Friday, September 08, 2006

Blakeman: the end of a delightful exchange

Red Squirrel in Central Park - January, 2006
Photo by Bruce Yolton

This is really the last of the redtail-vole debate:


I appreciate Chris Lyons’ more detailed elucidation of the 19th century Pennsylvania “Scalp Law” episode, a most important (and tragic) legislative experiment in ecological manipulation. Then, as now, nature isn't always as well-understood or controlled as imagined by those who have the power to create laws and regulations.

I also appreciate and concur with Chris’ views that raptors should be protected because they exist and are natural, not because they might provide some putatively useful ecological service.

Chris makes a broad case for the cumulative roles that all predators play in slowing or rounding off periodic vole population hikes. I don't believe that I suggested that all predation of voles, such as that by weasels, minks, foxes, and snakes (the most common consumers of voles), fail to have any impact. They do. But I specifically contended that red-tailed hawks have virtually no impact, that we shouldn't be claiming that red-tails are essential or important rodent-control agents. Red-tails simply can't eat enough voles each day in their large, multi-square mile hawk territories. . .

But what about squirrels, especially those that declined near a red-tailed hawk’s nest at Fordham University? That’s different. Squirrels don't breed as often as voles, with only one or two litters or so each year, and their populations aren't so large, either. A squirrel makes a nice day’s meal for a red-tail, so it could take seven in a week. A pair could take a over a dozen each week. That could be forty or so in a month. In a small area such as college campus, a pair of red-tails could markedly depress a squirrel population.

And as a falconer who has seen red-tails pursue squirrels up close, I know that squirrels are actually rather easy prey for our big hawks. If the squirrels stay up in the trees, they are relatively safe, able to scoot around a trunk or branch, or duck into thick branches that the hawk can't fly through. In the trees, squirrels are difficult for red-tails to capture. It requires a lot of vertical flying, causing the hawk to quickly ascend into the limbs of the trees. This uses a great deal of energy and unless the squirrel makes an unfortunate mistake, the hawk usually gains nothing for its efforts.

But when a squirrel walks out onto open turf, as found in parks and campuses, the hawk has every advantage. A squirrel out in the lawn is a relatively easy target for a red-tail. It can stoop, or dive, from a nearby tree or building and swoop across the lawn at 60 to 80 MPH. The little squirrel can't run nearly as fast, and may not even see the hawk until too late. From what Chris described, I'm certain that the Fordham red-tails have made a real dent in the local squirrel population. Surely, they can capture and eat those arboreal rodents faster than they can reproduce.

Perhaps there are still as many Fordham squirrels as before, but they may have learned to remain up in the trees, staying off the ground where they are easily pounced upon by the local hawks.

<>And for me, this, too, should be the end of this delightful exchange of thoughts and perspectives on the roles of hawk predation on vole populations. These have been wonderfully thought-provoking concepts and reports...

John Blakeman

[PS from MW]: I've added a source for a quote to the previous post by Chris Lyons. the one John Blakeman is responding to here]

Back to voles -- Lyons responds to Blakeman

Pale Male with rodent prey -Metropolitan Museum -8/6/06
Photo by Bruce Yolton

The final salvo in the vole debate--by Chris Lyons
[This is in response to John Blakeman's post on 9/02/06] :

After John Blakeman's last response on this subject, I figured I'd better do some more careful research, to see if in fact there was a strong scientific consensus on the question of what role (if any) predation plays in the life cycles of rodents, particularly voles--the answer seems to be that biologists have held a variety of opinions on the matter of vole populations, and what makes them periodically rise and fall. There certainly was a strong current of opinion in the latter half of the 20th century that microtine (vole and lemming) populations are self-regulating, and primarily affected by overpopulation pressures, disease, available food, etc--and there is no doubt all those factors are of tremendous importance. At one point, the pure cyclical explanations do seem to have been dominant over theories involving wild predators. But scientific opinions on the role of predation in rodent populations have themselves experienced a certain cyclic ebb and flow, and there have been a large number of recent studies that indicate predators may play a very important role in regulating voles, and other prolific potential pests (all of which have their place in nature, of course).

