Wednesday, December 28, 2011
Thank you from RRBO!
Monday, November 21, 2011
Julie and I have kept in touch throughout her academic career, and it has always been exciting to see her accomplishments accumulate. She has published a number of papers, and her most recent one -- Avian conservation practices strengthen ecosystem services in California vineyards -- was featured in the New York Times!
I like to think that RRBO had a small part in her success. But I know it is because Julie is a dedicated, creative scientist. Way to go, Julie!
Monday, November 14, 2011
Because we had a number of nets that were damaged by deer, instead of trashing them I moved them all into one area and decided to leave them up a little longer. As we have some warm days in November and December, I hope to catch a few more robins (and maybe even a wintering Hermit Thrush) to see what fruit they continue to eat as winter sets in.
As we identify and compile our seed samples from this fall and add them to our database, expect to see a blog post or two on what we have found our birds to be eating. Plus, a couple of exciting projects are being to come together, and of course our winter bird survey is also fast approaching. Stay tuned.
Tuesday, November 1, 2011
Before I continue, let me issue this statement: I strongly believe in the use and preservation of native plants. I am not "pro-buckthorn." I believe it has many ecological liabilities. One prevailing notion is that buckthorn causes diarrhea in birds and is harmful to them. Based on a peer-reviewed literature search, I cannot find evidence that this is true.
Much of the background information here is from an excellent overview paper by Izhaki (2002). Other research is also cited.
Background: Chemical properties of buckthorns
Many plants have what are known as "secondary compounds," chemicals that play important roles in plant fitness and survival. These compounds or metabolites are generally believed to deter the consumption of unripe fruit, since the seeds in unripe fruit are not yet viable. See Cipollini and Levey (1997) for a discussion of other very interesting hypothetical functions of secondary compounds in ripe fruit.
The relevant secondary compound in buckthorns is emodin, a free-form (aglycone) anthraquinone found in 17 families, 28 genera, and 94 species of plants, including 23 species in the genus Rhamnus*. It can be found in many plant parts, including the leaves and fruit. Emodin has many properties. In regards to fruit, emodin can act as an antimicrobial, inhibiting fruit damage. Levels of emodin in fruit pulp typically decrease as the fruit ripens. As explained above, this may help to protect the seeds from being dispersed before they are mature, or eaten and destroyed by seed predators.
The biological activity of emodin (as well as many other compounds) is different in mammals than in birds. Emodin is well-known as a laxative in humans as well as other mammals. What about birds?
Buckthorn and birds
Wherever it occurs, buckthorn tends to be distributed by birds. There are two commonly held and frequently repeated notions about buckthorn fruit: that it causes diarrhea in birds, and that birds in North America don't "know" not to eat unripe fruit and can become very sick or even die from eating it. (Actually, there is a third notion, that buckthorn fruit is "junk food." That isn't entirely true either, but it a subject of a future post.)
The diarrhea myth, I think, starts with the fact that when people see birds eating fruit, they also see the birds poop a lot. This is, in fact, true of most birds and most types of fruit, especially wet, pulpy fruit and fruit with bulky seeds. Fruit passes quickly through bird guts -- many fruits are composed of mainly water and seeds, and nutrients (especially sugars) that are quickly assimilated. Birds only have so much room in the digestive system and it makes sense for them to process fruit as quickly as possible, including jettisoning the seeds. Birds are also able to consume more fruit if they choose species that have short retention times (Cipollini and Levey 1997). Hence, the appearance of diarrhea. I suppose if you define diarrhea as loose, wet, and frequent defecation, then many fruits give birds "diarrhea." But the implication in public discussions is that the frequent, conspicuous defectations of buckthorn pulp is abnormal or harmful. I've seen similar messes near large stands of Pokeweed (Phytolacca americana) and Red Mulberry (Morus rubra), both native plants, and do not hear similar concern for birds' health.
Studies of secondary compounds in fruits (e.g., Wahaj et al. 1998) have indicated that plants exert "control" over the gut retention time of their seeds in birds through these chemicals; this includes both speeding up and/or slowing down of the passage through the digestive system. This is presumably to influence the number of seeds expelled per defecation, the dispersal distance, and/or reduce or enhance the effects of gut passage on the seed coat. This control is advantageous to the plant if it increases its reproductive success.
Regarding emodin, Tsahar et al. (2003), working with Yellow-vented [White-spectacled] Bulbuls (Pycnonotus xanthopygos), found that emodin increased digestive efficiency in birds, aiding in the processing of dry matter, nitrogen, and other nutrients. They determined that this effect was the result of emodin slowing transit time of food through the gut. This study, then, found that emodin has a costive (constipating) effect, not a laxative one, at least in bulbuls.
