Migration

Our experience this year suggests there may not be a hawk migration at Harvey's Knob, but rather a random occurrence of hawks. In fact, thinking back, very few hawks actually use the ridge - most are crossing. Broadwings seem to use the ridge late in the evening when they are trying to get the last possible southward movement - otherwise they occur randomly all over the place. Redtails use the ridge in November when there are strong NW winds only - otherwise they are hunting or crossing. The most consistent hawks on the ridge are Ospreys in the Spring on SE winds.

bj

It is my experience that all hawkwatching sites are experiencing a random occurance of migrating hawks both in the spring and the fall. A hawkwatching site with a purview of two to three miles cannot claim to be a site that is collecting data for a final determination of the whys and wherefores of hawk migration. Such a site is merely gathering data for appeasing those at that site in competition with those at another site. Ha Ha, we saw more than you!

The topography and weather ,on any given day, of the site within the two to three mile purview absolutely dictates what the hawkwatcher will see on any given day. If the weather is static the hawks will be moving on solar induced thermals and if the territory within the two to three mile purview of the site is not conducive to solar induced thermals then few migrating hawks will be seen. If the weather is dynamic such as after a cold front passage the weather within the two to three mile purview will be strong northwest winds. Such winds will produce a ridge lift soaring condition on which the migrating hawks will congregate.

Migrating hawks will only congregate in areas that are conducive to soaring flight. If your site is lacking of the terrain that produces thermals then your site is lacking in the count of hawks. If your site is level withot a bump in ita course then ridge lift flying hawks will not congregate. But, each of these condintions will exist at any site. And they will produce3 a congregation of migrating hawks. The only questio0n is: How much of a congregation?

Hawk Migration Spring and Fall

Apr 30, 2008

Hawkwatchers everywhere should realize that their purview consists entirely of examining, primarily with the naked eye, a two to three mile patch of sky. Considering that there are less than one hundred consistently manned hawkwatching sites on the North American Continent this examination of the hawk migration is pathetically small. It is minuscule to the point of being laughable insofar as any studies of hawk migration with a desire for an accurate monitor of hawk populations is concerned.

We all flock to the lookouts in the Fall of the year to witness a sample of the breeding populations that are heading to a territory that is more conducive to the survival of those breeding hawks. And, we all dutifully record those numbers of southbound migrants with the thought in mind that we are indeed making a contribution to the preservation of the environment of migrating hawks and in a larger sense the ecology of the vertebrates of the earth including ourselves.

Excuse me if I am more convinced that we are only concerned with having a good time on watch and that we are collecting our numbers for the simple reason that we are highly competitive with those who dared to attend a lookout different from ours. Well every game, sandlot or not, needs a referee and a record.

It is the two mile purview that bothers me as that narrow view is severely lacking for the Fall migration. But, to completely ignore the Spring migration just blows my mind. If one is truly interested in hawk migration he should be willing to move about in the fall in order to intercept more migrants than the the nearest site. If one is truly interested in hawk migration one must participate in a hawkwatch during the spring. There is no reason to believe that every hawk on each day in the fall will pass by the selected site and there is no reason to believe that the breeding hawks will return by that selected site in the spring.

For those who are truly interested there is a great menu of selections for you to consider in order to truly contribute valuable data to the hawkwatching record. Take the Candler's Mountain record and the weather conditions that produced the flights there and compare them with what was found at Harvey's Knob. That should provide a clue to where the hawks are flying on their southbound journey.

Consider the spring migration movement. For some thirty years it has been considered at Harvey's Knob that the spring migration produced lower counts because of the mortality rate during the fall migration. Such a notion was based, in part, on the fact that the Hawk Mountain counts were extremely lower in the spring than in the fall. Permit me to submit one question: Where is it written that the migration is symmetrical? Those of us in the southeast know to concentrate our hawkwatches on NW winds in the fall. And, we found early, that NW winds produce no hawks in the spring. Our solution to this pattern was to abandon spring watches.

During the spring migration the multitude of breeding hawks that wintered in the tropics are indeed migrating symmetrically through Central America. They are exploding out of Mexico in late March and early April. They are drifting around northward in the southern and central plains. Then a cold front passes through that territory and spawns northwest winds across that territory. Those winds blow across the western front of the Appalachian Mountains. Playing those winds (there is no such thing as a wind blown hawk) the northbound migrants gather along the western slopes of the Appalachians in Tennessee, Kentucky, and West Virginia. There are two mountains in this purview that reach into Virginia: Pine Mountain on the border of Virginia and Kentucky that hosts the Breaks Interstate Park and Clinch Mountain a bit eastward hosting a VDGIF Wildlife Management Area. As a last resort for spring migration on NW winds there is Peter's Mountain near Bluefield, WVA.

