Bullock’s Oriole (Photo by Don Reimer)
Bullock’s Oriole (Photo by Don Reimer)
Typically, we Mainers anticipate neotropical arrivals of Baltimore Orioles in the month of May. In some instances a few tardy individuals (often inexperienced hatch-year birds) linger around bird feeders into fall and early winter. The eventual fate of remaining winter stragglers is always uncertain, given the harsh weather conditions. Take notice that we are speaking specifically of Baltimore Orioles here. 

Following a lengthy stretch of strong winds and pelting rain on November 14, Melinda Sortwell noticed an orange-yellow bird amid the assortment of bird feeders outside her Camden residence. About robin-sized, it was certainly some type of oriole probing the tray of dried mealworms and seeds she had provided. Melinda studied the plumage detail as she pondered its identity. Was this a Baltimore Oriole or could it be a different species of oriole?

The bird’s black lores, black chin and a rather prominent white wing patch did not match any plumage phase of Baltimore Oriole. Melinda concluded this was likely a first-year male Bullock’s Oriole, a western counterpart to the Baltimore Oriole. The Bullock’s ranges from the U.S. West Coast to the Great Plains region and spends its winters in Mexico and Central America.

News of the oriole quickly spread on the Maine Birds Googlegroup website and soon a cavalcade of questing birders appeared at the Camden property, where they were heartily welcomed to view the bird. Expectant birders waited patiently near the feeders for a glimpse. For some days, the bird followed a fairly predictable daily schedule at the feeders; otherwise, it cruised the hardwood treetops of the surrounding neighborhood. Through mid-December nearly 70 visiting birders, some from outside Maine, trekked to Camden to witness the sighting. So what was the big deal about this particular winter oriole, you might rightly ask?

From 1983 until 1995 the Baltimore and Bullock’s orioles were combined as a single species, the Northern Oriole. This was due to hybridization between the two species in the western Great Plains, where their summer ranges overlapped. When genetic research determined that the two species were not that closely related, they were “resplit” into two separate species by the American Ornithological Union in 1995.

The Bullock’s is named for English naturalist William Bullock, who studied the species in Mexico. There were only two confirmed Bullock’s sightings in Maine since 1961. Although much of their breeding biology is similar, the two oriole species differ in certain ways. With help from her mate, the female Bullock’s weaves a gourd-shaped, pendulous nest in large deciduous trees in fairly open habitats. One partner often works on the inside construction while its mate fashions the outside, adding fibers such as hair, twine and bits of wool to the nest walls.

Oriole diets consist mainly of insects, fruit and nectar.  Bullock’s Orioles use a feeding method called “gaping” to extract juice from fruit. Thrusting the closed bill through the skin and into the flesh of fruit, they pry the bill open once inside and lick up the pooling juices with their brushy tongues. The Camden bird was observed to employ this very technique while dining on grapes at the feeder. Occasionally the birds also use this technique on tough-skinned caterpillars, which are skinned by repeatedly striking them against a stout branch.

Eating live honeybees requires another specialized technique, as the bird detaches and drops the stinger. Bullock’s are one of the few birds that will puncture and eject Brown-headed Cowbird eggs placed in their nest. Although this process occasionally damages their own eggs, the behavior apparently pays long-term biological dividends. 

Postscript: Despite plummeting sub-freezing temperatures on December 9, the young oriole fed actively throughout the day. He will need those nourishing calories from now on.