In their review, Levey et al. (2007) noted,
Despite the widespread detrimental effect of emodin on fruit consumption by vertebrates, ripe fruits that contain emodin are frequently consumed by a wide variety of seed dispersers... suggesting that the net benefits of fruit consumption somehow outweigh the negative effects of emodin. In particular, the nutritional reward of carbohydrates, lipids, and proteins in fruit pulp can be viewed as more important to consumers than the presence of co-occurring secondary compounds.
Do North American birds unwittingly eat unripe non-native buckthorn fruit, which contain higher concentrations of emodin than ripe fruit? Could they consume enough to harm them?
There are at least 14 native species of Rhamnus and Frangula in North America. Several species are widespread, and have similar fruit characteristics (phenology, size, color) as the non-native species. Given the widespread occurrence of emodin in this family, presumably it also occurs in the fruit of the native species. This indicates that North American birds are not naïve to buckthorn or emodin.
Even if they had no experience with fruits containing emodin, studies have shown that many bird species are sensitive to it and adjust their consumption accordingly. Tsahar et al. (2002) found the highly frugivorous Yellow-vented Bulbul could distinguish among artificial diets containing a range of emodin concentrations similar to what is found in ripe fruits, while House Sparrows could only discern emodin amounts similar to what is found in ripe versus unripe fruits.
Both of those bird species are Old World in origin. One of the only studies to take a long look at R. cathartica and North American birds was a doctoral dissertation by James Sherburne (1972). He found American Robins avoided feeding on fruits of other plants coated with emodin, and that even if starved for 12 hours, would only voluntarily eat a few unripe R. cathartica fruits. The unripe fruit contained between 0.6 to 1 microgram of emodin.
Sherburne went on to force American Robins and Gray Catbirds eat unripe Rhamnus fruit or capsules containing emodin. The birds showed signs of diarrhea after consuming 50 micrograms to 5 mg of emodin. At the lowest concentration showing effect (50 micrograms) and the highest concentration given for the unripe fruit (1 microgram), it would require ingestion of at least 50 unripe fruits to cause diarrhea.
Schafer et al. (1983) tested the toxicity of a wide range of compounds on birds, including emodin. The dose of emodin needed to kill half (LD50) of Red-winged Blackbirds and European Starlings was greater than 100 mg per kg of body mass. Under this scenario, an average-sized 65-gram male blackbird would need to consume at least 6500 unripe fruits of R. cathartica (based on the high estimate of 1 microgram of emodin in an unripe fruit from Sherburne) to reach the "LD50" dose. Little wonder the authors calculated a "hazard index" indicating little or no potential for emodin to cause acute poisoning in these species.
Given the ability of birds to detect emodin, their reluctance to eat unripe fruit (three other studies cited in Izhaki  noted that in North America, "most bird species do not consume the unripe fruits"), and the high levels needed to create a negative response, we can probably infer that wild birds do not consume large enough quantities of unripe fruit to cause diarrhea or serious toxicity.
As for ripe fruit, Sherburne found no emodin in ripe fruits of R. cathartica, although other studies have found it in the ripe fruit of other Rhamnus species not yet established in North America (Tsahar et al. 2002). As it is found in far smaller amounts in ripe fruit, the number of fruits that would need to be consumed to cause harm would be many times greater than the examples listed above. Sherburne reported on 11 species of birds that readily ate ripe R. cathartica fruit, but did not mention any negative effects (in Knight et al. 2007).
In the wild, birds tend to mix their diets, choosing fruits and other foods within short feeding bouts, and this may be an attempt to balance nutrient intake or to avoid ingesting too much of a particular secondary compound (Cipollini and Levey 1997) . Further, the varied dietary inputs may contain their own qualities that could mediate any adverse physiological effects of emodin.
There are many ecological crimes we can pin on buckthorn. It doesn't appear that causing harmful diarrhea is one of them. If anybody has seen any other studies or peer-reviewed publications that do show that eating buckthorn fruit is harmful to birds, please post them in the comments. I am fascinated by this topic and interested in learning of new research.
*Glossy Buckthorn, Frangula alnus, has often been included in the genus Rhamnus as R. frangula. It also contains emodin. When I refer to "buckthorn" here, I am referring to both Common and Glossy Buckthorn in general, unless otherwise noted.
Cipollini, M. L., and D. J. Levey. 1997. Secondary metabolites of fleshy vertebrate-dispersed fruits: adaptive hypotheses and implications for seed dispersal. American Naturalist 150:346-372.