As microtus populations increase, their predators likewise can breed more abundantly, and more mobile predators will seek out especially large concentrations in winter, when territoriality is not an issue. Any serious local birder knows there are fields a short drive from New York City where multiple species of owls and hawks can be seen in amazing numbers in winter, all of them hunting small rodents--and then drifting away to other hunting grounds as prey numbers become too low to sustain them. A rodent 'hot-spot' is quickly identified and exploited by birds of prey during the fall and winter months.

Some predators that don't normally specialize in microtus will feed heavily on them as their numbers climb, including coyotes, wolves, and even bears. Everybody joins in the feast. Many scientists believe that the cumulative impact of this steadily increasing multi-predator onslaught does, in fact, seriously diminish vole and lemming populations at certain points in their population cycles--perhaps only hastening their natural cyclic decline to a greater or lesser extent. Others believe predators have more of an effect in terms of slowing the upswing of vole populations. Overall, there is a substantial body of opinion that even if microtine populations would fluctuate with or without predators, predation does limit the severity of their regular rises and falls--it both preserves and controls natural cyclicity. There is speculation that one reason for voles and lemmings having evolved in such a way as to guarantee regular crashes in their numbers may be to discourage more predators from becoming specialized to hunt them. Whether by design or not, their population cycles also have the effect of temporarily decreasing the numbers of their most dangerous enemies. It's well known that when lemming populations crash, the populations of those lemming-hunters who can't readily switch to other prey crash along with them--these crashes frequently trigger mass southward irruptions of birds of prey such as Snowy Owls, most of whom probably do not survive their exile. The Red-Tailed Hawk is too much of a generalist to be critically affected by sharp declines in the numbers of one of its prey animals. Others are not so fortunate.

Getting back to the issue of the Pennsylvania "Scalp Law" of 1895, I found primary sources hard to come by, but I did manage to learn a bit more. The law was enacted to encourage the shooting and trapping of all predators perceived to be threats to livestock (primarily poultry, since large predators were nearly eradicated in Pennsylvania by this time). "For the benefit of agriculture and the protection of game", it attached a price of 50 cents per scalp for ANY bird of prey other than the "Acadian" (Saw-Whet), Screech, and Barn Owl. It also included "Wild Cats, Foxes, Minks, and Weasels." With 50 cents being a significant sum of money at the time, the law created a powerful added incentive to hunt down animals that were already being ruthlessly destroyed by man--most of which were important rodent predators; most particularly the weasels, voracious animals, well-adapted to 'ferret out' and slaughter rodents in their own burrows, known to sometimes kill more individuals than they can eat--and which have been observed to prey with particular success on female voles with young.

It also put a big drain on the public coffers, and created a lot of work for the government officals administering it, which quickly made it unpopular with them. Proto-environmentalists of the time were vocal in their criticism of the "Fool Hawk Law" (while still insisting that it was perfectly all right to kill any accipiter you saw). However, raids on chicken yards did apparently decrease, and the law might have remained on the books a lot longer than it did, had Pennsylvania farmers not begun to report a great increase in agricultural pests, primarily rodents--no specific information on what species of rodents, or what crops were most affected, or in what areas--there were dollar-estimates put out as to how much the law saved agriculture in terms of chickens, as opposed to how much it lost in terms of damage caused by vermin, but these were educated guesses at best. Probably a great deal of the destruction was caused by rats (the imported variety), which as John Blakeman has many times pointed out, are ideal Red-Tail food. While fast breeders, rats are less staggeringly prolific than voles, and are usually found in the immediate vicinity of human habitations--where no hawk in a non-suicidal frame of mind would have been found in 1896.

