Wednesday, November 13, 2013

Fall 2013 banding season

(Cross-posted at the RRBO web site)

Our 22nd fall banding season took place on 29 days from 15 August to 5 November. An average of 15 nets (12 meter equivalent*) were open an average of 4.6 hours per day. This is the fewest number of days we have been open in a fall season, although our modified hours were intentional -- we wanted to concentrate on maximizing the data we obtain on the fall diets of migrant birds.

Unfortunately, we also lost a 10-day period while we tried to live trap an abandoned cat that had found its way into our banding area. With the safety of birds coming first, we cannot have our nets open when we know there is a predator in the area. We brought this cat to the local shelter, where they felt it was possible it could be put up for adoption. Sadly, people dump unwanted pets here fairly regularly. This is tragic, as is the toll on wildlife taken by owned cats that are let outdoors. I've said it before, but it bears repeating: please keep your cats indoors!

Unlike some years, we did not lose much time to bad weather. I hesitate to complain, but the weather was almost too nice on banding days! The best banding conditions usually occur on calm, overcast days, often before an approaching weather front. This season, over 80% of the banding days were clear or mostly sunny.

Fall banding numbers often also have a lot to do with weather in the preceding seasons. Unlike the ridiculously wet 2011 spring and summer seasons, and the equally parched months of 2012, fall banding was preceded by a spring and summer of relatively normal temperatures and precipitation. April was cool and wet, while May was overall quite warm except for a late frost in mid-month. Average monthly temperatures for June-October were close to the recorded averages for the period 1981-2010. Precipitation for June-October was also close to average, except for August. That month, the rainfall total was nearly three inches above average, but nearly 2.5 inches of that fell on one day, August 12.

Last year's drought caused a serious lack of fruit on shrubs and trees during fall 2012. Nature often makes up for lost productivity, and did so this year. The fruit crop on most plants was abundant if not phenomenal. As noted in my last blog post, the wild grape crop was the heaviest I have seen in over 25 years. Anybody who has an apple tree in their yard can attest that after last year's near complete crop failure, apples were so plentiful that trees broke under their weight. The same was true for their very close relatives crabapples and hawthorns.

The primary non-native fruiting species here are buckthorns and bush honeysuckles. They all seemed to flower and bloom a little later than usual this year, perhaps impacted by the May frost. However, they had large crops.

I noted only two types of fruiting plants that seemed to have below-normal crops. Black cherries, which were one of the few trees that fruited well last year, took a break this year with virtually no crop. Eastern redcedars also seemed to set less fruit than usual.

As might be expected with a modified banding season, we ended up banding a modest 550 new birds and handling 87 recaptures of 58 species. This includes two species released unbanded, House Sparrow and Ruby-throated Hummingbird. A total of 741 birds were netted (which includes birds released unbanded). Our capture rate was 39.4 birds per 100 net-hours. Here is how this fall compared with the 21 previous autumn seasons:

Fall 2013 Previous
fall mean
Days open 28 50
New birds 550 1177
Total birds 741 1502
Capture rate 39.4 48.0
Species 58 69

The top ten bird species banded this fall (new captures only) were:
  1. American Robin -- 118 (low; previous mean 189.7)
  2. White-throated Sparrow --49
  3. Common Grackle -- 35 (new high; previous mean 8.8)
  4. Song Sparrow -- 33 (new record low; previous mean 55.3)
  5. Gray Catbird -- 32 (same as last year, which was record low)
  6. Yellow-rumped Warbler -- 28
  7. Hermit Thrush -- 21
  8. Cedar Waxwing --19
  9. Nashville Warbler -- 16
  10. Ruby-crowned Kinglet -- 15
Numbers and Trends
The high number of grackles is just a hit or miss event. We get very large flocks near our banding site; flocks of over 500 blackbirds, of which most are grackles, is not uncommon in October. They occasionally get flushed into the banding area, but often do not "stick" in the nets.

Banding hummingbirds requires special equipment and a permit amendment, so we release them unbanded. If we didn't, they would have come in at #2 on the list with 40 captured. Some may be repeats of the same bird, but there are often 3 or 4 in the nets at the same time throughout the season, so this is close to an accurate number. They are most often caught in nets adjacent to two plant species at which they nectar: Spotted Jewelweed, a native wildflower; and Glossy Buckthorn, a non-native shrub. The latter has small blooms from early spring through fall and I frequently see hummingbirds using these flowers.

