The December 2005 issue of the journal Conservation Biology has a paper on a topic near and dear to my heart (heh-heh):  deer overpopulation.  In case you missed previous installments, there was the overview of the ecological problems of too many deer, their impact on songbird populations (scroll to bottom of post), and how too many introduced deer actually extirpated black bears on an Canadian island.

The current paper also examined islands in Canada, this time the Queen Charlotte Islands, BC.  The authors looked at islands on which Sitka Black-tailed Deer (Odocoileus hemionus sikensis) had been introduced for less than 20 years, more than 50 years, as well as deer-free islands. They sampled invertebrates at the forest edge and in the interior, in the litter and below the browse line. 

Not surprisingly, abundance and diversity decreased with increasing length of browsing history, especially at the forest edge, in the vegetative layer, representing the destruction of the understory plant cover by deer.  Primary consumers which depend on the vegetation depleted by deer were most affected; true bugs (Heteroptera) were absent from islands which had a long browsing history.  Forest litter invertebrates were less impacted, with only gastropods (such as snails) decreasing with increased browse time. 

My immediate thought was how this impacts the animals that feed on these now-missing invertebrates.  The authors echoed my concerns, stating that "Such reductions most likely affects groups such as insectivorous songbirds."  The implications for my own research on migratory songbirds in urban areas leaped out at me:

• The decreases of invertebrates are more pronounced at the forest edge.
• Urban habitats are often characterized by more edge habitat, and urban forest remnants are already oversimplified and stressed by invasive species, human use, and other factors.
• Fewer deer have higher impacts in small urban forest fragments, and their populations increase quickly in the absence of hunting and predators.
• Other studies, as well as my own research, indicate that migratory birds preferentially use edge habitats during migration.
• Therefore, the reductions of invertebrates in urban forests due to deer browsing may be even greater than those found in this study, and have magnified impacts on birds that depend on these forest fragments during migratory stopovers.

Forest litter invertebrates are also important food items for migratory birds, but I didn’t take a lot of consolation in the fact that they were less impacted in this study.  The islands examined here were dominated by Sitka spruce.  While I admit I am not very well-versed in coniferous versus deciduous forest litter composition, my hunch is that the litter in an eastern deciduous forest probably has a richer, and certainly different, invertebrate fauna than in a coniferous forest. Deer might have an even more profound impact on leaf litter invertebrates in a deciduous forest setting than they did in the coniferous forest islands.

Allombert, S., S. Stockton, and J.-L. Martin.  2005.  A natural experiment on the impact of overabundant deer on forest invertebrates. Conservation Biology 19: 1917-1929.

The last post, Cowbirds 101, received a few comments which I’d like to address.  I was going to do it in the comment section as well, but not everybody reads post comments, plus, I’m trying to improve “customer service,” so here goes.

Peter wondered about the reasons for cowbird declines.  I have not been able to locate any research speculating on the reasons for cowbird declines.  I am pretty certain it does not have to do with cowbird control for endangered species.  At least in the case of Kirtland’s Warbler, multiple sources have stated that the trapping has had absolutely no effect on cowbird populations. Culling of flocks of mixed blackbirds in agricultural areas, especially during winter, might be playing a role.  I believe the primary reason is habitat loss:  reforestation of agricultural lands in particular, consolidation of remaining small farms may into large monocultures, and urbanization.

Pamela, who participated in Ontario’s Breeding Bird Atlas, noted her surprise at public cowbird vilification, and also mentioned contemplating warbler behavior and parasitism rates.  This gives me an opportunity to expand a little on the “dire threat” misconception.

A minority of all host species make up the majority of the incidents of parasitism (almost 90%).  The top ten cowbird hosts are Yellow Warbler, Song Sparrow, Red-eyed Vireo, Chipping Sparrow, Eastern Phoebe, Eastern Towhee, Ovenbird, Common Yellowthroat, American Redstart, and Indigo Bunting (Lowther 1993).  I looked through the literature, and for each species I found documentation of rejector behavior, as well as the ability to raise their own young along with cowbirds. So even the most frequently parasitized species persevere — quite well, judging by how common these species are.

Kilgo and Moorman (2004) published a large study of nearly 1,400 nests of 24 cowbird hosts from the southeastern U.S., where cowbirds have only been present the last 50 or so years and presumably have found many new, vulnerable hosts. The parasitism rate was less than 10%.

Wisecrow thought we should err on the side of caution and not take a chance with endangered species by eliminating cowbird control. In a post which will arrive early next week, I will agree with this position, but conclude that selective removal of traps is probably worthwhile, if not necessary for ecological and political reasons.

