I’ve been looking forward to reading Avian Conservation and Ecology, a new open-access electronic scientific journal sponsored by the Society of Canadian Ornithologists and Bird Studies Canada. I was not disappointed in the first issue, as it has an interesting and informative essay on the Ivory-billed Woodpecker entitled Rediscovering the king of woodpeckers: exploring the implications.[1]

The paper takes the rediscovery at face value. There’s not a consensus that this species was actually rediscovered, but that doesn’t take away from the point of the essay. In the introduction, authors Jeffrey Walters and Eileen Crist, both of Virginia Tech, note that “The emotion and exposure associated with the Ivory-billed Woodpecker’s plight guarantees that it will impact conservation in the United States, and perhaps elsewhere, far more than any other single species in the foreseeable future.”

The main question posed by the essay is, “Are the biological problems this case presents even solvable?”

These problems lie in two arenas: habitat and population size. The decline of the woodpeckers was due to habitat loss. Recovery of animals that have declined from this threat is much more difficult and less frequently achieved than recovery from threats that impact “vital rates” (e.g., reproductive decline due to pesticides). The challenge is compounded by the fact that the Ivory-billed Woodpecker has very large area requirements. It is often easier to address habitat quality versus habitat quantity. Acquiring lots of habitat often becomes a political hot potato,as is exemplified by the situations with California Gnatcatchers and Spotted Owls.

Second, the Ivory-billed Woodpecker, if it actually still exists, has a critically small population. Our general approach to endangered species management recognizes that small populations are extremely vulnerable to a host of threats. Our strategies aim for viable populations, which typically means a minimum of hundreds of individuals with as much genetic diversity as possible, spread over a geographic range that insulates against a catastrophic event wiping out the whole species. A rough “rule of thumb” is that a population of 500 is needed to maintain overall genetic variability. [2]

Is it even possible to restore a population of 500 Ivory-billed Woodpeckers? Other species have recovered, at least partially, from critically low numbers (the essay gives the Guam Rail and Takahe as examples), but these species had declined due to “vital rates” threats, and recovery efforts included captive breeding and translocation, which, the authors note, are techniques that are not possible with the Ivory-billed Woodpecker. If we settle for a smaller population, does that undermine current policy regarding the unacceptability of small populations?

The paper is fairly non-technical and short, give it a read. It is probably just the beginning of thoughtful analyses of the conservation implications surrounding the Ivory-billed Woodpecker.

Finally, there may be more news on the rediscovery. Mike’s Birding and Digiscoping Blog pointed out a post on Laura Erickson’s blog in which she hints at the fact that there may have been more sightings by the Cornell team in Arkansas; the statement was later changed, and when I went to look for it, I couldn’t find it at all.  Laura is on an Ivory-billed Woodpecker quest. It’s unclear whether she is part of an official Cornell team, but as I recall she has been in contact with them, or has a relative directly involved, or something like that.  Anyway, they may have asked her to edit or remove the post.  We’ll see.

[1] Walters, J. R., and E. L. Crist. 2005. Rediscovering the king of woodpeckers: exploring the implications. Avian Conservation and Ecology 1(1): 6. [online] URL: http://www.ace-eco.org/vol1/iss1/art6/

[2] Thompson, G.G. 1991. Determining Minimum Viable Populations under the Endangered Species Act. U.S. Dep. Commer., NOAA Tech. Memo. NMFS
F/NWC-198. 78 p.

Over the weekend, an Ivory Gull (Pagophila eburnea) was found near Point Pelee, Ontario. The sighting of one of these birds in the United States always creates a sensation, because it is a bird of the high Arctic, and fewer than 14,000 pairs are thought to exist.

I saw an Ivory Gull about 10 years ago, also in Ontario, on the Canadian side of the St. Clair River. I was jarred out of sleep by an early phone call on Christmas Eve morning by a birder friend. Holiday plans interrupted, we immediately went to the bird. We watched this delicate and apparently lost waif for quite awhile. It seemed at home on the shifting river ice, feeding on the thawed octopus someone had tossed out for it to eat (we Detroiters are well-known for throwing octupi on ice). I remember wondering about this beautiful bird, how far it had traveled, and whether it would find its way home.

