In the winter, the alarm goes off at 6am; in the summer at 5. It’s hard getting up. It kind of sucks. I look around and it’s still dark, and sometimes cold, and I think there’s no way I’m getting up now. Bed is so cozy, blankets so warm… the wind is playing in the trees outside, rain sometimes gracing the earth and showering its inhabitants.
I remember why the alarm went off. Why the roar of the wind now sounds like a purr, enticing and intriguing and pulling me out of bed. I’m up for the birds. Their songs are already floating through the windows and echoing around the street as I pack up and head out, binoculars in hand.
Currently I’m looking for someone specific. I’m looking for a chatty and energetic little bird called a yellow-rumped warbler (Dendroica coronata, Family Parulidae), common throughout Humboldt county this time of year. Officially, I’m gathering warbler data for my senior thesis; unofficially I’m looking at all the other birds, recording bird vocalizations, taking pictures and looking for frogs because why the hell not. But while I’m on the subject, let me give you the lowdown on my project (because it’s pretty awesome, if I do say so myself): “Foraging resource partitioning of 2 subspecies of the yellow-rumped warbler at the Arcata Marsh and Wildlife Sanctuary”.
Wuuuuuuut. Big words. Science words (yay!). Let’s break it down.
Foraging is the act of finding food. All animals forage in some form, whether they dig for bugs, fly around looking for nectar, stalk a wildebeest… if you’re looking for food, you’re foraging. The behaviors exhibited while foraging can vary, depending on the species, the environment, and the food being searched for.
Resources supply things to us. In the case of my project, I am focusing on those resources that are supplying food to my warblers, that is, the trees and shrubs in which they are foraging.
Partitioning can occur when different species divide resources among themselves somehow, to reduce competition for these needed resources.
Now here’s the cool part: the species yellow-rumped warbler contains 4 subspecies (subspecies can be genetically or physically distinct populations of a single species, although the true definition of subspecies isn’t quite that simple). There are two non-migratory subspecies in central America, and two migratory ones here. These migratory populations are the ones that I am interested in, as their ranges often overlap, which gives me the opportunity to observe them in the same spaces. We have the Myrtle warbler (Dendroica coronata coronata) and the Audubon’s warbler (Dendroica coronata auduboni). The easiest way to tell them apart is to look at their throat: Myrtles have white throats, Audubon’s have yellow throats. Otherwise they are practically identical birds, with beautiful black and gray pattering on their backs and striking yellow rump and armpit patches.
A good many years ago, a guy named Robert MacArthur thought that warblers were pretty cool too. He was one of the first biologists to look into resource partitioning of songbirds, and his studies revealed some neat things. He found that multiple species of warblers foraged in different parts of trees to avoid competing with each other for food resources. Certain warblers were more likely to forage at the very tops of trees, while others would forage lower. Some preferred the outer branches, and some stayed nearer to the trunk.
Nature! You are so cool! These birds have shown that they know how to share their space while they are feeding in the same habitat, thereby maximizing the food that they can acquire without engaging in conflicts with other birds. Now, this does not mean that all birds do this, or that this is a universal rule among animals sharing space; in fact, many animals just chase competitors away from their resources. We can’t know how certain species interact with each other until we take a critical look at them. Which is why I am excited for my project, because I am doing just that! My goal is to see if subspecies of warblers divide themselves among shared resources, as many warblers have been shown to do. When I go out on my birding trips and I see yellow-rumped warblers, I record their position on the tree, and the behavior they are showing as well (as different birds will forage in different ways). I hope to be done with data collection by the end of the month, and once the stats are run, I’ll let you know the findings.
Maybe you weren’t expecting a wildlife biology lesson today, but in any case, I hoped you learned. And I hope you come back to learn more! Because the wonderful world of wildlife is always displaying new and beautiful things, evolving to a changing world, and giving us the opportunity to share fascination with each other. My goal here is to entertain and educate, and take you on this journey with me through the natural world around us. There is so much to see and discover! And I hope you can appreciate that I want to share this passion with you, friends.
Now go outside and look at a bird!