To be continued…

Kilgo, J. C. and C. E. Moorman. 2004. Patterns of cowbird parasitism in the South Atlantic Coastal Plain and Piedmont. Wilson Bulletin 115:277-284.

Lowther, P.E. 1993.  Brown-headed Cowbird (Molothrus ater).  In the Birds of North America, No. 47. (A Poole and F. Gill, Eds.).  Philadelphia: Academy of Natural Sciences; Washington DC: American Ornithologists’ Union.

The other day I introduced the topic, are Kirtland’s Warblers really in jeopardy? I posed the question because funding cuts may reduce the number of cowbird traps used in the recovery of this endangered warbler. Many people have an immediate negative reaction to cowbirds, and it’s often based on a lack of understanding about their ecology and impact on other birds. Let’s start out this series of posts by getting to know cowbirds. (A list of references and resources will follow the last post in the series.)

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Male Brown-headed Cowbird, photo by Trisha Shears.

Cowbirds (Molothrus spp.) are New World blackbirds. Five of the six species are obligate nest parasites: they lay their eggs in the nests of other birds and abdicate parental care to the hosts. The most common cowbird in North America is the Brown-headed Cowbird (M. ater). Henceforth, “cowbird” will refer to this species.

Nest parasitism has evolved in various species and families of birds due to different selective pressures. In Brown-headed Cowbirds, it is an adaptation to their formerly nomadic lifestyle. Throughout most of their history, these birds followed herds of large mammals; they were once so closely associated with bison that they used to be called “buffalo birds.” Moving with these animals, which could travel many miles a day, offered little opportunity for cowbirds to stop and raise young, so they began laying their eggs in the nests of other birds, leaving the parenting to the hosts.

Cowbirds parasitize many species of songbirds. They lower the reproductive output of their hosts in a number of ways, but primarily through two behaviors. First, female cowbirds often remove host eggs from host nests, although this varies among individual cowbirds. Second, the cowbird chicks, which may be larger and louder than the chicks of the host, out-compete the host young for food.

Host species may be classified as rejectors or acceptors, with some species having intermediate reactions to parasitism that vary depending on the individual or population. Rejectors react to parasitism by abandoning their nests (often renesting elsewhere if it is early enough in the season), ejecting the cowbird eggs from their nests, or building a new nest floor over the cowbird eggs (and any of their own) and starting a new clutch.

Acceptors, on the other hand, incubate cowbird eggs and raise cowbird young as if they were their own. Usually, broods begin as a combination of both host eggs and a cowbird egg or eggs. Cowbird eggs require less incubation than most host species, and their eggs often hatch first. This also gives the cowbird chick a competitive advantage.

Myths and misconceptions
Prior to European settlement, cowbirds were not found in the forested eastern U.S. As land was cleared and agriculture spread, cowbirds expanded their range. As new frontiers opened up to cowbirds, they found many new hosts that had not co-evolved with them, and consequently had not developed defenses against nest parasitism. Many of these host species were therefore “acceptors.” Today, cowbirds are found over most of the U.S. and southern Canada.

For generations, as people began to notice the habits of cowbirds, their behavior was not seen as the unique adaptation that it is, but as somehow evil. Cowbirds have an undeserved poor reputation as being lazy or immoral. Of course, the attitude that birds, or any other animal, can or should follow human expectations of ethical or moral behavior is illogical and unreasonable.

Armed with this misconception, people blamed cowbirds for declines in songbird populations, in particular the decline of migratory songbirds that has been the source of much concern the last few decades. Reasons for declines in bird populations, particularly migratory songbirds, are varied and complex. While cowbirds do have an impact on the reproductive success of their hosts, as explained above, but they are not the dire threat they were once thought to be.

One of the world’s leading authorities on cowbird ecology, Catherine Ortega, has said that “the assumption that parasitized nests are destined to failure is unequivocally incorrect.“ I reviewed multiple studies covering over two dozen cowbird hosts presented in Ortega’s book, Cowbirds and Other Brood Parasites. In parasitized nests, the percent of host young fledged per egg is about 21%. For cowbirds, it is around 28%. In other words, cowbirds are not much more successful than their hosts. Not all, nor even most, individuals of a host species are parasitized by cowbirds, and not all parasitized nests fail to produce host young.

Despite the fact that they have expanded their historical range, cowbirds are not, as is commonly thought, increasing in numbers. Populations have remained stable, or in some regions steadily and significantly declined, over the last 50 years. Cowbirds do not, contrary to popular belief, pose an increasing threat to songbird populations.