Perhaps I should make the trip to go see the Point Pelee bird. It may be my last chance. Not just to see it in the Great Lakes, but to see it anywhere on earth. For the Ivory Gull has recently undergone one of the most dramatic population declines of any bird species in North America, and nobody is quite sure why.

First, the evidence of the decline of the Ivory Gull was based on anecdotal reports. Ivory Gulls breed in very rugged and remote locations, but are (or were) commonly seen during migration. Therefore, residents of the High Arctic in eastern Canada were surveyed. Those in Resolute Bay used to see Ivory Gulls at their local garbage dump, but none were seen in 2000-2002. In the early 1980s, 200-300 Ivory Gulls were found at the Grise Fiord dump. Numbers declined in the next two decades, and now the gulls are no longer found at the dump. In Arctic Bay, where the gulls occur along the floe edge, comments from residents were somewhat mixed.

Follow up aerial surveys in Arctic Canada conducted through 2003 unfortunately corroborated the impressions of the residents. Nearly all known Ivory Gull colonies were visited. Several of the largest were completely devoid of Ivory Gulls, and others had significantly fewer gulls than previously observed. Some new colonies were discovered, but they were sparsely populated. In all, the surveys recorded an 80% decline in the number of nesting Ivory Gulls since the early 1980s. While it is conceivable that the birds moved completely out of the eastern Canadian Arctic, it is unlikely, as Ivory Gulls rarely move more than one or two kilometers when they change colony locations.

Ivory Gulls also nest in the Russian and Norwegian Arctic islands, but a lack of funding has prevented a full census since the mid-1990s. The last survey of a major breeding region in Russia’s western Franz Josef Land in 1996 came up empty.

There are many suspects in the decline of the Ivory Gull, but none hold the smoking gun. Climate change may be a factor. The gulls nest at such high latitudes that the retreat of food sources along with offshore ice, which impacts other Arctic seabirds during the breeding season, probably does not affect Ivory Gulls. But the increased sea ice on their wintering areas due to changing regional temperatures may be starving them. Hunting could be reducing Ivory Gull numbers, but most Arctic residents don’t harvest them regularly.

A serious threat is chemical contamination. Arctic animals carry higher loads of toxins — pesticides, lead, mercury, and PCBs — than nearly any other creatures on earth. These airborne chemicals, which will volatilize in most climates, finally settle only in very cold conditions like those found in the Arctic. They quickly accumulate in the food web. Animals near the top, even Ivory Gulls which often feed on seal and whale blubber, concentrate these toxins at startling levels. Coincidentally, I have just started the book Silent Snow: The Slow Poisoning Of The Arctic chronicling this situation; I will review it when I’m finished. From what I’ve read so far, it seems a good bet that toxic burdens are hindering reproduction or survival of Ivory Gulls, especially if the birds are stressed by changing climatic conditions. The same air currents that helped bring us this special visitor have also provided the Arctic with continued malignant doses of our most unwanted poison pollution.

For the majority of us, the dire problems in the Arctic are “out of sight, out of mind.” That is, until a pure white bird comes along, an emissary from the top of the world, and reminds us that faraway lands are only wingbeats away.

Gilchrist, H.G. and M.L. Mallory. 2005. Declines in abundance and distribution of the ivory gull (Pagophila eburnea) in Arctic Canada. Biological Conservation 121:303-309.

Haney, J.C., and MacDonald, S.A. 1995. Ivory gull, Pagophila eburnea. In: Poole, A., and Gill, F., eds. The Birds of North America, No. 175. Philadelphia: The Birds of North America, Inc.

Krajick, K. 2003. In search of the Ivory Gull. Science 301:1840-1841.

