A browntail caterpillar is shown feeding on a plant, but remember any insecticide or insect control you use to combat the browntails can also have an impact on any other species that comes in contact. Maine Forest Service via AP

Quite often, when someone wants to take an action in their yard or landscape, they send a question to us at Maine Audubon asking, “Will this affect our birds?” A question that was new to me recently was one asking if spreading diatomaceous earth may affect birds foraging in the area. The quick answer is that there is essentially no harm, but we should always keep the complete picture in mind and think about any indirect consequences.

Diatomaceous earth (DE) is a non-toxic powder made of fossilized remains of single-celled aquatic organisms called diatoms (hence the name). It has many applications but we’ll focus on its use as an insecticide in gardens here. DE works by dehydrating insects that come in contact with it, especially ground-dwelling pests like slugs, maggots, aphids, and ants. It is worth noting that DE is non-selective and can be fatal to most insects that come in contact with it. Because of this, it should be used sparingly because those insects are an important food source for our birds. If we wipe out all the insects, there will be no food for our next generation of birds.

Browntail moth controls are another good example of when our actions can have unintended and indirect effects on our birds. A common control for browntail caterpillars right now is spraying Bacillus thuringiensis (Bt) on leaves of oaks and apple trees as the caterpillars are emerging. Bt is an organic insecticide that, when ingested, causes caterpillars’ stomach linings to rupture, killing them from the inside out. Given the skin irritation and respiratory issues these non-native caterpillars can cause people, that fate might not sound so horrible. But again, like the Diatomaceous earth, Bt is indiscriminate in which caterpillar species it kills. Any caterpillar that consumes the leaves that have been sprayed with Bt will suffer that same fate.

The takeaway here is that while there are a variety of non-toxic or organic insecticides available on the market, we should still focus on the fact they are insecticides. As we continue to see insect populations decline, on the scale of what has been termed an “insect apocalypse,” we should be aware of the impacts we are having and consider all the consequences carefully before taking any actions.


One of my favorite skills as a birder is being able to identify birds without actually seeing them. Recognizing the songs and calls that birds make is probably one of the most challenging things to learn, because let’s be honest, it is hard. There are a lot of birds, making a lot of noises, and often you can’t see them so it becomes impossible to know who or what is making that noise – until now. Thanks to an update to Cornell’s Merlin Bird ID app, it can now identify any birds that your phone’s microphone can pick up. (Download the Merlin Bird ID by Cornell Lab and choose Sound ID on the start screen.)


This free app is pretty remarkable. Thanks to about 80 volunteers annotating over 70,000 recordings, the app has been trained to identify more than 450 species of birds in North America by their vocalizations. This is a big improvement over past attempts that require the user to specify which noises should be identified. Merlin will simply produce a list of likely species in real time, as the birds are singing.

The one thing every user needs to be aware of is that it isn’t perfect. From Merlin’s own help center, they answer the question: “Is Merlin always right? No. Merlin shows a list of possible birds based on the songs and calls you recorded, and matches that with the birds that are likely in your area.” Users should always confirm what the app is suggesting, by comparing to the included recordings, or preferably, getting a visual confirmation. One common mistake I’m seeing made right now is that a lot of people are reporting Philadelphia vireos, which have a nearly identical song to the much more common red-eyed vireo. These songs are similar enough that Merlin is easily tricked, but birders are unfortunately reporting all of these Merlin-identified Philadelphia vireos to sites like Cornell’s eBird (an online database for bird sightings). This spring, Philadelphia vireos are being reported with more than twice the frequency in Maine than in any past year.

So keep in mind that, when using the app, with great power comes great responsibility. Go download the app. Use it to hear what might be around you. Then track down those suggestions and get a visual confirmation, at least before you submit that sighting to eBird. When I am leading bird walks and people ask “how do you know that bird song?” I joke that as long as I answer with confidence, people will believe me. Beware that Merlin may also give off an overly confident vibe.

Do you have a nature question for Doug? Email questions to [email protected] and visit 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 a.m., at the Gilsland Farm Audubon Sanctuary in Falmouth.

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