It is obvious that hawkwatchers need to expand their scope if they are truly interested in learning the behavior of the hawks during migration. The above suggestions will go a long way toward such a conclusion.

Yes Virginia there is a viable spring hawkwatch.

Dave Holt

Broadwings 2007 at Selected Sites

(Click on the chart)






















































































I can’t do anything with the surface maps as there is too much info and I cannot get oriented.

But the tabular info is very interesting as it shows a high flight of Broadwings thru northern New Jersey where it is hard to distinguish a ridge from normal low level terrain. The flight at Scott Mt., New Jersey clearly indicates a flight that may or may not follow ridges but proceed down thru the Piedmont areas of the mid-Atlantic states, and it was a huge flight. The fact that the Hawk Mt., count was only very slightly increased and that Waggoner’s Gap and Hanging Rock did not show substantial increases indicates to me that the bulk of the Bws did soar down the Piedmont and not along the ridges.

We definitely need more data from Piedmont sites. I wonder if the Militia Hill site in Philadelphia reported in 2007. It is a pity that there are no sites situated in the Piedmont of Virginia as such a site or sites could provide a great deal of information about the behavior of Broad-winged hawks in migration.

In support of the Scott Mt. site in NJ I also wonder if the Montclair, NJ site is still reporting.

You see, we have a cluster of sites in the NE or northern tier of the U.S. but coverage is sparse to non-existent east of the Appalachian Mountains in the south starting at the Maryland State line.

I mention all this because we at the Harvey’s Knob site are always wondering where our hawks come from. We can assume almost any direction but we cannot offer a plausible explanation for any direction. A large bulk of hawks moving down through the Piedmont of Virginia that encounters several days of easterly winds may indeed show up at the Harvey’s Knob site in extraordinary numbers. That is precisely what we are beginning to surmise about the extraordinary flight of 2007. But we have absolutely no supporting data from Piedmont sites in our own state.

If there are any folks from around Richmond or Farmville or wherever who wish to go hawkwatching without the long drive to Rockfish or Snickers, may I suggest that you find a place close to home with a near 360 degree view of the sky and sit it out for a few days next fall. It isn’t written anywhere that a mountain is necessary for a hawkwatch. Ask the folks at Detroit, MI, and Windsor, Ont., and they will refer you to years of outstanding counts in some of the flattest country I have ever seen.

Excuse me for proselytizing, but in light of the fall 2007 counts at Harvey’s and Rockfish the need for Piedmont hawkwatches in Virginia has once again raised its ugly head. That is if we are ever to fully understand the behavior of hawks in migration.

Dave Holt
12/19/07











dh

Weather Data of September 18, 2007

I trust Dr. Holt will comment on these data relative to weather and the Broadwing flight of that September 18, 2007.

If you click on any of these graphs, they enlarge into the visible range.

Here are data from Buchanan for the month of September, 2007:



Here is the graph from Buchanan for 9/18/07:



Here is Lynchburg for the same day:


And Hollins:

Finally, Blacksburg:



Here is the count for 9/18/07 with weather mountain observations:


I continue my search for a representation of the weather that may explain flight. To that end, below are other graphs for that day which I trust Dr. Holt will comment on below (or possibly delete).

Roanoke airport:
This is "Frontal Positions":



Surface Pressure:



Frontal Pressure Tendency:


Surface wind:



Surface relative humidity:




Sorry about the graphics.

Dr. Holt responds:

I am overwhelmed as I am one who prefers to reduce the complex to its simplest terms and then build the theory from those simple terms incorporating the complexities into the complex whole the theory may entail.

Having said that, I am convinced that most people reading the above answer will be convinced that I am full of...

I am doing my own research of some data that I have selected and I will try to incorporate the data that Bill James has unexhaustively extracted from the web. But it will take awhile.

Meanwhile permit me to offer my theory of migration and how it coincides with the latest findings at the Harvey's Knob site.

I believe that because the migrating hawks especially the migrating buteos are driven to seek the means of soaring flight that the means of soaring flight are the prime determination of their behavior during migration.

There are two meteorological/topographical events that will provide the means for soaring flight. They are solar induced thermals and ridge lift. As the migrants move south they are constantly seeking either of these two means of soaring flight.