Knight, K. S., J. S. Kurylo, A. G. Endress, and J. R. Stewart. 2007. Ecology and ecosystem impacts of common buckthorn (Rhamnus cathartica): a review. Biol. Invasions 9: 925-937.
Izhaki, I. 2002. Emodin -- a secondary metabolite with multiple ecological functions in higher plants. New Phytologist 155:205-217.
Levey, D. J., J. J. Tewksbury, I. Izhaki, E. Tsahar, and D. C. Haak. 2007. Evolutionary ecology of secondary compounds in ripe fruit: case studies with capsaicin and emodin. Pages 37-58 in A. J. Dennis, E. W. Schupp, R. J. Green, and D. A. Westcott, eds. Seed Dispersal: Theory and its Application in a Changing World. CAB International, Cambridge, MA.
Schafer, E.W. Jr, Bowles, W.A. Jr, and J. Hurlbut. 1983. The acute oral toxicity, repellency, and hazard potential of 998 chemicals to one or more species of wild and domestic birds. Arch. Environ. Contam. Toxicol. 12:355-382.
Sherburne, J. A. 1972. Effects of seasonal changes in the abundance and chemistry of the fleshy fruits of northeastern woody shrubs on patterns of exploitation by frugivorous birds. Ph.D. dissertation, Cornell University, Ithaca, New York.
Tsahar, E., J. Friedman, and I. Izhaki. 2002. Impact of fruit removal and seed predation of a secondary metabolite, emodin, in Rhamnus alaternus fruit pulp. Oikos 99:290–299.
Tsahar, E. 2001. The impact of the secondary metabolite emodin in Rhamnus alaternus fruits on fruit removal and seed predation. M.S. thesis, Tel-Aviv University, Israel.
Tsahar, E., J. Friedman, and I. Izhaki. 2003. Secondary metabolite emodin increases food assimilation efficiency of Yellow-vented bulbuls (Pycnonotus xanthopygos). Auk 120: 411-417.
Wahaj, S. A., D. J. Levey, A. K. Sanders, and M. L. Cipollini. 1998. Control of gut retention time by secondary metabolites in ripe Solanum fruits. Ecology 79:2309-2319.
Monday, October 24, 2011
The number of birds we have banded so far in October represents over 40% of the total for the season. Most have come after mid-month, when American Robin numbers increased, and the first big push of Yellow-rumped Warblers, Hermit Thrushes, and sparrows began. It is heartening to see respectable Hermit Thrush numbers. The number of Swainson's Thrushes banded this fall was our second lowest. We have already hit our average for Hermit Thrushes, and are getting plenty of seed samples from them, which is excellent. We're still below average for White-throats, and they don't seem as numerous this year as usual. We have only banded four White-crowned Sparrows, which is ridiculously low. Our average is 22.
Warblers continue to be banded. In addition to Yellow-rumps, late species such as Common Yellowthroat, Orange-crowned, and Palm still are around, as is Tennessee. Every day we still get a Nashville Warbler or two, and we are far over our fall high of 59 Nashvilles banded. Notable was a Blackpoll Warbler banded on 22 October that tied the late fall date for Dearborn -- but one seen the next day furnished the new late date. An American Redstart was also banded on 22 October, and that was a new late date for that species.
Two species were banded this month that we don't get too often: Eastern Towhee and Yellow-bellied Sapsucker.
|Young male Eastern Towhee.|
|Young female Yellow-bellied Sapsucker.|
Wednesday, October 19, 2011
One of the native fruiting plants that is common on our site is poison-ivy (Toxicodendron radicans). The flowers are rather insignificant and can be overlooked.
Poison-ivy fruits themselves are about half the size of a pea, quite dry, and papery. They contain very little pulp. Each fruit has one to three, odd-looking, globular seeds that are very distinctive.
We find the seeds in samples from only a few species of birds. Most often it's woodpeckers, and we've gotten poison-ivy seeds from Downy and Hairy Woodpeckers, and Yellow-shafted Flickers. The sample below is from one dropping from a flicker.
This week, we got two poison-ivy seeds from a Ruby-crowned Kinglet, the first seed samples of any kind we've had from a kinglet. This particular bird was first banded on 7 October, when it weighed 6.3 grams. We recaptured it several more times. On 12 October, it weighed 6.7 grams, on 16 October it was 7.2 grams, and on 18 October it was 7.4 grams. It doesn't sound like much, but that's a 17.5% increase in the bird's original weight.