Mallory, M.L. , H.G. Gilchrist, A.J. Fontaine, and J. A. Akearok. 2003. Local ecological knowledge of ivory gull declines in Arctic Canada. Arctic 56: 293-298.

Photos courtesy Environment Canada.

crisp brown leaf, wind-blown
flake of bark, falling from tree
nope, wrong: brown creeper

The diminutive Brown Creeper (Certhia americana) is notorious for being unobtrusive.  Even the creeper’s sweet, clear, musical song can be frustratingly difficult to hear due to its high pitch.  Although creepers busily hunt for tiny insects and spider eggs hidden in the crevices of tree trunks and branches, they are difficult to locate, blending in harmoniously with the substrates on which they forage.

I remember my first up-close encounter with a creeper, as a young girl.  One hit our window, and for a short minute, I held the temporarily stunned bird in my cupped hand.  How could plumage, painted from such a monochromatic palette, be so achingly jewel-like and gorgeous? My contemplation was brief, as the bird hastened from my hand and disappeared. Everafter, whenever I discovered a creeper on a tree, nearly indistiguishable from ordinary bark, I wondered: Had I imagined the exquisite beauty?  But, no.  Nature imitating nature often brings us the most surprising and creative examples of her artistry, frequently in small packages like the delicate Brown Creeper.

Photo by Cindy Mead of Woodsong Nature Photography.

Obligatory tally of 2005 birds:

• Number of species seen: 513
• New life birds: 201
  • Last life bird: Cinnamon Woodpecker (Celeus loricatus), Pipeline Road, Gamboa, Panama

• Total life birds: 887
• otal ABA-area birds: 568
• Total state birds: 304
• Total birds in my home city: 206
• Total birds at my place of work: 183

What might be my first life bird of 2006?   Hmm, I’ll say West Indian Whistling-Duck.  Yep, headed for the West Indies in two weeks.  According to the National Weather Service, we’ve had only 14 minutes of sunshine here since mid-December.  I’m more than ready for sun and warmth!

This past week I participated in one of several Christmas Bird Counts that I do annually. I’ve done counts here in Michigan on sunny, cloudy, snowy, rainy, raw, and balmy days, but never on a day that included all of the above, plus thunder, lightning, and a rainbow (all with the temperature under 40 degree F). Very strange.

We had a nice diversity of species, including a Gray Catbird, which is pretty rare in winter around here.  It was camping out in a buckthorn tree, which harbor about the only berries left at this point (fruit being the main food of a winter catbird in these parts).  This brings us to the most unusual sighting of the day.

As we tromped through the woods, we came across a bright blue stain in the snow, as if someone had spilled windshield washer fluid.  A rabbit turd was next to it.  We thought this was weird, but figured there must have been some litter that had leached blue ink beneath the snow, and that the rabbit poop was coincidental.  Then we found another identical stain and turd.  And another.  I quit counting after twenty or so.  Not every pile of bunny pellets had a blue stain, but all blue stains had some poop. Obviously, this was rabbit urine. As usual, we were in an urban area, next door to a chemical plant, in fact. Was there a family of toxic rabbits running around, voiding blue pee?

I came to learn that this neon cerulean tinkle is a result of rabbits consuming buckthorn (Rhamnus cathartica), a highly invasive tree in North America.  One of the chemical constituents is excreted in the urine, and within a short time turns blue when exposed to sunlight.

The only credible mention of this was an anecdotal account on the Ontario Woodlot Association web site. The author observed this blue pee and experimented by feeding domestic rabbits and goats buckthorn and other shrubs.  Blue pee resulted only after buckthorn consumption. Blue urine has not escaped the notice of other folks, but nearly all other explanations I found on the Internet were remarkably asinine, including people spitting out mouthwash (I know I often take advantage of a nice stroll in the woods to bust out the Listerine) and Bigfoot piss.