Humans facilitated the spread of cowbirds into new habitats, introducing them to new and vulnerable hosts. We continue to provide them with plenty of edge habitat, abundant food in vast agricultural areas and feedlots, and increasing edge habitats with opportunities for them to penetrate into shrinking forested areas. Our alteration of landscapes has helped cowbirds while simultaneously eliminating, reducing, or degrading habitat, the primary reason many species of songbirds have declined. We have been left in a situation where cowbird management has been deemed necessary to assist some species of birds.  That will be the subject of the next post.

Recently, there has been a buzz going around birding and conservation lists about some funding cutbacks for Kirtland’s Warbler management.  Specifically, some of the cowbird trapping will be reduced.  A message circulating regarding the cuts from one organization calls for urgent action, stating that if the funding cuts are allowed to stand, “the Kirtland’s Warbler will be driven to brink of extinction again.”

I appreciate the good intentions of these conservation organizations, and the bird lovers that have gotten all whipped up over this message. But I think the urgency characterized here may be overblown, due in part to the vilification of cowbirds by the public and general misconceptions regarding cowbird impact on songbirds, and the unpopularity of new research on the efficacy of cowbird control for endangered species management.

We tend to lose sight of the fact that nest parasitism is a natural process.  Would any sensible conservationist endorse the slaughter of hawks, even though doing so would undoubtedly save the lives of any number of birds or small animals?

There is more than meets the eye here, and in a series of several posts, I’d like to briefly explore three main topics: an overview about cowbirds and their impacts on songbirds, problems with cowbird control as an endangered species management tool, and the specific issues surrounding Kirtland’s Warbler recovery efforts.  Stay tuned, I’m sure my “devil’s advocate” position may ruffle some feathers.

For many years, I have judged a middle school science fair at a very affluent private school where two close friends are teachers. I always enjoy it. My fellow judge for eighth grade biological science projects is a riot, and we get to say things like, “I’m leaning towards ‘Bad Breath’ myself,” and “To do this right, wouldn’t you have to, you know, re-boot your nose?”

We judge over 50 projects, but 60% fall into the following youthful themes: germs, plant growth, music, gender, and gum.  Quite a few are combinations of those themes: what music makes plants grow faster? Which gender has dirtier bathrooms? This year, the variation “Are dogs mouths really cleaner than human mouths?” was popular. Many parents are doctors or dentists, evidenced by the number of projects involving sleep labs, blood pressure monitoring, and human teeth decaying in various beverages.

The students are required to have laptops.  No hand-lettered posters here. Participants make full use of the graphical output of their software. One poster utilized nine different fonts. Here’s a creatively lettered project title, which I still can’t read:

Nearly every poster uses multiple eye-popping colors. There is rarely a monochrome, single-dimension graph. You just don’t see results presented like this in scientific journals these days:

So what are tomorrow’s scientists working on?  I’ve assembled a list of materials and a procedure section; these are actual examples from the projects I reviewed this year:

Materials

• Raw hamburger
• Three types of shoes
• Modeling clay
• Little boxes
• 15 male humans
• An exciting paper on anything of your choice
• 216 beet plants
• A little bit of sunlight
• A saddle
• Loose leaf paper
• One hamster
• Three different fingers to test
• Paper towel (each cheese will be on it)
• Human source of mouth bacteria

Procedures

• Put on latex gloves.
• Dampen your swab with distilled water.
• Get permission from Mrs. Thayer.
• Collect urine from my two St. Bernards
• Stop at Jack’s Party Store and buy the same brand of nightcrawlers every time.
• Let dry.
• Wait until the ants come out.
• Stick the thermometer in the person’s mouth.
• Bring cheese home.
• Do this for two weeks.

The projects might be basic, or esoteric, but these young scientists make up for their inexperience with their bald and honest assessments of their own work. Maybe science would move forward more quickly if we quit trying to manipulate results or try to make ourselves look good, and instead submitted the kind of straightforward self-evaluation that this student did in his Discussion:

I will be frank.  This experiment was by no means perfect. Not even close.  At times, I felt sure my hypothesis would fall flat on the ground, the results not at all matching my hopes, but somehow I did succeed. I still can’t believe it, but I know I clearly did something right.  Let’s start with that…

However, plenty of things went wrong, or at least strangely. …I will never really know what those numbers could have been with a different machine.

I certainly hope that the next person to try this test, armed with the knowledge I now know, can achieve more conclusive results than I did.

It might eliminate the need for peer review altogether!

That’s all I have to say about my experiment.