Could populations of rats and other medium-sized rodents have been regulated by raptors, including Red-Tails? I'll leave that question to the scientists, but I can relate a personal observation. In the short time since Hawkeye and Rose, the Fordham Red-Tails, took up residence at the Rose Hill campus, everyone here has noted a substantial drop in the numbers of squirrels. Only a few years ago, you couldn't leave the library at certain times of the year without seeing 30-40 squirrels foraging on the lawn outside--and their numbers on the campus as a whole were extremely dense, and somewhat isolated from surrounding areas, due to the campus being entirely surrounded by wide roads with heavy traffic. Though likable animals, who add much to the atmosphere of the campus, the squirrels were so numerous and bold as to frighten some people--they startled me more than once. While watching the hawk nest, I've had quite a few people mention to me that they are seeing a lot fewer squirrels around. This may be partly because the squirrels are being more careful about exposing themselves to potential predation, but I still see them out in the open--just not nearly as many. The change has been remarkably rapid and obvious. And squirrels, of course, are far harder for Red-Tails to catch and kill than rats. So if one breeding pair of Red-Tails, not feeding exclusively on squirrels, could have this great an effect in so short a time on so challenging a quarry, it's not hard to imagine that removing nearly all potential rat predators from a farming area could have the opposite effect.

Back to 1896--if voles did increase during this time, it is hard to believe that farmers who had spent their whole lives dealing with rodent pests would not have been able to recognize a perfectly normal 4-5 year upswing in vole numbers (however they explained it). So whatever did happen in this period, presumably it was something both immediately noticeable and out of the ordinary--and rather glaringly coincident with the dramatically increased slaughter of vole predators. It would be nice to know more, but there just isn't enough available data to definitively support any particular point of view on the cause of this phenomenon.

What we do know is that the 1895 bounty law was repealed in 1897, but persecution of most of these wild hunters continued for many subsequent decades, albeit with an increasing attempt to spare those deemed useful to man (so long as they weren't seen to be overly interested in his chickens). To argue that reports of increased rodent problems were inspired by emotion-driven conservationist fantasies is to ignore the fact that none of these creatures was viewed sentimentally at the time by the great majority of the population--they were almost universally reviled as murdering thieves and worthless vermin.

The passage of the Scalp Law was viewed positively by around 90% of Pennsylvanians, until its less fortunate consequences became apparent. No 19th century farmer was going to change his mind about these bloodthirsty chicken-stealing varmints. He might, however, come to realize that he was paying a higher price for their extermination, in both cash and crops, than the loss of a few chickens warranted. The decision to repeal the bounty was strictly a matter of dollars and sense.

Interestingly, a similar situation occurred in Scandinavia, not long after the Pennsylvania bounty was repealed--.

"In the beginning of last century a massive countrywide predator extermination program was started in Norway. The government of Norway paid a bounty to hunters for all medium-sized mammalian predators, owls and raptors. Bounty program and propaganda against all predators led to a large-scale reduction in the numbers of these predators. Steen et al. (1990) reported the apparent consequences of this 'unplanned experiment' influencing small mammal populations. They observed loss of cyclicity for approximately 20 years, in addition to the loss of large-scale regional synchrony in voles and lemmings "
[ Source:
Vole Population dynamics: experiments on predation
Janne Sundell, Academic Dissertation, May 2002.
University of Helsinki, Faculty of Science, Department of Ecology and Systematics, Division of Population Biology .]

If I have made this subject sound overly complex and involved, believe me, I've actually oversimplified it quite a lot--for my own sake as much as the reader's. I realize this discussion has strayed pretty far afield of its origins (somebody found a dead vole in his backyard, killed by a species of hawk that isn't even supposed to be preying on voles). Perhaps the most important thing is that we all agree that birds of prey are worthy of survival, that they enhance our lives, and that their lives are valuable in their own right, not merely as ornaments to our skies, or as unpaid pest-controllers.

I remain convinced that raptors, and many other predators play a vital role in regulating the populations of their prey, often to the benefit of man, although many other regulating factors exist. Whatever the facts may be, they must be determined by scientific inquiry and analysis. Since the scientific community is notorious for taking a long time to make its mind up, I'm not holding my breath for its final answer.