This is the first year we have missed banding any Gray-cheeked Thrushes or Philadelphia Vireos. This may be due to the timing of our gap in banding. This is the third year in a row we did not band any Wood Thrushes. Some years ago, Wood Thrushes were common nesting species here. This is a species that is declining over much of its range, and their absence here may reflect those diminishing numbers.

Both Swainson's Thrushes and Gray Catbirds continued a long-term decline in our nets that I have written about previously. Scrolling down on this page will present graphs on these two species, plus Hermit Thrush; the trend remains the same.

Last year I noted declines in our capture rate* over the last decade. For the first 13-15 years of banding, things moved up and down, but usually remained over 40 birds per 100 net-hours. The average for the years 1992-2004 was 51.6. Since 2005, there has been a pronounced drop. In fact, the drop was quite steep from 2005 to 2008, and since then it has more or less fluctuated in the 30-40 range.

Click to enlarge.

Two important things happened around 2005 that may help explain this: first, the bike path that runs through campus -- wrapping around 3 sides of the banding area -- opened. It gets a great deal of traffic. Second, we began experiencing canopy loss due to falling ash trees killed by the Emerald Ash Borer. This dramatically changed the character of the forested area at UM-Dearborn. Not only did it result in a different mix of trees and shrubs, but probably created a more open and inviting habitat for our increasing deer herd, which alter ecosystems themselves.

So many changes have taken place around our banding site over the years, including the construction of several nearby buildings, and a large, busy parking lot adjacent to the net lanes. Increased development, habitat changes at the site and landscape level, higher numbers of mammalian predators, weather events... it's not possible to tell what may be responsible for our declining capture rate. No doubt it is a combination of things, and we will be pondering the future direction of the banding program in the months to come.

We have only banded 6 Golden-winged Warblers in the past 21 fall seasons, so this bird on September 10 was a treat, and our first since 2005.

The past ten years of so, Northern Waterthrushes seem to be a little scarce, and some years we do not band any. Even just the four we banded this fall was better than we've done since 2006.

An interesting Orange-crowned Warbler was banded on October 14. It had large, distinct dusky centers to its undertail coverts. This is a feature more characteristic of the subspecies that is resident in California, and I've never seen it on any of the birds I've banded here in migration. Bill measurement can be helpful in distinguishing subspecies, and while this one was a little large, it was within the high end of the range of the subspecies expected to pass through Michigan.

A Sharp-shinned Hawk banded in mid-September.

Twenty-three individuals of 9 species of passage migrants (those which do not normally nest or winter in this area) were recaptured. Sixty-five percent of them maintained or gained mass. Half of the birds that lost mass were sparrows. This is fairly typical of this site; insectivores and frugivores tend to gain weight, while seed-eaters tend to lose weight, or gain just small amounts.

We also recaptured 13 birds banded in previous years. The oldest was a female Northern Cardinal first captured in October 2001, making it over 12 years old. Another old bird was a female American Robin first banded as an adult in 2008. She is at least 6 years old. You can view more longevity records here.

We obtained another 318 seed samples from 11 species of birds. This included two new "contributors": a Brown Thrasher (which had eaten pokeweed and grape) and a Willow/Alder Flycatcher (which ate honeysuckle). This brings our total sample size to more than 1,500. Over half are from American Robins, and other large percentages from Gray Catbird, Cedar Waxwing, and Hermit and Swainson's Thrushes.

Credits, kudos
Finally, I’d like to thank Dana Wloch, this year's assistant, and her sponsor, the Michigan Audubon Society. This is the second year in a row MAS has supported Dana's work helping with banding, completing many more species accounts on our seed identification website, and her continued work with our fall dietary study cleaning, sorting, identifying, measuring, and cataloging fruits and seeds. This banding season would not have happened without MAS and Dana, and the on-going work of RRBO could not continue without the support of many donors.


*In order to compare different locations or years that may operate the same number of hours but with more or fewer nets, capture rate is calculated by "net-hours." One net hour is one 12-meter net open one hour, or two 6-meter nets open one hour, etc. This rate is often expressed per 100 net-hours for more manageable numbers.

Weather statistics from the National Weather Service.

Friday, September 27, 2013

Update on fall banding and fruit research

We are a little more than halfway through our modified fall banding. This year, we are concentrating on obtaining as much data as possible on the diet of fall fruit-eating birds. Many bird species switch from a summer diet made up primarily of insects to a fall diet heavy in fruit. This abundant, easy-to-eat food source is particularly important to migratory birds.

