Longer days trigger nature's activities

            Around this time each year – oftentimes even earlier – most of us are pining for budding trees, migrating birds, and even the appearance of flying insects. Those environmental cues are a sure sign that the cold of winter has retreated for another year and shorts-and-sandals season will soon be upon us. Even though we had a record warm February this year, it didn’t appease our desire for even warmer weather.

            Part of the reason for this feeling has little to do with the actual temperature and more to do with the short length of winter days. Those short days can lead to what many of us call the

Cartoon by David Chatowsky

winter blahs, and as days grow longer we are reinvigorated and start to feel happier.

            In ecological terms, the length of daylight in a given day is called the photoperiod, and it is an important trigger for all sorts of natural history events. We sometimes assume that the awakening of wildlife in spring is linked to warming temperatures, and for some species it is. But for many others, it’s the increasing photoperiod that launches these activities.

            Birds are the perfect example. They use an ancient part of their brain called the pineal gland to detect light and dark through their thin skulls. When the daylight length is just right, it triggers them to prepare for migration by doubling their food intake and becoming active at night, which is when most songbirds migrate. In laboratory experiments at the University of Rhode Island, researchers have artificially manipulated the photoperiod to which birds are exposed, which cues the physiological changes required for migration even if it’s the wrong time of year.
               Using daylight length as a trigger for migration isn’t always a good thing, however. Those bird species that do so are having the most trouble adapting to the changing climate. During years when spring comes late, those species arrive when it’s still too cold to raise a family; during years when spring comes early, they’ve missed out on the early-flying insects they need to fuel reproduction. The birds that combine day length with temperature in determining when to migrate seem to be responding better to climate change.

                According to Hope Leeson, a botanist at the Rhode Island Natural History Survey, many plants are also triggered by daylight length to launch the next stages in their life cycle. Norway maples in Rhode Island, for instance, are one of the earliest trees to sprout leaves each spring, even though in their native Norway the trees don’t leaf out until later in the season. That’s because the leaves are triggered to emerge by a certain photoperiod, which occurs in Rhode Island several weeks earlier than in northern Europe.

                The bloom time and growth of many flowers in the aster family are also regulated by day length. Their growth is delayed – when compared to many other local flowers – until the days are sufficiently long, and they don’t flower until the day length gets shorter again in the fall, regardless of the temperature.

                The longer days of spring also trigger reproduction in many species, from green frogs to mink, and other aspects of some animals’ life cycles, like growth rates and molting of fur, can also be affected. Many humans are influenced by it, too. As I told my wife the other day, I’ll take out the trash as soon as the sun comes up a little earlier.

This article first appeared in the Newport Daily News on March 17, 2018.