Poison-ivy fruit are very high in fats (over 40%) and low in sugars. Not all birds are able to easily or efficiently digest and absorb fats. Differences in digestive physiology, as well as the varied nutritional needs among residents, long-distance, and short-distance migrants has a great influence on fruit choice.
In the special case of poison-ivy, the fats in the fruits are also of a waxy (high melting point) nature, and only a few bird species are able to process plant waxes. The eastern form of Yellow-rumped Warbler, found here, is called "Myrtle Warbler" because of its ability to eat the fruit of wax myrtle (Myrica sp.). Poison-ivy fruits are very similar in composition to myrtle fruit.
You may wonder if the compounds (urushiol) in poison-ivy that cause a skin rash in most people are present in the fruit. I'm not entirely sure; some sources say yes, others indicate they are only present in the sap, and therefore only the stems and leaves. In other plants with urushiol, such as mangoes, the fruit does not contain the poison. I'm not very sensitive to poison-ivy, and I have not had a problem handling the seeds once pooped from a bird.
Update: My friend Steve Hamilton has taken some great photos of a Cedar Waxwing and a Yellow-rumped Warbler at poison-ivy, and a video of a Yellow-rumped Warbler eating poison-ivy in Ohio.
Tuesday, October 11, 2011
Late yesterday afternoon I got a message from Jim Barber at the First Presbyterian Church of Dearborn, directly across the Rouge River from campus. They had a large owl (he thought Great Horned) trapped in the basement boiler room of the church. He was at wits end -- the bird had been there for at least several days and nobody he called was taking any action. The notion of a Great Horned Owl getting down a ventilation shaft seemed pretty unlikely to me, and he told me the room was around 20 by 20 feet with high ceilings. This seemed like a difficult situation, but my curiosity, the plight of the bird, and Jim's frustration compelled me to immediately head up to the church and figure out how I could help.
Within 15 minutes I was looking in the boiler room. Not only was it big, it was cluttered with all sorts of equipment and supplies. This was the part of the room I saw when I walked in:
I decided there were two possibilities for catching the owl. One, with a long-handled net, although with so many obstacles I thought this might result in a lot of chasing around, which would stress the bird. The other was to use a bal-chatri trap, a common way of catching raptors. Bal-chatris are wire traps topped with small nooses made of fishing line. A mouse is placed in the trap, and when the raptor pounces on the trap it gets its talons caught in the nooses. The mouse isn't harmed, and the bird can be quickly released from the nooses. I figured the owl would be very hungry after three days, and this should work pretty well.
After outlining my plan, I called my husband Darrin O'Brien to have him bring a bal-chatri from home as well as a net for back up. I also called my good friend Jim Fowler. Jim has a great deal of experience handling raptors, and also spent 30 years at Greenfield Village as the head of the grounds department, rescuing plenty of birds from buildings. He would bring a long-handled net and a second bal-chatri. I went up to the RRBO banding lab on campus to fetch my banding gear.
When we all reconvened at the church, a member of the Michigan Humane Society wildlife department had shown up. He and the church employees had ambushed the owl and had it wrapped in a shirt, saving us a great deal of trouble. We took the owl from him, and after one loud screech, it settled down and stared up at Jim, who held it while we checked the bird's condition and I measured the wing.
Darrin took the bird so we could band it.
I let Jim Fowler do the honors. While it looks like Jim's nose might be in danger here, it's really the talons you have to worry about. Sure enough, it did grab Jim's thumb at one point, drawing blood.
Outside the breeding season, Barred Owls cannot be sexed, so we don't know if the owl is a male or female. But looking at the color, shape, and wear of the wing and tail feathers can help determine age.
We walked to the edge of the parking lot to release the owl. It took flight and landed in a tree, shook itself, gave us one last look, and took off toward the Rouge River and UM-Dearborn campus.
Thanks to everybody who participated in this rescue. Good luck to the owl, and to the guys who I understand will be on the roof of the church today, closing off a certain ventilation shaft...
Saturday, October 1, 2011
Thrush migration has also been dismal. Gray-cheeked Thrushes are never numerous, and Hermit Thrushes have yet to arrive, but Swainson's Thrushes (left) are one of our bread-and-butter birds. Our average for Swainson's Thrush is 70, and a number of years we have topped 150. Our lowest year we caught 24, and we are tied for that number right now. It sounds like other banding stations are also below average. South of us, Black Swamp Bird Observatory was at 131 Swainson's Thrushes as of mid-month, and their mean is 480. If you have any thoughts or observations on thrush migration in the eastern U.S., please feel free to leave a comment! Looks like we'll have to put in at least one more year to increase our sample sizes for our dietary study.
