Monday, October 22, 2012

Our online seed guide

As regular followers know, RRBO's primary research focus is the ecology of fall migrant birds in urban areas, and one of our main project is examining the fall diet of birds at our urban site.

To do this, we collect fecal samples from the birds that we band, and identify and catalog all the seeds we find. We initially compiled a book of photos of seeds from plants known to occur in the area, as well as a large reference series of seeds collected on campus and nearby.  This has enabled us to identify all but 9 out of nearly 6,500 seeds we have collected in fecal samples from 2007 through 2011.

Although our big binder of seeds and photos was handy, we found we also wanted to have other reference material in it. We also found there was a lot of interest in this project from other researchers as well as land managers and homeowners interested in what birds are eating. We conceived an online reference guide that would include all this information in the form of species accounts.


Thanks to support from the Jimmy F. New Foundation and the Michigan Audubon Society, our web site is coming together. You can take a look at the first set of species accounts: Fruit Seeds of Southern Michigan.

The guide provides accounts of plants that produce fleshy, bird-dispersed fruits, with special emphasis on the identification of seeds. It will focus on fall- and summer-fruiting plant species found in southern Michigan, but since many of these species are widespread in North America, it will be useful for a broader region. Both native and non-native species are covered.

The financial support has provided a stipend for UM-Dearborn graduate Dana Wloch to work on the site. As a student, Dana worked for several years collecting and compiling seeds from our banded birds under two independent research projects. As the "Number 2 of Number 2" she is uniquely qualified for this task, and I'm grateful for her help and work on the web site, as well as sorting through, identifying, and compiling all the seeds pooped out by every species except the Catharus thrushes for the fourth year in a row.


Take a look at our site. It's a work in progress, so there will be many more species added, revisions to the existing accounts, and the bibliography and resource pages will be completed.

Wednesday, October 10, 2012

Banding update

We are well on our way to banding the fewest birds in any fall season in 20 years! The fewest new birds we have banded prior to this year was 739 in 1996. Our "slowest" year was actually 2008, when our capture rate (birds banded as a function of the number of nets we used and the number of hours we had them open) was 33.4 birds per 100 net hours. You can see our current numbers in the right sidebar. I'm pretty sure there is not enough time left in the season for this year not to come in dead last in both categories.

While a lack of birds is disappointing (and kind of alarming), these low numbers are providing valuable data.The weather this growing season is mostly responsible, in particular the drought.  In a previous post, I noted the low numbers of young birds we were banding. This has continued to be the case. American Robins in particular have exemplified the kind of season we are having.

The average number of robins we band in fall is 188, with 300 or so not being uncommon. Prior to today, we had banded only 15!! Today we had 17 more, bringing our total to 32, a remarkably low number.

Based on our 1992-2011 fall data, we can expect around 76% of the robins to be hatching-year birds. This year it is only 23%. This is an indication that robins failed to fledge a "typical" number of young. Since many of the robins we are catching now are migrants likely to have nested elsewhere, this suggests that nesting failure was not just a local problem. And indeed, the drought covered a very large part of the continent.

One interesting aspect is that nearly half young birds I have captured recently still had some spotting on their breasts; this is the plumage they have when leaving the nest. Typically, only about 3% of hatching-year birds have spots this late in the season, having already mostly completed their fall molt. Similarly, 61% of the adult robins are still completing their fall molt. In the past, only about 16% were still molting at this time of year. It looks like, then, that many robins nested late this year -- probably after losing an earlier brood.  It's possible that the skewed ratio of young to older birds may even out a bit in the next couple of weeks.

The prolonged and severe drought contributes to low reproductive success by diminishing food supplies, especially for birds like robins that utilize a lot of leaf-litter or soil invertebrates to feed their young. Besides just reducing the number of birds available, the dry weather contributes to our low capture rates by impacting the fruit crop. Our very early spring heat wave also compounded the failure of many types of wild fruit, as I discussed earlier in the season. Fruit is a vital food source for many species of migratory birds, and of course, a main topic of our research.

In short, many of our staple fruiting plants had small crops or did not fruit, or fruited later than usual. I noted that locally, fruit crops were better in areas adjacent to water. Our banding site is not (unlike many banding stations, which are located in some sort of coastal situation). So this year provided interesting insight into the impacts of growing season weather.

In a future post, I'll provide an update on the 2012 fruit crop and what we found birds were eating.