Seasons and Snapshot Wisconsin…
How seasonality influences where animals are located is a major scientific focus of Snapshot Wisconsin. Animals move around, so their distribution in space changes through time. Animals also tend to have different phenophases – characteristics associated with specific seasonal or annual environmental phenomena (think spring or fall migration) that can influence how often they are detected by cameras.
A classic phenophase found in mammal species is torpor or hibernation, and bears provide an excellent local Wisconsin example. Whether bears are ‘true hibernators’ or not is often debated. Compared to many smaller mammals that drop their body temperature to near freezing, bears scarcely depress their body temperature at all. Furthermore, small mammals tend to sporadically emerge from hibernation throughout the winter to pass metabolic waste and eat a little…bears do not. Most amazingly, bears can go all winter without eating or moving without substantial muscle atrophy: unlike humans or most other mammals, bears can synthesize new proteins out of the nitrogen contained in their urea. While other animals wake up to pass waste, bears turn this waste into new muscle tissue.
One way in which Snapshot Wisconsin can contribute to our understanding of bear ecology beyond measures of bear distribution or cub production is by providing information regarding the timing of when bears seem to be active. Bears are clearly more regularly photographed during summer and early autumn than during winter:
The pictures provide an indirect cue as to how bears are behaving and the timing of their hibernation. This information can be used to evaluate hypotheses regarding variation in bear hibernation behavior–for example, there is some evidence that bears living in close proximity to humans and human food sources enter hibernation later than bears primarily consuming wild foods.
Seasonal patterns in wildlife images can also provide useful population-level information. Let’s visualize the photographic rates of a species that does not practice hibernation, deer:
There is a less pronounced seasonal pattern (a large drop in June reflects a slightly unbalanced effort across the year–many cameras were being set up at this time in 2015). Still, there is a drop in late winter and early spring that is consistent with what we know about the annual population dynamics of deer in the state–most adult deer die during late winter, and late-winter abundance should always be lower than pre-winter abundance (for comparison, one can find estimates of deer abundance based upon harvest metrics here and here). The number of pictures taken during any one time period is subject to a lot of variation beyond changes in population size, and we do not imply that a 50% increase or decrease in the number of pictures corresponds to a 50% increase or decrease in the number of animals. However, the count and timing of pictures is an input for statistical models that can correct for other sources of variation and be used to formally estimate things like changes in population size.