Night at the Arboretum
Our resident Eastern Screech-Owl (Megascops asio). Note that while Screech Owls are nocturnal, they often come out during cool, sunny days to sunbathe! Photo: Jennie Kelly
What happens in the Arboretum at night? Read on to find out!
Everything comes to life at night! While it isn’t a Night at the Museum movie, Night at the Arboretum is sure to delight.
When night falls across the Arboretum and students venture out, more obscure aspects of campus come to light. For instance, did you know that three bat species reside in the Arboretum? A 2017 bat acoustic survey conducted on campus revealed some interesting details about our bat population. One-third of the nine bat species found in Pennsylvania can be found in our Arboretum. Bats are from the order Chiroptera and are the only flying mammals. Chiroptera translates from Latin as “hand-winged,” referring to bats’ finger bones, which act as wing struts and form the mechanics of their wings. While many bats are nectarivorous and important pollinators, all of Pennsylvania’s bats fall into the family Vespertilionidae, which are insectivorous, meaning they primarily eat insects. When they fly, bats produce a series of high-pitched noises, which echo off their surroundings, allowing them to fly and catch prey during the night. This echolocation can be picked up on sonar, which can be analyzed to determine bat presence and species identification.
The Hoary Bat (Lasiurus cinereus) is the largest in Pennsylvania and can be found here in the Arboretum. They are about 5.5 inches long, with a wingspread of about 15 inches. They have brown fur tipped in white, which gives them a characteristic ‘hoary’ appearance. Hoary Bats often roost in conifers high above the ground in more protected areas. They migrate to warmer climates in the winter, but return to Pennsylvania when the weather warms. The Big Brown Bat (Eptesicus fuscus), the second largest in PA, is also found here. These bats are about 4.5 inches long, with a wingspread of about 12.5 inches, and dark brown fur. Big Brown Bats are quite common, and can live anywhere from barns to hollow trees. Interestingly, they prefer to eat beetles and true bugs such as junebugs and stinkbugs, both of which are major agricultural pests. Instead of migrating south, these bats hibernate during the winter. The final bat species found in the Arboretum is the Silver-haired Bat (Lasionycteris noctivagans). These bats have white-tipped fur that gives them a silver appearance, and are about 4 inches long, with a wingspread of about 11.25 inches. The Silver-haired Bat is another migratory species, and prefers to live in the woods surrounding ponds and streams.
In addition to bats, several other nocturnal fauna also call the Arboretum home. A hollow tree on the south end of campus is home to an Eastern Screech-Owl (Megascops asio). This nocturnal bird is common in the suburban eastern United States, and finding pellets underneath a tree can hint at their presence in an area. Red foxes (Vulpes vulpes) have often been spotted near the Haverfarm and the area surrounding the President’s house. Red foxes are known for their cleverness, and can be found worldwide (the largest distribution of any land mammal, except humans!). The Arboretum also harbors several nocturnal insects, including fireflies and many species of moths. Fireflies (or lightning bugs, depending on where you are from) are luminous insects from the family Lampyridae. Fireflies are often found in the Haverford area during the summer months, where they can be spotted lighting up the night sky with their bioluminescence. Moths, on the other hand, are in the order Lepidoptera (like butterflies) and are important nighttime pollinators for plants including milkweeds, evening primrose, and bee balm. A healthy moth population has often been linked to increased native biodiversity and promoting honeybee populations, emphasizing their importance.
Ultimately, several critters in the Arboretum are most active at night; but what about our plants? Well, that’s a bit more nuanced. Let’s consider flowering plants (angiosperms). When a plant flowers, oftentimes the flower opens and remains open all day and night. However, there are some plants that either open or close their flowers at night. Wood Anemone (Anemone quinquefolia), a common spring ephemeral in the area, closes its flowers at night. Many Magnolia trees also have flowers that close at night. This plant behavior is known as nyctinasty, and can be a strategy for the plant to protect its pollen for a preferred pollinator, and to conserve energy. Nyctinasty can also include other plant movements in response to an absence of light, such as the folding of leaves or other leaf movements. Flowers that bloom at night are another example of nyctinasty. Common night-blooming flowers are Gardenia (Gardenia jasminoides) and Night-Blooming Jasmine (Cestrum nocturnum). This strategy is intended to attract nighttime pollinators like bats and moths, which is why the flowers of these plants are often heavily fragrant and light in color.
Many changes occur within a plant during the night, as their work continues even after the sun goes down. In fact, many tree species grow more at night than during the day, potentially as a result of lower water stress. Tree branches and plant stems can bend and move at night, often going through cycles of swelling and stiffening as water circulates through the plant. Recent scientific studies have further explored trends in plants at night, particularly as it relates to gas exchange, as a plant takes in carbon dioxide and releases oxygen. With the exception of CAM plants (plants, including cacti, pineapple, and some orchids, that have a specialized method of photosynthesis to adapt to dry environments), most plants keep their stomata (a plant’s pores that control gas exchange) closed at night to minimize water loss. However, some plants, including Picea (spruces), Betula (birches), and Rosa (roses) exhibit different behavior, where stomata remain open at night, altering gas exchange timing and potentially nutrient uptake.
Ultimately, nature comes alive at night, even though we might not see it as clearly as we do during the day. Whether going on a night walk or joining our nighttime events (such as our jack-o-lantern hike during our annual fall festival), I encourage you to take the time to intentionally notice things while outside at night. It might allow you to engage with some of the unique features of our environment that are only active during the night or those that exhibit interesting nighttime behaviors. Enjoy Night at the Arboretum!
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