Shifting seasons

Tim Iverson

(11/2017) Seasons come and go. Warm summer sun and verdant greens fade into the vibrant reds and oranges of fall. White snow capped fields yield to bright ephemeral spring flowers. With seasonal changes organisms have evolved different ways to survive. Animals have three options when confronting this prospect: adapt, hibernate, or migrate.

The first way to survive the winter months is to just adapt. These animals will have to make serious changes and work even harder during these tough winter times to survive. Deer and rabbits forage underneath snow cover to find food. If the temperature drops significantly deer will gather close together in dense tree stands using body warmth to wait out the cold. Shrews, which during the summer months eat primarily berries, mushrooms, and insects, will hunt exclusively for prey during the winter. Beavers and squirrels will store up food during the summer and fall months to snack on throughout the long cold winter. Most animals add an additional layer of fat that helps to insulate the body against the cold. Many animals will shed their fur or molt their feathers and grow a thicker winter coat to assist in insulating body heat. Some animals, like the mountain hare, will even change the color of their coat. By changing the color of their coats from brown to white they can now camouflage in the snow to avoid getting preyed upon by others. Many animals choose to forgo winter altogether as weather can be harsh and food is scarce.

Hibernation is an evolutionary adaptation that helps mammals and reptiles survive winter. During hibernation metabolic rates essentially come to a grinding halt. Heart rate can drop to as little as 3% of normal rate. For example, a chipmunk will go from 200 to 5 heartbeats per minute during hibernation. Breathing can slow to half (or more) of the usual rate, with some species stopping breathing entirely. Every living thing burns energy all the time simply by being alive. It takes energy to walk, sleep, breathe, and even to think! Mammals spend a lot of their energy just regulating body temperature. We eat to get enough energy to do all these things. During the winter plants stop producing fruit and food is all around a lot harder to come by. So, in order to conserve energy reptiles and some mammals will hibernate.

Hibernation isn’t very similar to sleep. Animals virtually lose all consciousness and are nearly impossible to wake up. When they do eventually come out of hibernation they often exhibit signs of sleep deprivation, and may need to dedicate a substantial portion of time to sleep. The primary difference between sleep and hibernation basically boils down to what the body is doing. During sleep there are minor physiological changes to the body, it’s mostly mental change. It’s also very easy to wake up from sleep, whereas hibernation it’s nearly impossible making these animals susceptible to predation. During hibernation brain activity is actually very similar compared with normal active brain activity. Hibernation just brings animals to the lowest possible metabolic rates they can stand so they require nearly no energy. Animals are given natural cues to start hibernating when the days get shorter and colder. This is the same time that other animals, mostly birds, begin travelling south.

When the weather turns migratory animals pack up shop and relocate to more suitable environments for a few months. The longest migration belongs to the Arctic Tern, which spends summers breeding in the Arctic and over-winters in Antarctica, encompassing the globe for a whopping 25,000 mile round trip journey! The switch that flips indicating when a bird should head south is initiated by a few factors. Shortening daylight hours, cooler temperatures, dwindling food supplies, and genetic factors are all cues that tell a bird when it’s time to go. Migratory birds can cover thousands of miles during a single trip. They seem to intuitively know the way to go. Even first year birds who have never made the trip before can manage on their own. Biologists have wondered how that can be, and the best research indicates that they utilize landmarks, the sun and stars, and the Earth’s magnetic field.

How do these plants and animals know when to do this? That’s where a type of ecology, known as phenology, comes in. Phenology is the study of changes in seasonal timing, it literally means the study of appearance. Animals take their cues from the food availability, sun, and weather pattern changes. This is the mechanism that tells them what to do and when. Other animals like hibernators and long distance migrators are on a cyclical clock that cues them into when it’s time to wake up or move along. In either instance, decades long research indicates that for some species these annual events are occurring earlier and earlier every year. The UN’s Intergovernmental Panel on Climate Change (IPCC) released a report in 2007 showing that spring is arriving by about 2.3 to 5.2 days earlier per decade in the last 30 years. The findings show that the seasonal timing that ushers in plants and animals is accelerating across the globe. These new arrival times for plants and animals aren’t always syncing up potentially leading to complex problems down the road.

Plants are putting out buds earlier every year, insect populations are emerging sooner than they historically should, and many birds are advancing the timing of their annual migrations. While they all seem to be reacting to climate change by advancing these seasonal behaviors, they are not doing so at the same rate. By falling out of sync food sources are not readily available for these insects or animals at critical times, like breeding or migrating seasons. The Great Tit, a European songbird, relies on caterpillar availability each spring to feed its young. These caterpillars have emerged earlier with warmer temperatures, but the Great Tit hasn’t advanced their egg-laying causing a mismatch between the two species. As a result, the hatchlings are missing peak food availability and less hatchlings are surviving to leave the nest.

Changes like this are prevailing trend across the globe. It signals potential problems for more than just wildlife, as it could dramatically impact human food production. Pollinators are needed when agricultural plants begin flowering. Fisheries depend on annual migrations that affect production and livelihoods. Unfortunately, the impacts of changing climates are already being experienced far and wide. By observing appearances of these cyclical events we can get a pretty clear picture of what’s going on in the world around us. Phenology can help researchers, policy makers, and people be better decision makers and agents of positive change. Citizen science participation can help researchers and policy makers. By helping track phenology and submitting findings individuals can help collect data that will help shape information and policy. Interested parties can explore options through Project BudBurst (budburst.org) by monitoring and observing plants, transcribing old weather logs through Old Weather (oldweather.org), or monitoring ice conditions through IceWatch USA (natureabounds.org/icewatch_usa.html).