Foraging: looking at how the birds survive and evolved

As a program in Tompkins County, we are not only working to better understand the ecology, behavior and phenology of the different Cardinalids in our area, but we also hope to compare the biology of at least the two species we are currently focusing on, and gain insights in their evolution. A project that has arisen during our field season this summer and that could bring us closer to several of these goals is the recording of foraging observations. All birds spend a considerable proportion of each day finding enough food for their survival and, eventually, that of their chicks. This makes their foraging central to their life, relevant to everything else that the birds must find time to do.

Foraging not only reveals what birds spend a lot of their day doing, but it central to seeing how birds fit together in a community. In order to avoid competition, birds will theoretically try to either feed on different things, or find the same things in different places. Thus they will fill in a ‘niche’ and coexist peacefully. What we try to do when we watch Cardinalids forage is see both what the birds do and where they look for food, which will give hints on how this has helped them evolve together and coexist. This is especially interesting with the grosbeak and tanager because both nest near each other, forage in similar places, and eat similar things (for example, I have seen them both eat inchworms). How can the birds live in the same place and eat similar things? We think there are probably differences in their foraging styles and tendencies, which is why keeping track of them in the forest becomes a relevant project.

Basically, making a foraging observation consists of narrating what the bird is doing to a hand-held voice recorder. Because birds spend so much time looking for insects, we can do a foraging observation most anytime we find the bird, unless this distracts us from our main purpose for the moment, such as nest watching. The harder part, once we have the bird, is to not lose track of it. This can be easy if the bird stays within a group of trees, but they tend to take sudden, long, swooping flights in random directions, which usually marks the end of a foraging observation.

As part of the observation, it is important to remember to begin by stating the time, observer and species. The time is important because it gives an idea of what point in the day the observation was made, they may forage differently in the morning compared to the evening. The species may seem like a basic note, but it is very easy to forget. Once, when listening to a recording, I was pretty sure that the male I had been following was a tanager, even though I had forgotten to mention the species name. Later on though, when listening to the other recordings I had made that day, I realized that it had to be a grosbeak, mostly because I had begun the observation one minute after finishing another that had been a grosbeak. That mistake could have seriously skewered my data!

After that, we try to keep track of the different foraging methods, or ‘gleans’ the bird performs to capture prey, such as when he  hovers under a leaf, or he snatches something as he flies over it. As we want an idea of how active the bird is and where he searches for food, we also keep track of each hop the bird makes, as well as an estimate of the distance and angle (a, b, or c, each equivalent to 30 degrees).

More personally, I really enjoy making these observations. It allows me to actively follow a bird within the forest, where I can hopefully identify what it is doing, and gather the information so that I will hopefully better understand why it does it in the future. Following the bird also leads to interesting incidents. One big one, for example, was the discovery of the nest SCTA 5 as the male chased a woodpecker away from it. Listening to the recording is interesting, because I described the attack, mentioned that the male was now perched on a sugar maple, and suddenly say to Hilary and Justin: “Guys, I found his nest.” However, as I was recording the birds activities, I only briefly indicate where the nest is to Justin, who pats my back, and go on saying ‘he just, oh darn it! He just did something as he changed perch. He gleaned from a leaf as he changed perch’.

Another memorable experience while recording a bird happened while I was trying to figure out what a female-like tanager was doing in a territory that had already fledged its chicks. However, I had lost track of it and was desperately looking for her in the canopy. A green bird flew into sight and I eagerly began recording its actions, which seemed quite tanager-like. However, after a hover-glean, I realize that it has an eyeline and no black on the wings and … “forget it, because it was a Red-eyed Vireo that looked a lot like a Scarlet Tanager from … high up … How humiliating”. This is probably the one of the worst misidentifications I have ever done, but it has caused be to carefully examine each tanager’s bill and wings to avoid similar situations.

Listening to my voice as I watch the bird makes me realize that, despite all the changes I have gone through ever since I came to college (and these are substantial) I remain the birder I will always be. One random comment while I was watching a male Rose-breasted Grosbeak hop between perches, “[…] He’s beautiful! And, […]”, reminds me of why I want to study birds: it’s because they are magnificent creatures, and I love looking for them, understanding what they do, and appreciating their beauty.

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