Thursday, June 4, 2015

Northern Parula

This year's Spring migration is all but a memory now, and most species are currently focusing on raising a successful brood. I, however, want to revisit a day during migration for this post. On May 19th I had the chance to visit the famous boardwalk at Magee Marsh along Lake Erie. Sadly, I was a few days late for the Biggest Week in Birding, but Spring migration was still hopping. I saw many warblers and assorted other migrants, but one Northern Parula gave me and a few other birders quite the show. I was fascinated by this Parula and decided to write up a post about the species, so here we go!

The Northern Parula, Setophaga americana, is a small migratory warbler. You might be wondering where in the world the name "Parula" came from. When this species was first classified by Carl Linnaeus in 1758, Linnaeus considered it to be related to the tits of the Old World. The name for this genus was Parus, and that was slightly changed to Parula for the common name of this species. However, the Northern Parula isn't a tit, and is instead a new world warbler. Like other neotropical warblers, the Parula spends half the year in more southerly climes and the other half in more northerly climes to breed. During Spring (April-May in Ohio), this species migrates from parts of Central America and the West Indies to the Eastern United States and Eastern Canada. It then spends the next few months trying to find a mate and raising a new generation before migrating back south to overwinter.

Northern Parula Magee Marsh
Where can you find this species in Ohio? Well, it depends on when you're looking. They can essentially be found anywhere across Ohio during migration, especially in the southern portion of Ohio and along the Lake Erie coast. It's a little harder to find this species during the Summer. They breed in the Allegheny Plateau region of Southern and Eastern Ohio, becoming scarcer the farther North you travel. The Northern Parula breeds in well-established forests here in Ohio. The older forests of Southern Ohio typically hold a good number of individuals. You can always find some in the Hocking Hills region, as well as Adams County. If you're looking for one though, good luck! The Northern Parula is a tree-top gleaner, meaning it feeds on insects that live on the branches in the canopy. Parulas are also roughly the same size as a chickadee. Spotting this tiny bird when it's 80 feet up in the leaves is definitely a frustratingly hard thing to accomplish. To help know when there's a Northern Parula near you, learn their song! It's a fairly easy song to learn, and you will find ten times more individuals this way than you would by just scanning the trees in hope for one. To listen to some examples of their songs, go to this link and look on the bottom right for "Songs and Calls."

Northern Parula Ohio
At Magee Marsh during Spring migration, things are a little different. Tree-top gleaners, such as the Northern Parula, might be only 5 feet off the ground. On top of that, the warblers are so focused on getting enough food to make it across Lake Erie that they essentially ignore all the people around. That means there might be a warbler only an arm's length away and right at eye level. Regardless of how cheesy it sounds, I can only describe Magee Marsh as a magical place, and birders who have made the trip know exactly what I'm talking about. This Northern Parula was no exception, foraging right at eye level only about 5 feet away. In the photo above you can see him checking out a leaf for a possible tasty arthropod morsel.

Northern Parula
And turns out there was indeed a tasty arthropod about! He quickly pulled a tiny green caterpillar off the leaf, which you can see in his beak above. As always, you can click on the photo to get a bigger version. While the Northern Parula eats a wide variety of arthropods, their favorites are caterpillars and spiders.

Northern Parula Eating
Another caterpillar victory!
If you look at a range map, like this one here, you might notice something strange. The Northern Parula nests in southeast Canada and the southeast US, but there's a noticeable gap where they don't breed. This gap separates the species into a northern and a southern breeding population. The gap is probably due to a combination of two main factors that I'll discuss below.

Northern Parula
The Northern Parula loves to make nests out of tree lichen. In the south they use Spanish Moss, which is actually a lichen, while in the north they utilize Usnea sp. lichens, commonly known as the Beard Lichens. Is there abundant tree lichen in the gap? Turns out there isn't, but that wasn't always the case. Lichen is very sensitive to air quality, and if you look at the gap you can see that it matches up nicely with big metropolitan areas where air pollution was, and still is, an issue. The Parula more than likely nested in the gap in the past before industrialization, but the air pollution the cities brought killed off the tree lichen species they would utilize. With the disappearance of appropriate nesting material, the Parulas were simply forced to leave that area; however, there is another factor to consider. Parulas favor complex forests where there is a variety in tree height, plant species, and so on. The area that the gap is in was a victim of deforestation, and as a result there is now a very homogenous forest instead of a complex heterogeneous forest. The homogenous, young forests of the area coupled with the lack of tree lichens is probably the true cause of the gap, not just one or the other. Once again, this is another example of human-caused problems. Hopefully the air quality will get better in the gap over the upcoming decades and the Northern Parula will once again return to the area to nest.

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