Speaking of which, many trees and shrubs are still laden with late-ripening fruit. I don't ever recall having any substantial crops of arrowood (Viburnum dentatum) or elderberry (Sambucus canadensis) into September, yet these trees have had fruit most of the month, some still coming ripe. The Amur honeysuckle (Lonicera maackii) crop, a non-native, is still only about half-ripe. On the final day of September, I found multiple plants of this species, as well as gray dogwood (Cornus racemosa), woodbine (Parthenocissus inserta), and Japanese honeysuckle (L. japonica) still blooming! This year we have large crops of wild grapes (Vitis spp.), poison ivy (Toxicodendron radicans), and non-native climbing nightshade (Solanum dulcamara). Does anybody else think fruit crops are a little tardy this year?
Good numbers of warblers, relatively speaking, are still moving through, although we have yet to see Yellow-rumped Warblers in any numbers. This past week we exceeded our high number of Nashville Warblers (above), with 60 banded so far (our fall mean is 28). Two more uncommon species were also banded this period.
Thursday, September 22, 2011
When mounted on a bird, a geolocator records light intensity data at intervals throughout each day. Retrieved later, the data can be downloaded and migration routes, pace, and destination can be determined. For species with broad breeding and wintering ranges, this can provide important information on exactly where particular breeding populations spend the winter. Given that we have long-term Breeding Bird Survey data indicating that populations of some species are declining in particular regions of North America, figuring out where these birds spend most of the year helps us identify what may be causing their declines, and helps us devise more effective conservation measures.
This fall, RRBO is placing geolocators on a sample of summer resident Gray Catbirds. This project is a joint effort between RRBO and Dr. Melissa Bowlin, who joined the UM-Dearborn faculty late last year and who is a research partner of the Environmental Interpretive Center. Dr. Bowlin's interest is in how physical traits of birds influence their migratory performance. In our catbird study, she will be looking at how the wing shape of individual birds impacts the pace of their migration. The geolocator data will allow us to determine the time it takes for each of the birds to reach their wintering destination, and hopefully where the birds stop each day, so we can calculate the rate of migration for each bird.
RRBO is interested in the approximate route followed by catbirds breeding in this area, as well as where they spend the winter. Previous data from other researchers have indicated that Midwestern catbirds winter in Central America, whereas catbirds Mid-Atlantic nesting catbirds winter in the southern U.S. and the West Indies. This information is based on small sample sizes: recoveries of 17 banded birds and 6 birds with geolocators. Our data will add to this knowledge.
The geolocators are tiny, and are carefully fitted on the birds with a flexible harness that loops around the bird's legs. The total weight of the geolocator plus the harness is less than a gram, or about 2.5% of the weight of an average catbird. The recommendation for any kind of radio transmitter or attachment to a bird is 4% or less. The geolocator rests just above the bird's rump. Dr. Bowlin has done careful studies, published in the journal Methods in Ecology and Evolution, determining the effect of drag and weight of various types and configurations of geolocators, using preserved bird bodies in a wind tunnel. The set-up we are using is the best available configuration to minimize these effects.
|A geolocator, attached with a leg harness, above the rump of a|
catbird at RRBO. The little wand pointed toward the tail is
the part with the light sensor.
|When the feathers are smoothed out, only the light wand|
As you can see, the potential for these little devices to unravel basic life history mysteries is huge. The pioneering study with bird and geolocators was done by Dr. Bridget Stuchbury and published in the journal Science. The study looked at Wood Thrushes and Purple Martins, and is summarized here. Geolocators are being used to study Bicknell's Thrushes, Bobolinks, Red Knots, Ruddy Turnstones, and Golden-crowned Sparrows, among other species. Much more information on this technology, as well as the importance of what we can discover is available at the web site of the Migratory Connectivity Project.
We plan to offer donors an opportunity to sponsor these catbirds. To be included in our fall campaign, add your name to the RRBO mailing list.
Friday, September 16, 2011
Twenty were RTHU, which we released unbanded. Subtracting those and recaptures, 216 were new birds. Thanks to Darrin O'Brien and Dana Wloch, two of my most experienced banders, we worked out a system where birds were fully processed -- measured, aged, sexed, and weighed -- in less than two minutes and we were never away from the nets for more than 40 minutes.
|In the fall, Bay-breasted Warblers usually don't show|
much bay color on the flanks. This one has a hint.
|Black-throated Green Warbler|
When there are large pushes of birds due to weather systems, it's hard to attribute inflated numbers to actual increases in populations, but a few other species have more numerous than usual this season overall (not just on the two big days). Blackpoll Warblers are much more common; our fall mean is 23, and we've banded 43 so far. Our current total of ten Black-throated Green Warblers is well above our fall mean of two and high of six. We've netted and released 52 Ruby-throated Hummingbirds. Since they are not marked some may be repeats, but it isn't too unusual to catch three to five in one net. However, the most we've netted in the past was 50, and we usually get them into October.