Because buckthorn is such an important invasive species and so common in urban areas, I am especially interested in the often unexpected ways it impacts other organisms (like the ecosystem-altering way it interacts with non-native earthworms). I have done quite a bit of research on buckthorn, but mostly as it relates to birds consuming the fruits, not mammals eating bark and shoots.  I did a literature search, and found nothing on this phenomenon, which must, of course, occur in the native Eurasian range of buckthorn as well.

I’m surprised that I’ve not found blue urine stains at my own study site, which is jammed with buckthorn and has no shortage of rabbits.  I figure it must have to do with the fact that buckthorn is not a preferred forage for mammals (due to the many phytochemicals it contains, one of which apparently causes this reaction).  If the rabbits aren’t eating it, they aren’t peeing it. It’s also possible that not all rabbits would void blue urine after eating buckthorn.  Perhaps only certain individuals are unable to metabolize some chemical constituent. Or the reaction may require consumption of a certain amount, or the combination of buckthorn and some other food.

I’d be really interested in any research results on this, if anybody has some references.

The Auk is the journal of the American Ornithologists’ Union, and it publishes some pretty dense material. The last few years, it has featured an increasing number of papers on phylogeny, taxonomy, and genetics. This stuff tends to sail right over my head like a frigatebird on a stiff wind.

A genetics paper by Edelaar et al. in the recent issue caught my eye because it addressed a very interesting phenomenon: the direction in which the bills of crossbills cross.

Crossbills (Loxia spp.) are finches of coniferous forests, of which two of the five species are found in North America: the Red Crossbill (L. curvirostra, shown here in this great photo by Michael Woodruff) and the White-winged Crossbill (L. leucoptera). The tip of the lower mandible in crossbills crosses the upper; no other birds have naturally-occurring crossed mandibles. This configuration is an adaptation that helps the birds pry open partially closed conifer cones to extract the seeds, their primary food.

The lower mandible may cross either to the left or right of the upper, and the two forms occur at an approximate 1:1 ratio in most species. Below, we see Red Crossbills in which the top bird is a “lefty” and the bottom is a “righty.” (The bill sizes are different, too, indicating that these individuals probably represent two of the eight or so different races of Red Crossbill, some of which may one day be considered distinct and separate species. Bill sizes are correlated with the type of conifer each race favors, e.g., larger bills being optimal for larger cones.)

Crossbills usually feed on cones that are still attached to trees. The tip of the lower mandible has to be pointed towards the axis of the cone in order for the scales to be effectively pried open. Unless the bird can move all around the cone (or remove it), it is limited to consuming seeds from one side of the cone.

The prevailing theory on how the 1:1 ratio is maintained was presented by Benkman (1996) and is summarized by Edelaar et al.:

“Birds that visit cones previously foraged on by birds with the same mandible crossing direction would…suffer from reduced food intake because of resource depletion” they explain. Ergo, lower survivorship for those birds, a situation favoring birds with the other (rarer) mandible crossing direction. This give and take results in a frequency-dependent selection that is stable at a 1:1 ratio.

This whole scenario hangs on the assumption that bill crossing direction is heritable. This has not really been tested. Observing nests in the wild to record bill directions of parents and chicks is labor intensive. And while most songbirds appear monogamous, many species actually engage in “extra-pair copulations” (they cheat with neighbors), so the parents of all the chicks in a nest may not be the birds that rear them.

The Edelaar et al. study examined the offspring of 31 pairs of captive crossbills of four species, kept away from their horny neighbors. They were unable to find evidence of heritability in bill crossing direction. Alas, however, they noted that their sample size was too small to be statistically powerful, and that nearly every pair was made up of one “lefty” and one “righty.” The authors noted that, on average, the expected bill crossing direction ratio of the offspring of these pairs would be 1:1, unless there was a strong sex linkage in heritability of bill crossing direction.

It’s difficult to imagine how the crossing direction is not at least partially genetically determined. While crossbills have straight bills for about two weeks after hatching, during this period they are still being fed by the parents and the chicks are not exposed to cones, so it is not an adaption to local resources. If the direction is random, deviations from the 1:1 ratio, seen in some populations of crossbills, would be hard to explain. What am I saying? This is hard for me to explain! Geneticists and evo-devo types are welcome to contribute clarifying thoughts and elucidations in the comments.

