has a unique rattle call and they can recognize the calls of their neighbours.
Spruce trees produce bumper cone crops every 4 or 5 years. In a bumper cone year, squirrels can store 20,000 cones and these can last for 3-4 years.
Squirrels somehow know when there will be lots of cones in summer and increase reproduction in the spring before the cones are available.
Having more stored food allows a squirrel to reproduce earlier in the spring, live longer and produce more pups over its lifetime.
When a squirrel dies, neighbours quickly show up to steal cones. When a new squirrel takes over the territory, it inherits the old owner’s cache of food.
In some cases, mothers give up their territory to one of their pups and move to a new territory.
Female squirrels are in estrus for only a single day per year, but often mate with more than 7 males on that day to produce a litter of 3 or 4 pups.
Red squirrels do not hibernate, but they spend very little energy in the winter. On the other hand, they spend as much energy as elite athletes during reproduction and when hoarding cones.
Mothers assess how many neighbours they have by listening to their calls and use stress hormones to prepare their offspring to compete with lots of neighbours before they leave their mother’s nest.
Squirrels are more likely to try and steal food from new neighbours than long-time neighbours, and they live longer if they have fewer new neighbours.
Female red squirrels sometimes adopt an orphaned pup, but only if it is closely related to them.