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Q: Why are two sets of eastern bluebirds taking care of the same box? They have been nesting for about two weeks.

Ornithologists don’t know exactly why this happens, but they can offer educated guesses. This unusual circumstance may be a case of cooperative breeding where two breeding pairs are sharing the same nesting space. Cooperative breeding can be a sign of limited nest availability; the birds are making the most of a limited resource. Or, alternatively, these two pairs might be competing for the same nesting site.

South of the Missouri River, bluebirds are year-round residents. In spring, this resident population is joined by migrants coming from the south. All are competing for available nesting cavities. Bluebirds tend to be early and persistent nesters. The year-round residents and early arrivals tend to prevail against other competitors.

Eastern bluebirds begin arriving at their breeding locations in our state in March and April and migrate south in October and November. They are cavity nesters, laying eggs in a hollowed-out nook in a tree created by some other animal, such as a woodpecker. Competition for such sites has led people to construct nest boxes that fit this species’ requirements. There are usually two to seven eggs in a clutch, and two broods per season.

Recent reports indicate the bluebird population has increased significantly. This may be due to the periodical cicadas we saw in 2024. For this reason, conservationists are encouraging the public to consider mounting additional bluebird nesting boxes.

You can read more about competition for nesting at short.mdc.mo.gov/4j9.

Q: I am seeing a buck with unusual antlers. They are always covered in felt, and I don’t think he has ever shed them. He keeps company with two other bucks of smaller stature. Could the odd antlers have been caused by an injury?

Yes, possibly. Bucks typically shed antler velvet in late August to early September. When a buck’s velvet remains attached to his antlers beyond the normal time, it’s often caused by a birth defect known as “cryptorchidism,” also known as undescended testes. This occurs when the normal production of testosterone is diminished, and the antler cycle of hardening, velvet shedding, and antler casting is disrupted. These same results can also occur in normal bucks that later suffer testicular injuries. For more information on this topic, visit short.mdc.mo.gov/4jV.

Q: What species of bird is this?

This is likely an adult female Baltimore oriole (Icterus galbula). These birds are usually seen foraging high in leafy, deciduous trees in open woodlands, but not in deep forests. Forest edges, riverbanks, and small groves attract these birds, which is why they often visit parks and backyards. These birds build socklike hanging nests, woven from slender fibers and anchored to the forks of slim tree branches.

If this bird was a female orchard oriole (Icterus spurius), it likely would have a greenish tint to its plumage and a more distinctively down-curved beak. Female Baltimore orioles, in contrast, are more yellow-orange with bold white wing bars.

Orioles are omnivores that search for caterpillars, beetles, fruit, and flower nectar. They will come to nectar feeders and will consume the pulp of oranges cut in half. During winter — when orioles are in Central America — they drink mostly nectar from flowers. For more information about orioles, visit short.mdc.mo.gov/4jy.