Things tapered off after those two big days and have more or less returned to normal. I hope to have a post up about one of our special projects within the next week or so.
Thursday, September 8, 2011
I did take a look at the previous RRBO data and compared it to our August data to see if my hunch that birds seemed to have nested a little later, based on molt patterns, was correct. I mentioned this in my previous post. I examined all hatching-year birds banded in August 1992-2010. About 13% of those birds had not yet started their first post-juvenile molt. For August 2011, it was 26%. So it does seem that a lot of the juvenile birds we caught in August were a week or so younger than in previous years.
We hope to be able to resume banding over the weekend.
Monday, August 29, 2011
The extent of this molt this year tells me that these species -- cardinals, catbirds, robins, and Song Sparrows mostly -- were a little later in fledging than usual. It could be that the big flood in May caused some birds to lose their first nest, and pushed breeding back a couple weeks. Or, good conditions this summer (warm, good amount of rainfall, lots of bugs) could mean some species attempted a third nesting.
I have heard and seen adult birds still tending their newly-fledged young. Here is a brand-new youngster I captured this week. Can you guess the species?
Another frequent nester is the Baltimore Oriole. Because they migrate so early in the season, I sometimes don't catch any in the fall. I had three in one net this week, including this adult male. Orioles are pretty sassy. This one seemed astonished, and a little indignant.
Friday, August 19, 2011
Not too many migrants were present. We caught a Yellow-bellied Flycatcher on 15 August, which was an early date for a fall migrant in Dearborn. A Chestnut-sided Warbler captured on 17 August was the only other passage migrant netted this period. I like the inquisitive look it has.
What we did have was a lot of mosquitoes. This is the worst year for mosquitoes I can remember. In fact, so many come inside with me that they are as bad inside the banding room as many typical years outside.
The coolest bird we caught was not uncommon -- a male Northern Cardinal. But it was a bird we had banded on 19 April 2001 as a second-year bird. Thus, he is now over 11 years old, the oldest cardinal we have recaptured and the second oldest bird we have ever recaptured. While 11 years falls short of the record listed at the Bird Banding Lab web site of over 15 years, it was still good to see him. Over the years he has been recaptured 21 times, but the last time was in 2009.
This is our fifth year of studying the diets of fall migrant birds on campus. We're off to a good start with our sampling of seeds in the poop of various birds. These are all from robins and catbirds.
Just about every species of fruit that is currently ripe has showed up in the samples: grape, pokeweed, glossy buckthorn, dogwood, cherry, and nightshade.
Speaking of robins, three of the six robins we've caught so far have weighed less than 60 grams and have been fairly emaciated. By comparison, only six robins out of over 3500 previously banded here have weighed less than 60 grams, and the average weight for robins is about 78 grams. Generally, I only see birds like this when they are on death's door, and often after they have been exposed to lawn chemicals. I don't have an explanation for the lean condition of these birds, but we'll be monitoring future captures carefully.
Finally, it looks like it may be a very good year, the first in some time, for chickadees. Over the decade between 1992-2002, the resident chickadee population on campus was on the decline. Last fall, there was a large movement of chickadees in eastern North America. It was notable here, and I wrote about it after our last Winter Bird Population Survey season. Clearly, many chickadees chose to stay and nest here, as they were evident on our spring survey as well. We've already banded nine, which is our average over the past nine years. Our high was 52 in 2002. As you might imagine, they are quite the little fussbudgets. I'm happy that their numbers are rebounding, but not so sure I want to band a record number of them.
A Black-capped Chickadee was the first bird banded by RRBO during our inaugural fall season in August 1992. That's right -- this is RRBO's 20th fall banding season. Stay tuned for anniversary-year news.
Monday, July 18, 2011
This has happened only a few times for RRBO: a Yellow-rumped Warbler caught in Tallahassee, FL, a White-throated Sparrow on Ontario's Bruce Peninsula, and a Northern Waterthrush in Wisconsin.
What made this American Goldfinch capture even more special was that it was captured by Antonio Salvadori.
that was caught in Ontario. Photo by. D. O'Brien.
Toni has been banding for nearly as long as I have been alive, founded the Guelph Banders Group, and bands at three locations. One is at his home in Guelph; another a property in Ermosa, just outside of Guelph; and at Colwyn Farm, northeast of Guelph near the town of Fergus.