Thursday, September 07, 2006

At the Wildflower Meadow

This remarkable photo of a Viceroy butterfly caught in the act of depositing an egg on a plant at the Wildflower Meadow [North Woods], was taken by James O'Brien

A few facts from the Internet about Viceroys:

The Viceroy Butterfly is a black-and-orange insect that closely resembles the Monarch.
The viceroy and monarch were once thought to exhibit Batesian mimicry where a harmless species mimics a toxic species. Studies conducted in the early 1990's suggest that the viceroy and the monarch are actually examples of Mullerian mimicry where two equally toxic species mimic each other to the benefit of each. It can be distinguished from the Monarch by the black line that crosses its wings. Also, the undersides of its wings are quite similar to the topside (unlike the Monarch, whose underside is much lighter).

The Viceroy is a strong flier; it has a wingspan of 2.75 to 3 inches (7 to 7.5 cm). It has a black, fuzzy body.

The Viceroy is found from Canada to Mexico. It inhabits riverbeds, wet meadows, marshes, and other wetlands where willow, poplar and aspen trees occur. This species is in danger of extinction due to loss of habitat.

The caterpillar is olive green and brown with bristly tufts behind the head (the caterpillar resembles bird droppings) . It eats mostly willow and cottonwood.

Classification: Order Lepidoptera (butterflies and moths), Family Nymphalidae (brush-footed butterflies), Genus Limenitis, Species archippus.

Tuesday, September 05, 2006

Moth Tree Roundup

What is the moth tree? A quick repeat for new readers:

There's a scraggly English Oak just off the park's East Drive, between the Boathouse and the 72nd Street transverse, that oozes a pungent sap from various places on its bark. This sap, as it happens, is highly attractive to certain insects both day and night.

In the daytime, depending on the season, you'll find Bald-faced Hornets, Cicada-killer Wasps, Question-mark and Comma butterflies and some diurnal moths such as The Nessus Sphinx, slurping up the sap. After sunset the Underwing family of Moths, officially known as the Catocalas, arrive, among the most dramatic of our northeast moths. We have seen more than 20 species of Underwings at this single tree. [Last year we also had a historic visit from a Black Witch, the largest moth in North America.]

A small group of moth enthusiasts gather at the Moth Tree every night, armed with flashlights and the one existing moth field guide,[Covell] to enjoy the beauties of these dramatic creatures and to try to identify them.

Here are some recent visitors, Underwings and others:

Oldwife Underwing

The Darling Underwing - 9/3/06

Greater Black-letter Dart 8/31/06

Yellow-striped Armyworm Moth 8/31/06

Once-married Underwing- 9/1/06

All photos by M. Winn, taken with a Canon Powershot S 410, Digital Elph on a macro setting.

Monday, September 04, 2006

More Joy of Insects: Flies

Flies --order Diptera, easily distinguishable from other insects because they have only one pair of wings. There are about 16,300 known species of fly in North America.
Note here, in Lloyd Spitalnik's photographs, the large compound eyes. This is a feature of the Dipteran order.

Robber Fly

Fruit Fly

Syrphid Fly

Another Syrphid Fly

Tachinid Fly

taken on 8/20/06 at Turtle Pond

Sunday, September 03, 2006

Pale Male & Lola news

Lincoln reports that after several weeks of absence from the nest, Pale Male & Lola spent several hours fixing up and straightening twigs in the nest yesterday 9/2/06. Maybe the New York Post, after its many reports and headlines announcing that the famous pair has moved to the Beresford on the West Side, will print a retraction.

Photo by Lincoln Karim

The joy of insects--Part I

The first installment of a treasure-trove of photographs taken by LLOYD SPITALNIK

Below are 4 WASPS and 1 pair of X-rated BUGS. All insects were photographed at Turtle Pond on 8/ 20/06..

Potter Wasp

Weevil Wasp

Scoliid Wasp

Great Black Wasp

Mating Milkweed Bugs