Why would beavers be battling with nearby wood ducks? It might just be a general grumpiness with the long, dark winter approaching. Allison Shelley/Getty Images/TNS
A thought-provoking behavioral question came via Dan from Delmar, New York, who noticed an imbalance between a beaver and some ducks in a pond near his house. These two typically live in a symbiotic relationship (more on that later), so Dan’s question came after he witnessed the beaver becoming aggressive toward the ducks and chasing them out of the pond.
In late October we can all get testy with our neighbors, but this isn’t even an election year for beavers! So why is their demeanor changing in the fall?
There is an impending darkness in the life of a beaver right now, both figuratively and literally. With the literal shortening of days – the shorter photoperiod, or amount of daylight – beavers have less time to be active and prepare for the figurative darkness, in the form of a dearth of food. That puts a lot of pressure on any beaver trying to gather food, usually in the form of branches with bark, twigs, and leaves that they’ll eat before snow and ice make those tasks difficult or impossible. The ducks that Dan observed being chased by the beaver were wood ducks. They don’t directly compete for any food sources, but the aggression observed was most likely a result of stress from the season rather than any perceived competition. You know how when you are cooking, any other person in the kitchen can be aggravating, even if they are “helping”? It is probably just like that.
On the flip side, it wouldd do the ducks well not to upset a beaver as a neighbor because there is evidence that beavers have a positive influence on the breeding success of several species of ducks. While many people view beavers as a nuisance, their roles as “ecosystem engineers” are remarkable and important. Perhaps the best known beaver engineering feat is their dams, which create wetlands and eventually homes for a wide variety of species. Most trees flooded from the dams will die, and in turn become food for insects, then attract woodpeckers that will first eat those insects, and then make a nest in the tree (woodpeckers are primary cavity nesters). In subsequent years those cavities will be used by ducks, especially wood ducks (known as secondary cavity nesters). Your naturalist word of the week is commensalism: a symbiotic relationship in which one species benefits while the other species is not affected.
A 2008 study by Petri Nummi and Anna Hahtola from the University of Helsinki found that “beaver ponds harbored more resources, i.e. aquatic invertebrates than undisturbed waters, and invertebrate abundance was reflected as enhanced teal (duck) brood density.” The habitat created by beavers was shallower, making it better for ducklings, and even lowered brood mortality (how many die from each clutch of eggs).
So as we face an impending darkness (shorter days), keep Dan’s beaver in mind as you balance anxiety and aggression with neighbors (or family). Your typically symbiotic relations may be tested, but hopefully you’ll remember the brighter days ahead and those relationships will endure, be they mutualistic or commensalistic.
Depends on your definition of ‘who?’
Owls are one of the most common bird families that we get questions about, bested only by hummingbirds. I’ve written before about the common nocturnal noises, and the various hoots coming from great horned, barred, and saw-whet owls, but Geoff from Arrowsic asked a fun question, wondering if anyone has been able to translate what these various noises all mean. While we’ve got a long way to go before discovering the Rosetta Stone of owl vocalizations, we do know about a few sounds, and when, why, and which owls make them.
As a refresher of common owl songs, helpful mnemonics are: great horned owl says “Who’s awake? Me too”; barred owl sounds like “Who cooks for you? Who cooks for you all?”; and northern saw-whet owls resemble a truck backing up, giving a pulsing “toot toot toot.” We define a bird’s song as a vocalization used to attract a mate or defend territory, and all of these above aides are typical representations of each owl’s song. Other noises would be classified as calls, and can be remarkably varied.
An important call for readers to learn is the call that fledgling barred owls emit, typically in mid to late summer. This ear-piercing, almost blood-curdling, call is best described as a scratchy scream. (The noise sounds very similar to that of a barn owl, but that species is incredibly rare in Maine, with only one documented record in the past 30 years.)
My favorite noise to come from an owl was perfectly described by Geoff in his email: “One bird I’ve heard a number of times at night this fall (don’t laugh, I swear this is true!) sounds much more like a species that might be found in a south American jungle, not a pine/oak woodlot on the coast of Maine. It literally sounds like a bird or even a monkey with a call of “ooh-ooh-eee-eee-ahh-ahh-ahh-ahh!” over and over again.” That vocalization is known as “caterwauling” from a barred owl. This noise is typically heard from dueting pairs, but also is apparently given when they’ve captured a large prey item.
The breeding season begins early for owls in Maine, so winter is the time to listen for some of these songs. Keep your ears open and if you hear any noises you need identified, try recording them on your phone with a ‘voice recorder’ app or even taking a video and sending them along (although it is entertaining to see your onomatopoeia, like Geoff’s “ooh-ooh-eee-eee-ahh-ahh-ahh-ahh!”).
Do you have a nature question for Doug? Email questions to ask@maineaudubon.org and visit www.maineaudubon.org to learn more about birding, native plants, and programs and events focusing on Maine wildlife and habitat. Doug and other naturalists lead free bird walks on Thursday mornings at the Gilsland Farm Audubon Sanctuary in Falmouth.
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