Oliver Sacks, a neurologist, has written some fantastic books. Most notable (my favorites) are his compelling accounts of people with unusual neurological disorders: The Man Who Mistook His Wife for a Hat, The Island of the Colorblind, and Awakenings (made into the movie starring Robin Willliams). Sacks is a gifted writer. These books are intriguing not only because of their unusual subject matter, but because Sacks can explain the medical science behind them clearly, and, even better, conveys his compassion for the human beings that have these conditions, and what we can learn about our own lives through their stories.

Oaxaca Journal is a departure from these books. It’s a diary of a week-long trip he took to Oaxaca, Mexico with the American Fern Society.  Other trip participants are more keen botanists, and Sacks seems to operate more on the periphery, although the text is loaded with the names of many fern species they encountered; many are illustrated by simple pen-and-ink drawings.

As expected, the best parts of the book for me were when Sacks examined local culture. As he notes early in the book, “How crucial it is to see other cultures, to see how special, how local they are, how un-universal one’s own is.”  This is a philosophy I embrace, but I was a little disappointed that Sacks did not go into the depth I might have expected, based on the insight he displayed in previous books.

Oaxaca Journal was, in fact, a pretty light read.  You’ll learn something of Oaxaca (the description of the truly gigantic Tule tree in Santa Maria del Tule is enough to make me want to go there), and if you are into ferns or botany, you’ll find the book especially enjoyable. But you won’t find the same attention to detail, philosophical dissection, or intellectual curiosity that is a hallmark of Sacks’ previous work. Sacks is only 72, but he comes off as a bit tired in Oaxaca Journal.  I hope he has more of the “old stuff” still left in him.

The other day I posted on reporting neck-collared Canada Geese.  Since then, I’ve come across another group of geese near home, of which ten had collars.  Remarkably (or not, site fidelity is one thing we learn from these types of resighting projects), seven of them were geese I had previously seen and reported in past years.

One was a white-collared goose (here she is).  I originally saw her here in town December 29, 2004.  She had been collared in extreme northern Ohio in 2001.

The rest were all orange-collared geese.  One had a collar that looked very faded, and its leg band was also very worn.  A check of my records indicated I had seen it here in November 2003.  It had been banded (like all the orange-collared geese I’ve found) on Akimiski Island, Nunavut.  And yes, it was old; it was originally collared in July 1994.

The five other familiar geese I had found all together here in town on December 20, 2004.  Once again, they were hanging around with each other.  And they had all been collared and banded on the same day — July 26, 2001 as adults on Akimiski Island!

It will take a few weeks for me to hear about the remaining three geese. The codes on the collars were a different alphanumeric sequence, so while I fully expect them to be Akimiski birds, they will be from a different time.  One of them (left), I’m going to bet, will also be an older bird, as it has the same faded collar and worn leg band as the other old one.

Belle Isle Park, Detroit

New York’s Central Park was not the only magnificent city park designed by Fredrick Law Olmstead.  The largest city-owned park in America, Detroit’s own Belle Isle, was also an Olmstead work.  Located in the Detroit River (click to enlarge maps), it is 2.5 miles long and 985 acres, with lakes, canals, woodlands, and wetlands. There is a conservatory, but the aquarium and zoo have been closed due to Detroit’s dire financial problems.  In fact, many of the facilities, dating back to the city’s acquisition in 1879, are in sad disrepair.  But it is still one of my favorite places in the city; we like to bring visitors there to show them the beautiful and historic side to Detroit that is so often neglected, even by lifelong residents.

There is always a lot of activity on Belle Isle.  It can be overwhelming gridlock in summer, but much of the year there are mostly scores of walkers, runners, bike riders, skaters, nature lovers, and sightseers.  Yesterday was another abnormally warm November day, and my husband and I headed to Belle Isle to look for waterfowl and perhaps some stray Cave Swallows (Petrochelidon fulva pelodoma). We found nothing unusual, but had 15 species of waterfowl, and recorded the neck collar numbers off of 15 Canada Geese.

Collared Geese

In addition to leg banding, geese are sometimes outfitted with colored plastic neck collars inscribed with alphanumeric codes (and sometimes radio transmitters).  The easy visibility of these collars translates to increased reporting by the public, which helps researchers gather more information on the movement of the geese. Both Canada Geese and the white geese (Snow and Ross’s) are regularly collared.

I faithfully report collared geese. So far, we’ve only seen collared Canada Geese in this area, and the collars are most frequently green with white codes or orange with white codes.  The last couple of years, we’ve seen white collars with black codes.