Since the solar induced thermal is the primary means of soaring flight the southbound hawk is usually moving southward via the solar induced thermal. If the southbound hawk does encounter mountainous terrain and ridge crossing winds then the hawk will elect to continue its southbound journey via the ridge lift means of soaring flight.

Mountain ridges are not leading lines for the migrating buteo unless the ridges are under the influence of ridge crossing winds. When the winds cross ridges and the ridges are aligned NE to SW then the ridge lift condition exists and the southbound buteos will be seen along the ridges. But, we must remember that the solar induced thermal condition is the rule while the ridge lift condition is the exception to the rule.

Taking that last fact into consideration requires that we consider that the migrating buteos are meandering southward on thermals most of the time. When strong winds occur in a ridge crossing direction on the few occasions they occur, the migrants will then gravitate to the ridges. They will remain in the vicinity of the ridges as long as those ridge crossing winds occur with any degree of consistency.

Therefore it is not only important to know what the weather conditions were on the day when the big flight took place it is important to know what the weather conditions were for several days before the big flight occurred.

We all know that westerly winds at the Harvey's Knob site will produce large flights but do we know what weather preceding the day of the big flight will produce an even larger flight?

Dave Holt

December 7, 2007 9:19:00 PM EST

BJ adds:

I may be wrong in trying to analyze the day of the big flight as opposed to equal scrutiny for preceding days. However, my thinking is that the Broadwings go by Harvey's Knob every year and the question is whether we can see them or not. When we do see them, it seems it is likely related to the conditions on that day. To some extent, we can research a lot of those days and, of course, we have even more data characterizing when they do not come into view. The difference between seeing them and not seeing them is certainly related to the weather and should be quantifiable. I am looking for variables that will help us quantify the 'ideal' day and I don't believe we have that model yet. To me, the biggest problem with studying hawk migration relative to weather is that you do not know how many hawks are out there. In that small window in mid-September, we know they are out there in big numbers and can use that time to effectively study hawk flight and atmospheric conditions.

I also wonder if there are not more possibilities for flight strategies. Couldn't hawks use thermals that are present on the mountain as well as in the valley? Can't they fly in a good wind through the valley without using the mountain?

If we could create the perfect day for hawk flight by Harvey's Knob, what would characterize that day?

Dr. Holt responds:


Bill and I are in total agreement about the migration in the vicinity of the Harvey’s Knob site. In my opinion the BWs are constantly moving through the latitude of the HK site during the last two weeks of September. Whether they are seen at HK site is indeed a matter of the weather conditions that occur while the watch is manned.

We must remember that we are only sampling a two mile patch of sky. A BW seen by the naked eye must be at most 3/4 of a mile away. Most of the BWs seen at the HK site are less than 3/4 mile away even those dots high overhead. Why are they in view in the first place is the question Bill and I are striving to answer.

As I mentioned above the birds are soaring on thermals during most of their migration period.
But, the heavily forested slopes of the Blue Ridge are not conducive to thermal soaring. The sun does not directly strike the western slope of the Blue Ridge during the third week of September and after the autumnal equinox it does not strike the western slope in the vicinity of the HK site at all. That leaves the crest of the ridge to be exposed to direct sunlight between the hours of 10:00 AM and 2:00 PM. The asphalt of the BRP, overlooks, and various openings and rock outcrops. A brief survey of the valley on each side of the HK site reveals a terrain rich in thermal activity. These thermal soaring possibilities on the mountain will produce large numbers of migrating Broad-winged hawks. Numbers that will continue excite the veteran hawkwatcher.

But, the average number of migrating Bws at the HK site is between 6 and 7 thousand. On 18 Sept, 2007 this number was exceeded in a single day. Also on a day during the third week of September in 1996, 5000 hawks were recorded. These are extraordinary numbers and there must be an explanation for their occasional appearance at the HK site. This is what I am interested in finding out and where Bill and I part ways a bit.

I am convinced that a continuation of ridge crossing winds for several days before the extraordinary day will influence the thermal soaring hawks out in the valley to gravitate to the ridge in numbers that when the proper conditions occur at the HK site an extraordinary single day count will occur. It doesn’t happen often and for that reason that is what I am after. I simply want to explain the extraordinary as I believe the normal may already be known.

Consider the following scenario: The bulk of the migrating BWs are migrating southward via the near constant thermal soaring condition. However the thermal density is such that fewer thermals occur within a purview of two miles at the HK site. Thermal density beyond that purview is greater therefore many thermal soaring migrants escape detection from the HK site.