But here's the kicker. In 2008, Toni captured and released a Blue Jay banded in the east Dearborn yard of RRBO's Julie Craves and Darrin O'Brien. He caught the jay at his Ermosa, Ontario location.
It's hard to imagine the odds of this occurring. I might expect that Black Swamp Bird Observatory would capture some of our birds, or vice versa, given their volume and location on the north shore of Lake Erie about 50 miles nearly due south of RRBO. So far, this hasn't happened.
You can read more about other out-of-state recoveries of RRBO's birds on our recoveries page, and about Toni's banding history in this PDF from the Guelph Field Naturalists newsletter.
Cross posted at the RRBO web site.
Thursday, June 16, 2011
Spring 2011 was the second wettest spring on record for Detroit, according to the National Weather Service. April was generally cool, with measurable precipitation 18 out of 30 days and a rainfall total 2.5 inches above normal. May featured normal temperatures, and 21 days of precipitation. This included a dramatic soaker on May 25-26 with over 2.5 inches of rain on campus that caused the Rouge River to peak at least five feet above flood stage (upper left in photo is the waterfall at Fair Lane Estate, inundated by the high water). The month ended up being the second wettest May on record.
Thirty species of warblers were recorded on campus this spring. This includes all 26 regularly-occurring species (at least 8 of the last 10 years), as well as the less-common species Pine Warbler (26 Apr), Prothonotary Warbler (9 to 11 May), Kentucky Warbler (10 May), and Hooded Warbler (18 and 22 May).
In general, migration was excellent this year, which has not been the case for the past five years or so. In addition to great diversity, numbers were also better. Early season migrants were especially abundant. The two eBird graphs below show two of these species, Yellow-rumped Warbler and Palm Warbler for the last five spring migrations. Lines represent the highest count of a species submitted on a single checklist from the UM-Dearborn campus during the weekly periods indicated. They show peak numbers in 2011 were much higher than in recent years (click to enlarge).
A variety of things could factor into these increased numbers, but a couple stand out, especially for the high numbers of early migrants. First, this was a La Niña year. While La Niña/El Niño cycles do not have a strong impact on our weather here in the upper Midwest (which is more influenced by the North Atlantic Oscillation), it does have a strong impact on weather where many of "our" birds winter. Namely, it was a very wet winter in much of Latin America. Wetter winters tend to have higher insect abundance, which translates into better overwinter survival for some species of birds. Thus, some species may have been more abundant this year.
Another factor could be detectability. The overall cool weather, without early hot spells, slowed leaf-out on woody plants. When trees don't have leaves, birds are simply easier to see and count. The graph below shows the accumulated growing degree days (GDD) for the period of 15 March, when woody plants here often begin to awaken, and 10 May, when we would expect many migrant bird species to be present. GDD are a measure of heat accumulation based on daily temperatures that are often used in agriculture to determine, for example, when crop species are likely to mature (data from Detroit Metro airport, click to enlarge).
As you can see, by our peak day of 10 May, the accumulated GDDs were the lower than they had been for years, which was reflected in the slow leaf-out of the trees here on campus.
Other notable birds this spring included Osprey on 10 and 23 May; five records of Bald Eagle, of which three were on campus; five records of flyover Sandhill Cranes, all from campus (there have only been 10 records in the past 10 years!); and the spate of Bobolink sightings around Dearborn between 6 and 9 May which included ten singing males in the fields at Hubbard and Southfield on 8 May.
Only two species arrived earlier than any previous record for Dearborn. They were Ruby-throated Hummingbird on 26 Apr (4 days earlier) and Indigo Bunting (27 Apr off-campus, 1 day earlier). A Blackburnian Warbler on 27 Apr tied the previous early arrival date. Two Common Loons seen over east Dearborn on 20 Mar were also early, but occasionally this species winters in the Great Lakes.
Extremes are interesting, but deviation from a more typical arrival date is probably a more accurate depiction of any shift in migratory phenology. I have 14 to 21 years of spring arrival dates for 43 species. There are a number of ways to calculate central tendency (or the "expected" middle value of a data set). For simplicity's sake in this example, I calculated the arithmetic mean, or average arrival date for each species to compare to this year's arrival dates. For these 43 species:
- Fourteen (32%) arrived on their average arrival date.
- Seven (16%) arrived later than average (the average for those species only was 3 days later)
- Twenty-two (51%) arrived earlier than their average arrival date (for those species, the average was 4 days earlier).
- For all 43 species, arrival time averaged 1.6 days earlier than "usual."
