Oregon Songbirds: Singing for Their Supper in Evergreen Forests

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[Steven Sobieszczyk] You are listening to episode 16 of the USGS Oregon Science Podcast for Tuesday, March 8, 2011.

In this episode we sit down with USGS wildlife biologist Joan Hagar and discuss her recent study on songbirds in the Pacific Northwest. New research indicates a possible relationship between reductions in the abundance of some species of songbird and reductions in the amount of deciduous trees in evergreen forests. Join us, as we demonstrate how Oregon songbirds sing for their supper in evergreen-dominated forests, only in this month’s episode of the Oregon Science Podcast.

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[Ruth Jacobs] Hello, and welcome to the Oregon Science Podcast. I’m Ruth Jacobs.

You don’t have to look far to find questions about the effects of management and other forms of change on wildlife. Particularly in forests, birds can be good indicators of change because they are so closely tied to the forest structure. That structure is the vertical and horizontal distribution of trees, shrubs, and other plants, and the structure often changes, sometimes dramatically, with disturbance. Today we are talking with Dr. Joan Hagar, who is a research ecologist with the USGS Forest and Rangeland Ecosystem Science Center. A large part of Joan’s research focuses on habitat for birds in the Pacific Northwest, and she’s one of the authors of a recently completed study that looked at the importance to birds of deciduous vegetation in conifer-dominated forests.

Hello Joan. Welcome!

[Joan Hagar] Thank you, Ruth. It’s nice to be here.

[Ruth Jacobs] Joan, there are a wide variety of birds that live in Pacific Northwest forests. Which ones are you studying?

[Joan Hagar] I focus on the diurnal songbirds. Those are the birds that are active during the day—the ones you hear singing in the forest if you go out on a nice May morning. They mostly eat insects, fruits, berries, and seeds.

[Ruth Jacobs] Often people think about old forests with big conifer trees in the Pacific Northwest. Is this what these birds use for habitat?

[Joan Hagar] Conifers are a really important part of habitat in the Pacific Northwest, but there are not very many species of birds that rely solely on conifers. They rely on a wide diversity of other plant species that are out there—non-coniferous plants like deciduous shrubs, deciduous trees, like maple, and even grasses and forbs in the lower layers of vegetation.

[Ruth Jacobs] We have a deciduous part of the forest, and then we have conifers there as well. These are quite different forest types. What influences the kinds of forests that are out there?

[Joan Hagar] Well, disturbance is a really important influence on the forests that are out there and the composition of forests. There can be natural disturbance, like fire and windthrow, that will influence the light and therefore the vegetation, and there can be management disturbances, such as harvest.

[Ruth Jacobs] You’ve been doing science, collecting information in these forests about bird habitat use. Do you actually go to forests and monitor the birds that are there? And if so, how do you do that?

[Joan Hagar] Yes, that’s the best way! The best way is to go out and actually count birds. There’s a method called Point Counts where we go out and stand at a point and record every bird we hear and see. Lots of my colleagues have done these Point Counts, so that there is a vast data set available, which we have taken advantage of in our recent study to analyze many of these data sets at once. And, there’s also the Breeding Bird Survey, which is a national effort to monitor birds that we can use data on population trends.

[Ruth Jacobs] It sounds like you have some results from a recent study where you use some existing data to look at bird presence. What did you find?

[Joan Hagar] We found, for twelve species that we focused on, a deciduous component was very important to their habitat. The numbers of each species that we found at a site were influenced by the amount of deciduous vegetation.

[Ruth Jacobs] You chose twelve species to look at. Why these twelve species?

[Joan Hagar] These were common songbird species. Many of them have shown signs of declining populations over recent decades.

[Ruth Jacobs] It’s an array of species that managers might be interested in because there’s evidence of decline, and they might be interested in how their management practices are influencing these birds. Is that a fair assessment?

[Joan Hagar] Yes. The managers are interested in these birds. Some of them are also near-tropical migrants, which is a category of management concern for many managers and also for managers who are interested in providing for wildlife. Some of these species with declining populations are of concern.

[Ruth Jacobs] Is the issue diet? Nesting? Or is there something else going on there?

[Joan Hagar] Well, many of these birds eat insects, especially during the summer. Insects are an important component of their diet. We know that insects are more abundant, and the insect community is more diverse on deciduous hardwoods than on conifers. So that could be an important aspect.

[Ruth Jacobs] You know Joan, it always seems that managers are trying to balance a variety of considerations. Did you get any information about how much of this deciduous habitat is enough?

[Joan Hagar] Well, it did vary a lot with each species of bird, but anywhere from about 1% to 25% of the overall canopy cover seemed to influence these bird species.

[Ruth Jacobs] But every bird doesn’t need the same habitat, right?

[Joan Hagar] No, each bird has unique habitat requirements, and that’s one of the key things about having deciduous shrubs and hardwoods out there. There are so many species of deciduous plants, and they each offer different resources.

[Ruth Jacobs] How might a manager apply the results of this science?

[Joan Hagar] Well, if managers want to consider habitat for birds in their management plans, our results indicate that even leaving a little bit of deciduous cover for the birds can go a long way towards maintaining bird populations.

[Ruth Jacobs] Sounds like a pretty big topic. Do you have more research planned to get at additional information about bird use of forest habitat?

[Joan Hagar] Yes, we would like to investigate the influence that birds have on insect pests and contrast their influence in plantations that are mostly pure conifer, compared to young forests that have a deciduous component, where there may be more birds because there’s more deciduous vegetation.

[Ruth Jacobs] You talked about “we.” I’m assuming you work with an array of colleagues. Do you want to make any mention of them?

[Joan Hagar] Yes, I work with Matt Betts at Oregon State University. He’s the leader of many of these investigations.

[Ruth Jacobs] Excellent Joan! Well, thank you very much! We look forward to hearing more about your research at some future date.

[Joan Hagar] Thanks, Ruth.

[Ruth Jacobs] To summarize, different species of birds often are closely associated with the trees, shrubs, and other plants found in a forest. New science by Joan and her collaborators lends support to the idea that reductions in the deciduous component of Pacific Northwest forests are associated with declines in several species of songbirds. One option for managers working to reduce such decline is to restore or maintain this forest component, and interestingly, the science suggests that if this is what a manager wants to do, it might not take much to make a difference. Check out our transcripts to links for more information about Joan’s and others research with the USGS. For those who subscribe through iTunes, you can access the transcripts at our website, at http://or.water.usgs.gov/podcasts. If you have any questions or comments about the USGS Oregon Science Podcast, please email us at oregonpocast@usgs.gov.

Thanks for listening.

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