What will bring the soaring migrants into view is a stiff ridge crossing wind. When such a wind occurs the thermals are shut down at ground level and ridge lift soaring becomes the dominate means of soaring. A wind speed gradient that always occurs may produce light winds at the valley floor and allow thermals to take place but they will not achieve much altitude before being blown away downwind. However, a thermal tilted by the wind toward the mountain will put even more migrants in view.

I am convinced that extraordinary days in the Broad-winged hawk migration season at the Harvey’s Knob site is due to ridge crossing winds either on the day in question or for a few days before the day in question. The data that Bill James has presented above offers absolutely no evidence to support my conclusion. I shall now invoke that overused phrase so often heard in the soft science circles; More work is needed.

Dave Holt
Dec. 8, 2007

BJ:

I am ready for more work. Perhaps my research into weather conditions on that day is premature. I am assuming there are a lot of BWs around during this period in September, likely thermaling through the valleys on both sides of us or riding the ridges to the North, and that they come into our view when conditions on a specific day are conducive to movement in our direction. If I understand your hypothesis, you suggest that a necessary ingredient for their appearance in numbers is a series of days where conditions bring them closer to the ridges and, more specifically, ridge crossing winds of substance. This appears to be testable.

But where do we look for that data for the test? We don't look at Harvey's since in the days before the big flight, they are not there. We would have to look to the North. Should I look for ridge crossing winds at Rockfish and Snickers in the week before our big flight? Or should I look for the passage of low pressure systems in the mid-Atlantic during that period? If I do, what would you suspect I will find?

12/9/07

Thanks for your suggestion to click on the graphs to enlarge them. I thought this method was only used on porn sites. Anyway, after review I find that there are no conclusions about the weather conditions for the month of September 2007 that can point to why the extraordinary flight of 18 Sept. Certainly the winds immediately preceding that day were not conducive to bringing Great Valley bound hawks to the Blue Ridge. They may have been conducive to bringing Piedmont bound hawks to the east to the Blue Ridge but that is a stretch.

Before we get into a discussion of wind blown hawks let me say emphatically that there is no such a thing as a wind blown hawk. Hawks are a flying object that has nearly zero drag. They are not wind blown. If they were those massive migrations in the Detroit area would be blown into the Atlantic Ocean when caught by the NW winds following a cold front passage. It is my belief that those hawks migrating in or near mountainous country sense the winds when they rise from their perch in the AM. If the winds are of a direction to cause ridge crossing winds the hawks will look to and gravitate toward the highest object in their purview.

The absence of ridge crossing winds of a consistency and strength during the days preceding the extraordinary flight of 18 Sept., lead me to believe that my theory above is completely wrong. And you and I have long since agreed that the hawks seen on 18 Sept., were strictly soaring on thermals. While I can account for the good viewing conditions on 18 Sept., I cannot account for the exceptional numbers of that day.

My theories have all been derived from my experience at the WRNC site during the Red-tailed hawk migration season. At that point close to the valley, when the hawks were soaring on thermals we would see them rise and catch a thermal and soar SW without moving toward the Blue Ridge. But if the winds were strong NW we would see them rise and immediately move toward the Blue Ridge to soar SW on ridge lift.

I recap that experience because I am coming to the conclusion that it is grounded in a very narrow view. Perhaps, an examination of the more northerly lookouts and their wind conditions are the next step. So if the boss (Bill James) is eager to work I would say go to the Rockfish Gap site and if possible to the Candlers Mt., site to look for something that put an extraordinary number of Broad-winged hawks in the vicinity of the Harvey’s Knob site on 18 Sept, 2007.

Dave Holt
12/10/07

Great Observation 2 Nov 2007

On 2 Nov. 2007, Bill James found at the Harvey’s Knob (HK) site that the Red-tailed hawks weren’t flying past the site during the morning hours while he was experiencing westerly winds at a velocity that should have provided the Red-tails with a ridge lift soaring opportunity.

He did find a substantial number of Red-tails after the noon hour and he wondered at this apparent contradiction in what we have come to believe is the motivation for Red-tails to pass the HK site. Bill did a little research, checking with two weather stations at lower altitudes and found that the lower altitudes did not experience the wind velocity that the higher altitudes did during the morning hours. Therefore the Red-tails that were perched on the valley floor the night before did not experience winds strong enough to influence them to seek out the ridge lift condition when they awoke that morning.

They sought and probably found a few thermals suited for soaring flight during the morning hours. These thermals were tilted by westerly winds toward the crest of the Blue Ridge where Bill was diligently perched. But the strong winds began to dissolve the thermals and left the Red-tails to seek out and find the ridge lift opportunity for soaring flight that they missed when they left the perch. It was at this time that Bill was able to start his count.

