A squirrel leaps through the grass at Deering Oaks with an acorn in its mouth. Ben McCanna/Staff Photographer

In my last column, I talked briefly about some funny squirrel behavior brought to my attention by Forrest Dillon. As Forrest had guessed, the squirrel’s behavior (which I could relate to, with the disappearance of my pumpkins) was tied to a low amount of mast this year. Forrest and I clearly weren’t alone because quite a few people have written in, asking “what is up with the lack of acorns this year?” So, let’s take a deeper dive into the factors that create a mast year.

Mast is a collective term for seeds and fruit produced by trees and shrubs, and the amount that is produced varies from year to year. We can oversimplify this by thinking about a garden: you (or your gardening friend, we all know that one person…) put a ton of effort into watering, weeding, etc., all to get the greatest yields possible, be it vegetables or flowers. Each year, with the same amount of control, you can yield similar results. But in nature, each year can be quite different based on the availability of nutrients, the weather, predators, and more.

A mast year (also called mast seeding) is one in which there are mass amounts of mast. Interestingly enough, we still don’t know much about why plants have these banner years. While it is easy to link a garden’s success or failure to resource availability (sure, my cucumbers would have done better if I ever watered them), many trees apparently have a very poor connection to overall resources during mast years. For example, there is a very low correlation between weather or rainfall and the amount of acorns that are produced in a year. There are always exceptions, of course: nature doesn’t like to be put into boxes that are easily explained in the Sunday paper.

A squirrel gathers acorns in a yard in Saco in 2020. The supply of acorns changes each season because of many factors, from weather to predators. Shawn Patrick Ouellette/Staff Photographer

Some studies have shown that stressors like a spring frost, or a summer drought, can cause mast seedings. This leads to a common theory that these plants are overproducing seeds when they are stressed, in a last ditch effort to make sure they get as many copies of themselves out there as possible. Go out with a bang!

Along those lines, sticking with our oak-acorn example here, we get to another theory that is called “predator satiation.” This is a type of adaptation that prey will adopt in an attempt to essentially overwhelm their predators. Applying that concept to plants, during a mast year, an oak will produce so many acorns that there will be more than all of its predators are able to eat. There are a lot of predators out there that eat acorns, from squirrels to deer to blue jays, so during non-mast years, very few acorns survive.

Given the irregularity of mast years, it would make sense that every few years a tree could attempt this technique, making so much food for its predators that they are overwhelmed and the extra seeds survive and germinate. Then, of course, the result is often that those predators will have high reproduction rates, setting us up for years like the 2018 “squirrel-mageddon.”


Getting back to this year, it is not a mast year, at least not for our oaks, so there are not many acorns on the ground. We have seen a couple of big mast years over the last decade; the fall of 2019 left a slippery carpet of round acorns all over the forest floor in Maine. Hopefully many of those survived and are slowly poking up from the ground, reaching toward the sun, and in another 20 to 30 years will produce their first acorns.

Why does that snowflake have wings?

A quick lesson for this week. There’s an insect that I want every Mainer to learn, and teach to a friend. I’ve been getting a ton of “what’s this bug?” emails, so let me introduce you to the woolly aphid. These tiny aphids get their name from cotton-like filaments that extend behind them, off their bodies, that has also earned them a variety of colloquial names like “fluff bugs,” “snow bugs,” “fluffer fairies,” and “poodle flies.” Often they just look like early snowflakes with wings.

There are a lot of species, even a few dozen genuses, within the larger Eriosomatinae family, the collective family of things we call woolly aphids. An interesting fact about them is that they typically only have one host plant where they’ll lay their eggs (the same way that monarch butterflies only lay eggs on milkweed), and knowing which host they use is generally the best way to identify them.

While some of the aphid species can be considered pests because of the damage they cause on certain hosts, they are harmless to humans and overall just another fun piece of Maine’s biodiversity to appreciate. Pretty soon we may be seeing real snowflakes instead of these winged ones, but keep an eye out for them while you’re enjoying the outdoors.

Do you have a question for Doug? Email questions to ask@maineaudubon.org and visit www.maineaudubon.org to learn more about backyard birding, native plants, and programs and events focusing on Maine wildlife and habitat. Doug leads free bird walks on Thursday mornings, 7 to 9 am, at the Gilsland Farm Audubon Sanctuary in Falmouth.

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