Crossed bills in crossbills are an obvious physical trait. As it turns out, there are also interesting behaviorial dichotomies in the avian world, including “footedness” in parrots and sparrows that favor one eye. Topics for a future post!

Benkman, C. W. 1996. Are the ratios of bill crossing morphs in crossbills the result of frequency-dependent selection? Evolutionary Ecology 10:119-126.

Edelaar, P., E. Postma, P. Knops, and R. Phillips. 2005. No support for genetic basis of mandible crossing direction in crossbills (Loxia spp.). Auk 122:1123-1129.

Groth, J. G. 1992. Further information on the genetics of bill crossing in crossbills. Auk 109:383-385.

I don’t know a hell of a lot about anthropology or pre-Columbian Latin American history.  And like most everybody else, my knowledge of what North America was like prior to European contact consisted of the usual glowing descriptions of pristine habitats and wide expanses of wilderness where a squirrel could scamper from Illinois to Virginia without touching the ground.

1491 sure blew that notion out of the water, and opened my eyes to new ideas about how the Americas looked before the year 1492.

Very well-written, thorough, and thought-provoking, 1491 discusses how  humans came to and lived upon this continent — and the evidence presented indicates it was much earlier, from different directions, and with far greater impact than traditionally believed.

Author Charles Mann covers migration routes to North America, the origins of other New World people  (especially interesting in light of recent news that ancient skulls unearthed in Brazil resemble aboriginal Australians), and recent, much-elevated estimates of native populations before 1492. But it was the accounts of indigenous technology and profound environmental transformation that I found most provocative.

Although sometimes lengthy and detailed, treatments of many ancient societies, such as the Maya and Inca/Inka, are fascinating and easy to absorb even for the uninitiated reader.  I had no idea of the level of sophistication that characterizes some of these societies.  I was intrigued to learn what a complicated and significant accomplishment it was for pre-Columbian people to develop maize, considered one of the greatest feats of genetic engineering humans have yet achieved.

Compelling for me were the discussions on how pre-contact people altered and shaped the environment.  Far, FAR from living lightly on the land, they made sweeping alterations that left little untouched. Native Americans (north of the Rio Grande) made constant use of fire, providing forage for herbivorous animals which they hunted.  Through their use of fire, they were responsible for bison occupying eastern forests (if you consider woodland bison distinct from plains bison, they even shaped a species).  When disease and conflict reduced the fire-utilizing human native populations, areas quickly reverted to the dense, rather than open, forests which most early historical accounts describe.

The sections on how Amazonian Indians managed the rainforest by planting “orchards” of various palms and fruiting trees, and nurturing long-term crops from notoriously poor, lean tropical soils by tending constantly-smouldering fires in a form of slash-and-char agriculture was nothing short of a revelation to me.  A minimum of an eighth of non-flooded Amazonian forest is anthropogenic — shaped by humans.  This is an astounding figure.

These were just a few of the things I learned in 1491. Mann turns to (and often ends up in the field with) many experts — anthropologists, archaeologists, historians, botanists, political scientists, mathematicians, geneticists, medical researchers, geographers, ethnographers, chemists, and agriculture, ceramic, and textile specialists.  Yet he is able to orchestrate this vast collection of knowledge and pull it together in a coherent, scholarly yet informal, and engrossing fashion.

I love books that torpedo sacred cows, tear down long-held assumptions, and make me look at things in a different way.  1491 did all this.  What a wonderful surprise to pick up a book outside my field, expecting only a change of pace, to discover plenty of material that gave me new perspectives and added richness and depth to my area of study, ecology. Understanding today’s ecological issues requires just this type of cross-disciplinary vision.

