Bluebirds take advantage of empty nest

Q: I have a couple of bluebird nest boxes that I open up in late autumn so squirrels and mice don't roost in there. A pair of bluebirds usually shows up and sits on top of one box or the other for a while right after they're opened up, and I'm wondering why they do this and where they go after that.

A: Once bluebirds have raised their second brood, they and their offspring head for wide open spaces, often parks and refuges, where they feed to fatten up before migration. Many bluebird monitors report seeing bluebird pairs in late autumn sitting on or inside their boxes, and the theory is that these are birds from elsewhere checking out possible nesting sites for next spring.

Q: Most years we see a lot of great egrets, but this summer and fall as we traveled along the Mississippi River we saw very few. Any idea what was going on?

A: That's a good question, and several of my birding friends also mentioned a lack of great egrets this past summer. I checked with Bob Dunlap, president of the Minnesota Ornithologists' Union, who said that he hadn't heard of a lack of great egrets this year.

Vicki Sherry, a biologist with the Minnesota Valley National Wildlife Refuge in Bloomington, hadn't noticed a dearth of egrets, either. The water level on rivers and lakes was high this last spring and summer, which may have caused egrets to change their usual foraging haunts. "It might be that people just weren't seeing great egrets where they were used to seeing them," Sherry said. My conclusion: It doesn't sound as if we need to worry about the great egret population, as these shoreline feeders had probably shifted to shallower shorelines.

Q: While camping Up North I saw a bird I'd never seen before, but can't find it in any field guide. It's pretty difficult to use a guide to identify a bird if you don't already know a great deal about it. How would you go about identifying a new bird?

A: I agree, if you don't have any idea of what a new-to-you bird is, it can be tough to look it up in a field guide. (My sister used to lament that it's impossible to find how to spell a word in a dictionary if you don't already know how to spell it.) A couple of websites might be helpful: www.allaboutbirds.org/building-skills-the-4-keys-to-bird-iden tification/, and http://merlin.allaboutbirds.org. Merlin is a recently launched free smartphone app from the Cornell Lab of Ornithology that identifies birds from questions you answer or a photo you send.

A: The photos you sent clearly show a snowy owl, a species that breeds near the Arctic Circle, although a few wander into our region each fall and winter. Snowies hunt rodents, are active in the daytime and make a spectacular sight, with their white plumage and dark barring. You can find out more here: www.allaboutbirds.org/guide/Snowy_Owl/.

Q: We've noticed warblers hanging around our neighborhood in the fall, beneath hackberry trees on the boulevard. They were in the street and on the sidewalk, and we wonder what they were finding to eat on those hard surfaces.

A: In the photo you sent yellow-rumped warblers were feeding on an asphalt surface, not uncommon behavior for this species. The last warblers to depart in the fall, hardy yellow-rumps consume many kinds of fruit in autumn, and also visit feeders for seeds and suet. They're known to consume the fruits of dogwood, viburnum, honeysuckle, poison ivy, juniper and spikenard, so I see no reason why they wouldn't also eat hackberry berries. Either that, or they're finding late insects and ants underneath the trees on your boulevard. This species is cold-tolerant and willing to try new foods, both factors that help explain why it's our most abundant warbler.

Q: On two occasions we've found the hind section of a rabbit in our yard and wonder what animal is doing this — coyote or fox or owl?

A: It sounds like the work of a great-horned owl to me. Gail Buhl at the Raptor Center confirmed that while it could have been the work of any of the creatures you cited, the most likely is a great-horned owl.

A: Excellent tip. Few of us see flying squirrels, but if we have big trees in our backyards, they're probably out there.

Q: We always leave the fruit on our cherry trees for birds and squirrels, but this past fall they left the cherries alone. Since we had the usual number of birds and squirrels around, we're wondering if Asian beetles sucked the juice out of the cherries, making them inedible.

A: Good for you, for providing such a treat for the local wildlife, and it's a mystery to me why they left this year's crop alone. The University of Minnesota Extension Service is a great resource for answering such questions. You can check their frequently asked questions section or send in your own query via e-mail: https://extension.umn.edu/yard-and-garden/contacts-yard-and-garden.

Note to readers: A reader earlier wrote about a summer storm destroying an eagle nest she'd watched for 30 years at her lake cabin. She recently happily wrote that a pair of eagles were building a nest very near the old site.