After our research showed that migratory thrushes gain weight during stopover at our campus study site, the next step was to pinpoint what resources these birds were using while they were here. Fortunately, there is a reliable and low-tech way to find out: identify the seeds in their poop. (You can find more details by following the links above.) We began collecting samples from thrushes in 2007, and from all birds in 2009. As of the end of last year, we have collected samples from 1,208 birds of 16 species. That's nearly 8,000 individual seeds, of which fewer than a dozen have gone unidentified (see the post on our seed website for more information on how we identify seeds).

Although these seem like big numbers, we need to make sure we have large enough samples sizes from individual bird species during certain time periods to make sure we can do proper statistical analyses. This way, we hope to answer a number of questions, especially whether or not particular species prefers certain fruits and if some fruits help birds gain more weight than other fruits.

This fall, to maximize number of samples we have modified our usual banding routine. When we have done comprehensive migration monitoring, we begin banding very early in the morning, which is when we tend to catch the most birds. Typically, birds captured the first hour or so have not had time to eat much, so we did not obtain many samples from them. This year, we are starting later in the morning and staying open later in the day, providing more overlap with bird foraging. We'll also aim to spend more hours during peak migration/fruiting periods -- late September to mid-October. Overall, this means we will probably band fewer birds, but get more samples.

So far over the 16 days we have banded this fall, roughly a third of all birds have contributed a sample. If we only consider those species most likely to eat fruit -- the primary species are American Robin, Gray Catbird, Cedar Waxwing, and the thrushes, but there are others that eat fruit less often -- the percentage jumps to over 65%. We have collected over 500 individual seeds.

Fruit crops fluctuate from year to year. Last year, the very early spring warm weather and the summer-long severe drought devastated fruit crops.  This year much more normal rainfall and temperatures has resulted in bumper crops of fruit. Some are especially impressive: branches are sagging under the weight of crabapples (both wild and ornamental) and the wild grape crop is nothing short of phenomenal, the largest I have seen in over 25 years.

Not a vineyard! Wild grape crop.
Many factors go into fruit choice in birds: fat, sugar, protein, and micro-nutrient content; size and color; pulp-to-seed ratio; and abundance are just a few. Not surprisingly, the dominant seed in our samples this fall so far is grape, present in 65% of samples. As the crop is depleted and other fruits ripen, the proportion will decline, but no doubt it will be higher than any other year so far. In past years the percentage of grapes has ranged from 5 to 19%.

Grape seeds provided by an American Robin.
This winter we will be doing our first statistical analyses of our samples to see what our data looks like. Stay tuned!

Monday, August 5, 2013

Summer banding 2013

RRBO has done very little summer banding over the years, as we have not had any research projects that require banding during the breeding season for quite some time. This summer, however, our catbird project had us out in the field catching catbirds...and of course we banded whatever else we caught while doing so.

First, we successfully captured enough catbirds to carry all 26 of the geolocators obtained through Dr. Bowlin's grant. On campus, we did targeted netting in a location near Fairlane Lake by setting up a few nets in the midst of the territories of several pairs of catbirds. I also set up our usual fall banding area over a month earlier than usual and the bulk of the catbirds were banded there. In total, at UM-Dearborn we banded 21 catbirds: 7 adult males, 5 adult females, and 9 hatching-year birds. We also captured 5 catbirds (2 adult males, 2 adult females, and 1 hatching-year bird) at a remote site off-campus in Washtenaw County.

Aside from catbirds, we banded 72 other birds of 16 species. The highlight was two hatching-year Orchard Orioles caught in the same net on July 24. This doubles the number of Orchard Orioles banded on campus since 1992; the other two birds were adults caught in the spring. This is an uncommon but annual species here. This year, they seemed more numerous than usual, and apparently nested on campus or close by.

One of the young Orchard Orioles banded this summer.
An adult female American Redstart banded on July 17 was a surprise. There was no physical evidence that she had nested, but it was only our second July record.

We tend not to band many Yellow Warblers in the fall (our 21-year average is 3) because they start to move south quite early in the season. A total of 5 for our modest summer banding was a nice number.

My impression is that House Wrens are having a good year, and we banded a dozen. This is just under our fall seasonal average. We'll see how the fall numbers look.

Our fall banding season begins in mid-August. We will be concentrating on maximizing the data we obtain on the fall diets of migrant birds. We will be banding fewer but longer days, and focus on times of peak bird movement and wild fruit set. After last year's drought-induced fruit crop failure, most fruiting plants are loaded this year. Because we had prolonged cool weather this spring, ripening is a little late, but it should be a very interesting season.