Some will call this book revisionist or even speculative, but 1491 is carefully researched and documented, balanced, and persuasive.  New, challenging ideas deserve wide exposure and debate.  If you or someone you know likes a little intellectual provocation, by all means get a copy of 1491.

I am, at long last, concluding the cowbird/Kirtland’s Warbler series which began with a brief Introduction, went on to provide an overview of cowbird ecology in Cowbirds 101 and Responses to comments on Cowbirds 101, moved to discuss some Problems with Cowbird Control in the management of endangered species, and most recently introduced the poster-bird of cowbird control in rare bird management in Kirtland’s Warbler 101. I will try here to bring it all together and put a bow on it.

Experts agree that habitat availability is the primary limiting factor of Kirtland’s Warbler populations. The surge in warbler numbers when the Mack Lake burn habitat “came online” is strong evidence of this. It is assumed by many that the warblers would not have survived as a species to occupy this chunk of habitat had cowbird control not been implemented. Rothstein and Peer (2005, references below) note, “…though it has been suggested that cowbird control saved the Kirtland’s Warbler from extinction, there is not conclusive evidence confirming this suggestion.” They go on to add:

…it requires an odd coincidence to suggest that the Kirtland’s Warbler was headed towards extinction only to be saved by cowbird control just when its population happened to be at the carrying capacity it would have for the next 18 years.

There are many factors limiting populations of the warbler on the breeding grounds. Even long-time warbler researcher Harold Mayfield acknowledged this, and noted in his book The Kirtland’s Warbler, “Therefore we must not suppose that eliminating the cowbird would bring to fledging all the young whose loss is statistically attributable to cowbirds.”

The truth is, we don’t exactly know what would have happened in the absence of cowbird control or, more importantly, exactly what would happen if we reduced it now.

The historical data on cowbird parasitism, which led up to cowbird control, relied heavily on information summarized by Mayfield in his book, which was published in 1960. All the data is based on studies done “at various times” between 1932-1957. No scientific methodology was presented in the book. While the average rate was given as 55%, the annual rates varied from 18 to 88%. Sample sizes were small. There is really no telling how accurate the conclusions reached from these studies really are. I was told by a member of the recovery team that we don’t know how much parasitism the warbler can withstand and still maintain stable numbers. For some other endangered species, this threshold is between 20 and 40%. It would be less expensive to manage for, say, a 30% parasitism rate than for a 5% rate, but we don’t know what rate we should be aiming for. If the exact current parasitism rate is known now, I have not found it in the literature.

This type of research is apparently simply not being done, and hasn’t been done for years. I could only find 26 papers on Kirtland’s Warblers published since 1970 in major peer-reviewed journals, of which only two or three addressed parasitism and reproductive success specifically. These appeared prior to 1990. This type of detailed research on reproductive success (which would also help us identify predation rates and other causes of reproductive failure) requires labor intensive field work spanning multiple breeding seasons, for which the funding and resources have not been available. One government biologist, a participant in Kirtland’s Warbler recovery efforts, told me that this research really needed to be done, and he would choose to do it if money were available — including conducting it on subsets of warblers in which cowbird control had been withdrawn. In 2005, there was less funding for cowbird control, and fewer traps were deployed. The impact on the warblers? We don’t know, because there were no researchers studying what happened.

That is the most surprising and sobering part of the Kirtland’s Warbler recovery story. It is not that funding may be cut to the cowbird control program, it’s that there are not funds to adequately understand all of the current ecological dynamics.

I don’t think cowbird control funding for Kirtland’s Warblers should be cut, although I don’t think a reduction would be a disaster. In addition to the fact that our paranoia may not be based on reality, there are a couple of other reasons for optimism. First, we know that the impact of cowbirds on their hosts declines as host populations increase. Not only has the warbler population shot up since cowbird control began, according to Breeding Bird Survey data, cowbird populations have been declining in Michigan since the 1960s.

