Every year I have a pair of great crested flycatchers that construct a nest in a nest box I put up for them in my yard. They build a nest and then leave until the next summer when I see them again. They have done this for four years, and I was hoping you might know why. Thanks.

– Tucker Frank, Farmington (14 years old)

Putting up bird houses is a great way to be able to watch and study birds. It is always a thrill to see birds investigating a box you’ve put up, and even better when nesting material is brought in. But what a letdown when the nests are abandoned. I can imagine Tucker’s four years of watching (if you’re 14, four years is a long time) has been especially deflating. It is hard to always know the exact cause, but typically, abandonment is caused by some disturbance, so let’s think about what it could be . . .

For any readers not familiar with great crested flycatchers, these migrants will be returning to Maine in May and are more often heard than seen, giving their loud raspy calls (often likened to the sound of a squeezed dog toy: “wheeep”) from the tops of trees. Unlike their more familiar cousin, the eastern phoebe, who often builds cup nests on porch overhangs, this large flycatcher is a secondary cavity nester, cavities made by someone else – like a woodpecker or like Tucker – who has provided a place for them by putting up a bird house.

It is not uncommon for great crested flycatchers to return to the same box in consecutive years, following the typical “if it ain’t broke, don’t fix it” pattern. It is a bit surprising that they haven’t been successful (so something is ‘broke’) but still come back each year to try. They like the box, or they wouldn’t keep trying. First off, make sure the box has adequate drainage; maybe drill an extra hole or two in the bottom corners to allow any water to drain.

A squirrel leaps through the grass with an acorn in its mouth at Deering Oaks in Portland. A squirrel’s predation is one possible reason a great crested flycatcher might not maintain its nest for a full season. Ben McCanna/Staff Photographer

The next thing that I’d suspect is predators. Are there cats around? Outdoors cats are killing billions of birds each year in the U.S. alone, so it would be good to chat with neighbors about keeping their pets indoors, especially during the nesting season (but all year, please). Then we can think about natural predators or competitors, like squirrels. Gray squirrels and flying squirrels may also be eyeing those boxes, either for their own use or for the freshly laid eggs to eat. If those squirrels have learned this is a reliable place for food each spring, you could try moving the box to a different place, or mounting it on a pole that would be harder for the squirrels to reach.

There are some interesting studies that have looked at great crested flycatcher nest predation based on the presence of snake skins inside the nest boxes. Among the grass, twigs, hair, feathers, rope, etc., that these flycatchers use to make their nests, they are well known for using pieces of shed snake skins in the nests as well. Researchers found that adding snake skin to the nest boxes lowered the number of squirrels trying to claim the boxes in the spring, and reduced the predation by small mammals during nesting. I’m not recommending you add snake skins to the nest boxes, but perhaps think about keeping your yard snake-friendly. I know it might be quite a reach since many people have ophidiophobia, but hopefully this example shows how wildlife and habitat are all interconnected, and how important it is to nurture a complete and healthy ecosystem.

DO CARDINALS MATE FOR LIFE?

For the past 30 years we have lived in an old cape on the Pemaquid peninsula surrounded by fields, woods and wetlands. Over this time, there have been a pair of cardinals nesting nearby and visiting our feeders throughout all four seasons; only one pair and their fledglings without fail each year … We can’t possibly be seeing the same pair all this time. How long do cardinals live, and do they mate for life? Could we be seeing successive generations returning to their original nesting area?

– John & Barbara Allan, Pemaquid

Cardinals, with the male at left and female on the right. You might see cardinals every year in your yard, but do not assume it’s the same pair … or that the pair itself is even still together. Apparently, cardinals have a “divorce rate” of about 20%. Associated Press photos

It is a very common misunderstanding to think that the birds returning to your yard each year, often nesting in the same spot, are the same individuals. From what we know about different species’ longevity and family dynamics, it is almost impossible for them to be the same in many of these long-term cases, as John and Barbara suspect. We can use their excellent northern cardinal example to explain.

The oldest known northern cardinal, according to the Bird Banding Laboratory, was at least 15 years and 9 months old, a female that was first caught and banded in Pennsylvania in March 1956. The best way to know the age of individual birds is for a licensed bird bander to catch (then measure, weigh, etc.) and place a band on the bird’s leg. Each bird gets a lightweight aluminum band with a unique set of numbers, which you can think of as the bird’s Social Security number. Then if the bird is ever caught again, its information can be referenced to learn things like how old it is, where it has been, and much more. That cardinal banded in Pennsylvania was already an adult when it was first caught, which is why I said it was “at least 15 years old.” So while there may well be older cardinals out there, 15 years is probably a long life for the average cardinal.

Knowing that the cardinals are being replaced on this Pemaquid peninsula, we can think about their pair bonds. While there are some fun examples of birds that “mate for life,” my preferred explanation is that they’ll mate for life as long as it is mutually beneficial. We often see paired cardinals sticking together, even in the non-breeding season, but studies have shown this species has around 20% “divorce rates” through the year. Even while being “socially monogamous,” cardinals are known for being polygynous (having many female partners), as a male will mate with multiple females within his territory. Females are also documented to have “extra-pair fertilizations” (many males contributing to a nest) which is probably a good way to not put all your eggs in one basket.

We should also note, as John and Barbara assumed, that subsequent generations of a family will often stay in the same area. So the offspring of the successful cardinals from 30 years ago likely stayed within the area that they were born. Then, as their parent’s territory became vacant, they moved in. So even though it may not be the same “Carlton the Cardinal” that has been in your backyard for 30 years, it is fun to know that it might be Carlton the Cardinal Junior or perhaps, more likely, Carlton IV.

ABOUT THOSE ARBORISTS

In my March 21 column, I made what was truly meant to be a lighthearted comment about arborists. Maine Audubon works closely and productively with many arborists and knows them to be professionals who are careful to balance a love of trees, habitat, and wildlife with a need for safety. Their expertise in evaluating wildlife needs and other concerns in tree removal was not meant to be overshadowed by my lighthearted attempt to expose my own bias as a naturalist. I’m sorry for any misunderstanding and any unintended slight.

Do you have a nature question for Doug? Email questions to [email protected] and visit maineaudubon.org to learn more about virtual and backyard birding, online classes and other programs about wildlife and habitat.


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