Green and white collars are from birds collared by the Michigan Department of Natural Resources, usually here in Michigan, but occasionally in southwest Ontario.  One of the green-collared geese we saw yesterday was originally collared on Belle Isle in 2002, and we first saw it this past May on the island, with a brood of youngsters. Another was one we saw on Belle Isle last November, which was collared in Ontario in 2002.

Orange collars are Canadian Canada Geese.  So far, every single orange-collared goose I have reported from southeast Michigan (over 30) have been collared on Akimiski Island, in James Bay, Nunavut (formerly part of the Northwest Territories).  A number of them show up around here each fall.  One of the orange-collared birds from yesterday was, once again, seen by us last November on Belle Isle; it was collared on Akimiski in 2002.

White collars are Ohio birds.  I’ve only encountered one before, so we’ll have to see if any pattern emerges when we hear back about these birds. The most interesting collared goose I ever found was one with a white bib collar (cone-shaped).  It had been banded five years previously in Maryland.  Who knows what it was doing here!

You, too, can play this game. You can report collars directly to the USGS Bird Banding Lab online.  While most collared geese also have leg bands, it’s not necessary to have the band number, just the color of the collar and code, and an accurate reading of the 3 or 4 digits.  This works for Canadian collars, too.  You’ll get a certificate back with all the information on the original capture of the bird.

On November 7, 1805, the Corps of Discovery reached the estuary of the Columbia River.  Mistaking it for their goal, the Pacific Ocean, Corps co-leader William Clark writes in his journal: “Ocian in View! O the joy!”  Although November 7 did not really signify the day the Corps reached their western terminus (that took until the 19th), the popularity of this (inaccurate) quote has solidified this date as the anniversary of the success of the Lewis and Clark expedition.

Two hundred years ago today.

I am frequently amazed at the stunning ignorance of most Americans of their own history.  The journey of Lewis and Clark’s Corps of Discovery is one of the greatest adventure stories of all time.  It seems to me that reality-addicted, thrill-loving Americans would love the saga if only for its dramatic themes of hardship, adversity, and danger.  Patriotic Americans (the now-common  type, with a different definition of patriotism than mine) should embrace it for its proof of our pioneers’ ingenuity, courage, and toughness. Yet despite this being the Corp’s bicentennial, many Americans are woefully unaware of the details of this remarkable trip.

Entertainment aspects aside, there are dozens of lessons to be learned by a careful reading of good accounts of the Lewis and Clark expedition.  And none are more relevant today than the simple contrast of what the Corps saw and recorded about the environment, flora, and fauna of the United States on their traverse of the country, and what it looks like today.

Just two hundred years later.

Recall, these were the first white Americans to explore the western half of the continent.  They had only crude maps and no real idea of what lay ahead of them. West of St. Louis, the human population probably did not exceed the numbers of present-day New York, New Jersey, and Massachusetts.

The Corps reported encountering at least 37 Grizzly Bears, which has been calculated to represent over 10,000 grizzlies in the U.S. at the time; today the population is under 400. Standing on one hill, they could see 10,000 bison. Beaver were found “on every bend” of the Missouri River. Great numbers of Sharp-tailed Grouse were found near their first winter quarters at Fort Mandan. The most recurring theme, in fact, in the narratives and journals of the expedition is the staggering abundance of wildlife encountered by the Corps.

Only two hundred years ago.

Several years ago, I attended a conference in Portland.  As I flew over the same Great Plains explored by this incredible expedition, I looked down at the extensive evidence of the hand of man upon the land. Few expanses appeared untouched.  During a break in the conference, I visited Fort Clatsop, where the Corps spent the winter of 1805-06. With my heart in my throat, I reflected on what we have done to this beautiful land in just two hundred short years.

We can only appreciate our losses if we know and understand where we started, and can see the profound changes we have wrought.  We owe a huge debt to Meriwether Lewis, William Clark, and the other members of the Corps of Discovery for leaving us with detailed accounts of our natural history. Every person who considers themselves a conservationist — indeed, every American — should take the time to truly comprehend the story of the Corps of Discovery.  It is our story. Without knowing the beginning, we cannot write the ending.

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Books & DVDs:

• If you can only read one book about it, make it Stephen Ambrose’s excellent Undaunted Courage.
• Lewis and Clark, Pioneering Naturalists
• Our Natural History: the Lessons of Lewis and Clark
• Ken Burns’ Lewis and Clark: The Journey of the Corps of Discovery

Web sites:

• Discovering Lewis and Clark
• Lewis and Clark at PBS
• List of animals first discovered by the Corps