Second, according to one of my sources that works with Kirtland’s Warblers, the birds are also beginning to occupy areas with less agriculture in the surrounding landscape. This is good, because cowbirds prefer to feed in open areas and are attracted to agricultural settings. A study done in northern Michigan found that the probability that cowbirds would occur at a site was over 3 times greater when agricultural lands were present within 3 kilometers. Indeed, this person rarely saw cowbirds in these plots. Warblers nesting in areas away from agriculture are probably less vulnerable to parasitization.

My goals for this series of posts was to explain cowbird ecology, help people see that they are not a dire threat to most of their hosts, and that cowbird control as a management tool for endangered species is not as straightforward as it might appear on the surface. This is perhaps especially true for Kirtland’s Warbler, although each species has its own unique issues.

So the messages that went out from conservation organizations, which prompted this series, were correct to sound an alarm. The alarm was a little off-mark — it’s not the cutting of funds for cowbird control that is the real threat to Kirtland’s Warblers, it is the lack of adequate funding for the full complement of research and management that is required for us to effectively help this emblematic and charismatic little bird.

They were correct, too, in that we need to let those that hold the purse strings — Congress — know that we want endangered species programs to be strengthened, not weakened, and we want both research and management fully funded. Budget cuts are not all borne out of a lack of tax dollars, they are choices which reflect our values as a nation. It is up to us to let the people we have elected to Congress know where we want our money spent, that we value birds and biodiversity, not bacon and bombs.

The data in this series of posts was found in the following references:

• Mayfield, H. F. 1960. The Kirtland’s Warbler. Bloomfield Hills, MI: Cranbrook Institute of Science.
• Mayfield, H. F. 1992. Kirtland’s Warbler. In The Birds of North America, No. 19. (A. Poole, P. Stettenheim, and F. Gill, eds.). Academy of Natural Sciences and the American Ornithologists’ Union.
• Mensing, C. J. 2004. 2003 Brown-headed Cowbird control and Kirtland’s Warbler tour report. U.S. Fish and Wildlife Service, East Lansing Field Office.
• Morrison, M. L., L. S. Hall, S. K. Robinson, S. I. Rothstein, C. D. Hahn, and T. D. Rich, editors. 1997. Research and Management of the Brown-headed Cowbird in Western Landscapes. Studies in Avian Biology No. 18. Cooper Ornithological Society. And this paper in particular:
  • Stribley, J.M. and J. B. Haufler. 1999. Landscape effects on cowbird occurrences in Michigan: implications to research needs in forests of the inland west. Pp. 68-72.
• Olson, J. A. 2002. Special animal abstract for Dendroica kirtlandii (Kirtland’s warbler). Michigan Natural Features Inventory, Lansing, MI. 5 pp.
• Ortega, C. P., J. F. Chace, and B. D. Peer. Eds. 2005. Management of cowbirds and their hosts: Balancing science, ethics, and mandates Ornithological Monographs No. 57. American Ornithologists’ Union. These papers were of particular interest:
  • Ortega, C. P., A. Cruz, and M. E. Mermoz. 2005. Issues and controversies of cowbird (Molothrus spp.) management. Pp. 6-15.
  • Kus, B. E. and M. J. Whitfield. 2005. Parasitism, productivity, and population growth: Response of Least Bell’s Vireos (Vireo bellii pusillus) and Southwestern Willow Flycatchers (Empidonax traillii extimus) to cowbird (Molothrus spp.) control. Pp. 16-27.
  • Chace, J. F., C. Farmer, R. Winfree, D. R. Curson, W. E. Jensen, C. B. Goguen, and S. K. Robinson. 2005. Cowbird (Molothrus spp.) ecology: A review of factors influencing distribution and abundance of cowbirds across spatial scales. Pp. 45-70.
  • Peer, B. D., S. I. Rothstein, M. J. Kuehn, and R. C. Fleischer. 2005. Host defenses against cowbird (Molothrus spp.) parasitism: implications for cowbird management. Pp. 84-97.
  • Rothstein, S. I. and B. D. Peer. 2005. Conservation solutions for threatened and endangered cowbird (Molothrus spp.) hosts: Separating fact from fiction. Pp. 98-114.
• Ortega, C. 1998. Cowbirds and Other Brood Parasites. University of Arizona Press.
• Siegle, R. and D. Ahlers. 2004. Brown-headed Cowbird Management Techniques Manual. U.S. Dept. Interior, Bureau of Reclamation Tech. Serv. Center, Ecological Planning and Assessment Group, Denver.