Wednesday, July 24, 2013

Update on catbird research

In 2011, RRBO embarked on a collaborative research project with Dr. Melissa Bowlin, a member of the UM-Dearborn Natural Sciences faculty. Dr. Bowlin had a number of geolocator devices left over from a previous project. Geolocators are tiny devices that measure light levels. This data can be used to calculate latitude and longitude when compared with sunrise and sunset times and light levels at noon in different geographic locations. They can be placed on a bird, and if the bird can be recaptured the following year, the data can be downloaded and migration routes, pace, and destination can be determined. You can read a full explanation of how geolocators work and the goals of the project on the RRBO web site.

In 2011, we placed 11 geolocators on catbirds. In spring 2012, we resighted 3 birds with devices, and recaptured 2 of them.

We did get data from the 2 retrieved geolocators. As it turns out, the data was not high quality; not only do catbirds spend a fair amount of time in shaded areas, but the light-collecting stem on the devices we used was a little short and we suspect ended up being covered by feathers a good amount of the time. Without a good reading on the light, the data from one was deemed inaccurate. The other bird seems to have wintered in Florida -- which is unexpected as preliminary data from other researchers (based on banding and geolocators) indicates that Midwestern-nesting birds winter in Central America. We put the geolocator on this bird on September 29, 2011, it appears to have left Dearborn on October 12, arrived in Florida on the October 16, left the wintering grounds on March 30, 2012, and arrived back in Dearborn on May 8, 2012. We recaptured it May 17, 2012 (here's the story of its recapture).

In fall 2012, we put 2 more geolocators on birds, but did not see any birds with geolocators in spring 2013, despite a lot of patient observation of the catbirds on site.  Earlier this year, Dr. Bowlin received a grant to purchase 26 new geolocators with longer light-collecting stems better suited for catbird study. You can see the older device below in the top picture, and a newer one with the longer "stem" in the bottom photo. They both weigh the same, 1 gram including the harness.

During my spring bird surveys, I spent time locating territories of catbirds that I thought would be easiest to catch and re-find next year. Two of Dr. Bowlin's students, Kelli Gutmann and Quen Watkins, then staked out these birds to see where they tended to hang out so they could be captured with a minimum of fuss. I also set up our regular fall banding site, and began banding a month earlier than usual.

We have had good success so far this summer. We have put 14 geolocators on resident catbirds. Even more exciting, one of the birds I recaptured was a male with a geolocator from 2011! The batteries on the devices can last for 2 years, so if it is good quality we could conceivably get 2 years of data from it. 

We feel confident we can catch enough catbirds for all of our devices, and look forward to finding out what routes they use on migration; if the routes differ for males and females, or adults and young; where the birds stop during migration and how long they stay at each stopover; and where they spend the winter. Stay tuned for more updates!

Friday, July 19, 2013

Yellow-headed Blackbird in Dearborn

Last week, a local man, Ron Prowse, came in and spoke to a co-worker (I was off campus) regarding an unusual Blue Jay-sized bird he had seen at his bird feeders on June 12. He provided this photo.

Photo by Catherine Prowse. Not to be used without permission.
Based on the picture and the description he provided my co-worker, we conclude that this is a Yellow-headed Blackbird (Xanthocephalus xanthocephalus), a new species for the Dearborn bird list!

Yellow-headed Blackbirds are typically a more western species that nests in the grasslands and marshes of the Great Plains. They have nested regularly in Michigan in small numbers for at least 50 years. The most notable small breeding populations are in the Saginaw Bay area. The closest location they are typically found is at Pt. Mouillee State Game Area in Wayne/Monroe Cos.

Map of eBird sightings in the Lower Peninsula of Michigan
for the year 2013.
If I were expecting to see a Yellow-headed Blackbird in Dearborn (which I was not!), I would presume I'd see it during spring migration. A July date is quite interesting, as it would be at a point in their breeding cycle when young are leaving the nest. This wandering bird could be an adult whose nest failed elsewhere, or a non-breeding adult. The most recent sighting at Pt. Mouillee put in eBird was on July 13.

The observer's location not far from the TPC Golf Course along the Rouge River. This portion of the river is channelized, but there is a small wetland on TPC property adjacent to the channel that does have nesting Red-winged Blackbirds and waterfowl. Perhaps the bird was/is hanging around there. Yellow-headed Blackbirds are very tied to cattail marshes for nesting, so the habitat is probably inadequate for that, but it might be a good place to pass the summer.

View Larger Map

Hats off to the Prowse's for this great observation!

This is the 258th species documented for Dearborn. For an interesting historical perspective on Yellow-headed Blackbirds in the state, see Why are Yellow-headed Blackbirds rare in Michigan? by Richard Brewer.