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Gabriela Franzoi Dri collecting field data. Photo by Stephen Traylor
Written by Gabriela Franzoi Dri
We all know that farmers try to predict if the coming season will produce a good crop based on spring weather. But have you ever wondered if squirrels can predict if this will be a good or poor acorn year? This is very intriguing because trees produce variable seed quantities each year – a process we call “mast-seeding” – and squirrels certainly would benefit from knowing when food will be more abundant. But can squirrels and many other small mammal seed predators, like chipmunks, mice, and voles, predict when and where mast-seeding will happen specifically? This is one of the questions I aimed to answer in my research to earn a PhD in Wildlife Ecology at the University of Maine, co-advised by Dr. Mac Hunter and Dr. Alessio Mortelliti.
Holt Research Forest. Photo by Gabriela Franzoi Dri
For this project, we took advantage of the unique 36-year dataset on small mammals and seeds provided by Holt Research Forest. In the summers from 1983 to 2019, Jack Witham set 144 trapping stations with small mammal live-traps and seed traps to estimate the rodent and seed abundance. With this large dataset, we evaluated whether small mammals predicted where there would be a higher abundance of seeds in the forest by establishing their territories in those areas. We expected that they would because previous studies have found that some squirrels can predict when a mast-seeding year would happen and start reproducing earlier in the season as anticipatory behavior. So we hypothesized that the chemical and visual cues such as pollen, flowers, and unripe seeds would trigger small mammals to find territory in areas that would soon have a higher abundance of seeds.
A trap station at Holt Research Forest includes two Sherman traps to live-capture small mammals and one seed trap. Photo by Gabriela Franzoi Dri
It turns out that small mammals did not change their territories based on upcoming seed availability. This may be because other factors apart from uncertain food availability play a role in establishing territory, such as cover from predators and mating opportunities. Another possibility is that territory establishment may be determined by immediate conditions – animals responding to food availability day by day and not to predictions based on environmental cues.
This research using data collected at Holt Research Forest, one of the longest and most detailed datasets on small mammals and seeds, advanced our understanding of how animals respond to mast-seeding events by rejecting a key hypothesis that animals selected habitats based on future resource acquisitions.
Gabriela’s study was published in the peer-reviewed journal, OIKOS, in August 2022.
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