(Previous posts in this series: Introduction, Cowbirds 101, Responses to comments on Cowbirds 101, Problems with Cowbird Control)

I originally intended on making this the last post in this series, but I have been talking to some sources in the Kirtland’s Warbler management and research world, and I’d like to incorporate what I’ve learned into my finale. This just ended up getting way too long. I promise to wrap it up…in my next post. Here I will introduce Michigan’s most famous bird, the endangered Kirtland’s Warbler.

Kirtland’s Warbler background

Kirtland’s Warbler is an historically rare bird with very specific nesting requirements: it will only nest in Jack Pines (Pinus banksiana) that are 6 to 24 years old. And Jack Pines require fire to clear land, enrich poor local soils, and to open their cones and release the seedss Further, because the warblers nest on the ground, they nest successfully mostly in Jack Pines growing on a certain type of quick-draining soil known as Grayling sand. This is why the range of this warbler is restricted to the southernmost portion of the range of Jack Pine, found primarily in northern Lower Michigan. Thus, breeding habitat is rare and ephemeral.

Harold Mayfield, an ornithologist and driving force of early Kirtland’s Warbler conservation, wrote in his Birds of North America account of the species that they “probably survived near extinction for many centuries” due to their specialized habitat requirement. The warblers may have reached their peak abundance in the late 1800s and early 1900s, aided by the regeneration of forests that were intensively cut during the peak of Michigan’s logging era (1870-1900), and the dramatic forest fires that burned millions of acres during that period. Concurrently, it is estimated that cowbirds arrived in Michigan about 1850, and by the time of the publication of Michigan’s first detailed bird list, in 1912, they were considered abundant across the state, their spread also facilitated by the changing landscape forged by humans.

Over the last century, logging, forest fragmentation, and fire suppression reduced this already rare habitat. By the mid-1950s, the nesting range of Kirtland’s Warbler was a few counties in the northern Lower Peninsula of Michigan. The first census of Kirtland’s Warblers counted 432 singing males in 1951. In 1961, the count was 502. In 1967, Kirtland’s Warbler was one of the first species to be listed as federally endangered. Annual surveys began in 1971, when 201 singing male Kirtland’s Warblers were counted. At that time cowbirds parasitized about 70% of warbler nests.

Cowbird control was initiated the following year. Within a decade, the parasitism rate declined to under 4%. However, from the onset of cowbird control in 1972, for another ten years beyond the precipitous drop in the cowbird parasitism rate, the population of Kirtland’s Warblers remained about the same (click on graph).

Warbler populations began to take off when a huge chunk of habitat became available to them. In 1980, a prescribed burn in the Mack Lake area went out of control. Recall that Jack Pines are fire-dependent, and warblers prefer Jack Pines that are a minimum of six years old, or about 2 meters tall. When the Mack Lake burn habitat was optimal, around 1990, the warblers moved in, and populations took off. In 1991, 60% of all singing male warblers were in the Mack Lake burn.

The Mack Lake burn habitat is now becoming too old for the warblera. Fortunately, Jack Pines have been planted over the years, providing new habitat. In 2005, the annual census counted 1,451 singing male Kirtland’s Warblers. From the original six-county core range in Michigan, they were located this year in eleven Lower Peninsula counties and five counties in the Upper Peninsula. Males have also been found in Wisconsin and Ontario.

My wrap up will touch on the role of cowbird control in warbler recovery, what is next for the program, and some concluding thoughts.

Many thanks to Bryan Pfeiffer at Wings Photography for use of his stunning Kirtland’s Warbler photo.