Morse Preserve: June 26th, 2011
By Emma White
In attendance: Daniel Froehlich, Clarice Clark, John White (driver), Emma White.
Rufous Hummingbird 4
Western Wood-Peewee 1
Hutton’s Vireo 1
Red-Breasted Nuthatch 1
Pacific Wren 4
Bewick’s Wren 1
Swainson’s Thrush 2
American Robin 1
Cedar Waxwing 1
Orange-Crowned Warbler 2
Western Tanager 1
Spotted Towhee 5
Song Sparrow 1
Black-Headed Grosbeak 1
Brown-Headed Cowbird 1
June 26th dawned bright and early at the Morse Preserve. We had nice banding weather on the horizon and ten nets set up ready to catch birds.
Although our total for the day was only 30 birds, many of the birds caused excitement among the group. A Cedar Waxwing and a Western Tanager both fell into the nets, and were eagerly looked at by the group. The Western Tanager in particular became more and more interesting as it was looked at closer.
Looking at the bird, Dan was easily able to see a clear indication of a molt limit present on the bird’s wing. He explained how the molt limit in the primary feathers on the bird helped to age the bird as a SY. Another interesting part of the wing on the Western Tanager was the tertials. All three of these feathers are black with white tips. As you can see, the tertial that is on the bottom has more white than the other two. This is because the bird recently molted this bottom feather, causing it to look blacker than the other two feathers, with a less worn white tip. This stage of molting is a great indicator of the age of a bird.
We were all surprised when a Western-Wood Peewee wandered into one of our nets during our morning at Morse. We’d been hearing Willow Flycatchers all morning and expected the bird in front of us to be one of them, not a Peewee, who had been mysteriously quiet all morning. It was a pleasant surprise though, and after it had flown off, we began hearing it occasionally throughout the rest of the morning.
A Brown-Headed Cowbird also made its way into one of our nets. After determining its molt limit, age, sex, etc., a common question among birders was raised: should people around the world be systematically killing Brown-Headed Cowbirds? The topic is a much-debated one among birders, as it’s easy to see both sides of the issues.
Brown-Headed Cowbirds are brood parasites. This means that instead of taking the normal route of raising young, Cowbirds do something different: they find a nest belonging to another bird species (particularly passerines) and then lay there own eggs in said nest. They may kick out the other species’ eggs to make room for their own, or just because of the nature of Brown-Headed Cowbirds’ growth (they grow and hatch faster than a Cowbird’s host species’ young tend to) the presence of Cowbird eggs in another bird’s nest can be deadly for that bird’s young. Also, because of their parasitic ways, Brown-Headed Cowbird females don’t even have brood patches, meaning they’re not even physically able to incubate their young like other non-brood parasitic birds do. They then leave the eggs there to be raised by whichever species of bird the nest originally belonged to.
So why kill them? The problem with the Brown-Headed Cowbird’s reproductive strategy is that in order for the Cowbird’s young to survive, the host species loses many of its young in the process, causing some species’ numbers to be extremely negatively affected. This is true in the case of the Kirtland’s Warbler.
The Kirtland’s Warbler is a warbler native to Michigan, living only in the Jack Pine forests there. Specifically, they can be found in new growth Jack Pine forests where forest fires have caused forests to begin again and re-grow completely. When humans began to stop the forest fires from occurring, the Kirtland’s Warbler’s habitat decreased, leaving them with only a small area of suitable forest to live in. This caused their population to steadily decrease. In addition to habitat problems, the Kirtland’s Warblers were also being parasitized by Brown-Headed Cowbirds, causing their population to decline even more. This led them to near extinction in the middle of the twentieth century.
In an effort to bring this species back to survivable numbers, humans have done two things: started and planned for forest fires in Jack Pine forests in Michigan and killed Brown-Headed Cowbirds. And the species responded. Today, Kirtland’s Warblers are listed as only “Near Threatened” instead of their previous “Near-Extinction” status. The revival strategy has obviously been working.
So, should we be killing Brown-Headed Cowbirds? For PSBO during our MAPS banding sessions, the answer is clear: no. The purpose of the MAPS program is to document what bird species live and reproduce in which areas. By killing Brown-Headed Cowbirds at our banding sites, the data collected wouldn’t be an accurate representation of which birds are in those areas. The larger question, of whether or not Brown-Headed Cowbirds should be killed around North America purposefully every year, is a much harder question to answer. The reduction of Brown-Head Cowbirds around the country is done for a reason. It’s done to help protect other bird species that are being parasitized by Cowbirds. At the same time, Brown-Headed Cowbirds are still living, breathing birds. What is the right path for humans around North America to follow? Do we kill Brown-Headed Cowbirds, or do we let nature run its course? This is a question for you to ponder.
In addition to catching some new birds, like the Brown-Headed Cowbird, we also caught some birds that we had captured previously. Out of these seven birds, though, only one of them had been originally banded prior to this year. That little bird was the female Hutton’s Vireo that we caught. Originally banded on June 20, 2009 as an after hatch year (AHY), we caught her again in both 2010 and 2011. Based on the age criteria given to her from 2009 to 2011, we can estimate that she’s at least four years old. She’s also an exciting catch because she’s had a brood patch every year. This is a positive indication that she may be breeding on site at Morse!
Overall, we had a very successful day at Morse. We weren’t overrun with birds, which allowed discussion on topics such as the Brown-Headed Cowbird dilemma to occur. It was a fun day, and the birds we did catch were interesting and beautiful.