Many thanks to Darrin O'Brien and Mike O'Leary, who assisted with surveys this spring.
Monday, May 16, 2011
Saturday, May 14 was the North American Migration Count. My husband Darrin O'Brien coordinates the count for Wayne County, and as usual we covered the UM-Dearborn campus, as well as some other spots in Dearborn. It was a pretty lousy day weather-wise, and many of the migrants that we enjoyed last week had moved on. Although we were only able to thoroughly cover campus and one of the Ford fields (with quick peeks at a few other locations) we still managed to have a pretty good day.
On campus we tallied 83 species, including 19 species of warblers. None of the warblers were recorded in numbers over 10 individuals, but we had great looks at Mourning Warblers which is always a treat. Most of the warblers were feeding rather high in oak trees, typical of mid-migration as they are among the last trees to leaf out. Other highlights included a flyover Broad-winged Hawk, and the first Gray-cheeked Thrush of the season.
We spent more time than we budgeted at the Ford field in the southeast corner of Hubbard and Southfield (field #1 on this map). We ended up with 48 species there, including 13 warblers species feeding in the oaks along the margins. This field, along with several others, has been planted in a cover crop of clover. While the Bobolinks present there earlier this month have moved on, there were many Savannah Sparrows on territory or with nests, along with Ring-necked Pheasant, Eastern Towhee, and some lingering White-crowned Sparrows. One of the better birds of the day was a calling Eastern Meadowlark in field #8. This is no longer an easy bird to find in Dearborn.
Please note that these fields are now posted "no trespassing" so should only be viewed from public roads. RRBO has permission from Ford security to survey them.
One last surprise was a big roost of Double-crested Cormorants (above) at Fordson Island. Between the birds perched on the dead tree and the ones flying around the Ford Rouge Plant, we counted 102. Back at home in east Dearborn, we had one of the Pine Siskins nesting in the neighborhood.
Unfortunately, we did not have the time to walk along the Rouge River channel, or hit a couple of other birdy spots. Overall, we had 98 species (23 warbler species) in Dearborn for the day.
Friday, May 13, 2011
The chart below shows the number of species seen on campus each day since 2 May (the yellow line) as well as the number of warblers species (the blue bars). Click to enlarge.
The best day of the season was 10 May, with 95 species recorded, 25 of which were warblers. For some perspective, there are 37 species of warblers that occur regularly in Michigan (4 more are considered accidental; we have recorded all but 2 of the 41 species in Dearborn in the last 40 years). Some of the warbler highlights were a Kentucky Warbler on 10 May, our first record since 2006 of this southern species, and a female Prothonotary Warbler, which was present from 9-11 May. A gorgeous Golden-winged Warbler was also seen from 10-12 May. Closely related Blue-winged Warblers have also been present, while on 8-9 May, a hybrid of the two, a "Brewster's" Warbler, was observed; it sang a Blue-winged song. The total number of warbler species for 2011 so far is 28.
Other bird highlights of this period include a Summer Tanager and an Osprey on 10 May; a fairly early Olive-sided Flycatcher on 12 May, and two Red-headed Woodpeckers on 13 May.
We have recorded 133 species on campus so far in 2011. The total for Dearborn for the year is 151. This includes two records of Clay-colored Sparrow. One was this bird, photographed by Cathy Carroll along the Rouge River near the TPC of Michigan on 10 May.
Another was singing at the fallow sunflower field at the south side of Hubbard at Southfield. That location also hosted up to 10 male Bobolinks from 6-8 May.
I have added a box to the RRBO Latest Sightings page that includes links to bar charts for all species recorded on campus and in Dearborn which have been entered into eBird. This includes 2011 only, as well as all records input so far back to 1994. I have mostly put in spring and winter data, but am now working on summer and fall data. This is already over 2000 individual checklists. I try to add new data daily, so check back regularly.
I think migration has been terrific due to a combination of things. First, we did not get the very early warm spells that we have had the last couple of years, so trees and shrubs did not leaf out early. This has made viewing conditions quite excellent. Cool mornings have concentrated birds in sunny spots in the morning, and also resulted in many insects being most abundant near the water's edge (on campus, along Fairlane Lake). Thus, birds have been easier to find. Some credit has to be given to the luck of weather patterns, which are always the wild card. Finally, I think we are recovering from population losses that were due to the dramatic cold spell in the eastern U.S. in spring 2007 (I discussed this on the RRBO web site the following spring).
There is a lull right now, but I expect we will get one more good wave of migrants before the end of the month. Viewing conditions will be more challenging now that foliage is thicker, but do your best to get out and enjoy!