In my years of hawkwatching during the Red-tailed hawk migration season I have found the same characteristics at the HK site. No flight during the AM hours but a reasonable though not sensational flight in the PM hours. Wind velocity was the same all day. I have also watched the Red-tails migrate from a valley site at the Woodpecker Ridge Nature Center (WRNC) site.
Lo and behold at the WRNC site there is always a flight in the early morning hours.

When the winds are moderate on the mountain they are light in the valley. Light winds will not cancel thermal activity but strong winds will. Therefore in the morning hours when the winds are moderate to strong on the mountain and light in the valley the migrating Red-tails will choose thermals for there desired soaring flight southward. But when the Red-tails reach the top of the thermals they will find that the thermals are not only tilted toward the mountain when the winds are westerly the thermals will loose their strength for upward flight. The Red-tails will then gravitate toward the mountain. Quite a few will continue to proceed southward via thermals which are by their nature displaced too far from the mountain for good viewing from the mountain.

What Bill found on 2 Nov, 2007 is that the wind velocity varies and that where the birds perched the night before also varies. The Red-tails moving north to south the day before may not have perched on the mountain for the night. The next morning when they awoke the Red-tails sought some indication for where their opportunity for soaring flight would occur. Ordinarily one would assume that a westward wind sweeping across their bodies would have influenced them to seek ridge lift. But, if the winds at their perch were light they would seek their old standby: the solar induced thermal.

Thermal soaring Red-tails at the HK site are very difficult to find as thermals do not occur very close to the site. But ridge lift soaring opportunities will bring the hawks very close to the site.
If the hawks are flying far from the site on thermals in the morning and close to the site in the afternoon, the day on watch can be well described as a differential in wind speed between the AM and PM hours.

As an aside my observations on this type of day in the Red-tail migration season at the HK site are that many of the Red-tails seen in the PM hours have full crops indicating that they may have spent the morning hunting prey rather than soaring flight conditions. But, if that was so, the kudos should still be presented to Bill James for his inexhaustable research in reminding us all of the fact that we should have known all along. The wind is not as strong in the valley as it is at any altitude above the valley. And, that fact alone is very important in understanding the behavior of hawks in migration.

Dave Holt

Wind

Yesterday, November 1, we had strong wind (B = 2,3) early in the morning (I was there at 9:00 with high hopes), continuing most of the day. I expected lots of RTs, but saw very little until the 12 to 1 period (EDT). I talked with KT at about 10:00 and she said there was no wind in the valley where she was in the morning. I tried to see leaves moving on the ridges, but there was little movement. My impression was that there was wind on the mountain and not in the valley - thus the sparse number of hawks early. But between 12 and 4, we had 33 RTs.

Today, I looked at the weather map from Buchanan for yesterday (November 1st). Here it is:




I had the wind as varying from W, WNW and NW. I had speed at a constant 2 to 3. You can see that the wind in Buchanan did not pick up until around noon.

Here is a map from Roanoke which is lower than the site in Buchanan, I believe:



You can see that the wind speed did not get above 10 MPH until after noon. I believe this data confirms my impression that there was more wind on the mountain than in the valley and that this might explain the lack of hawks until there was wind in the valley. Additionally, there were clouds most of the day with some clearing during the noon hour (10% from previous 70%). It might be instructive to have a similar day with few clouds to determine if hawks could get up using thermals.

This is an exercise in attempting to use data sources to confirm observations.

bj

Broadwing Musings

Subj: [Va-bird] Raptor populations and migratory paths Date: Wednesday, September 19, 2007 10:02:14 AM From: brenda@birdsofvirginia.com To: va-bird@listserve.com, shenvalbirds@yahoogroups.com

It is a documented fact that in our part of the Piedmont here in Virginia, the majority of Broad-winged Hawks and other raptor species will follow along and over north to south ridges during fall migration. For a number of years Bill Minor, John Irvine, Jr., Paul Saunier and others conducted a linear study in the Piedmont that included Rockfish Gap and in each and every year the majority of the birds were concentrated along and over the north to south ridges at and to the north and south of Rockfish Gap and not spread out over the valleys to the east and west. Here in our section of the Piedmont, it is MY belief that when winds are light to moderate and out of the east, the majority of Broad-wings up the pipeline following along the ridges heading toward Rockfish Gap will steer more along a narrow strip of ridges that run southward toward Charlottesville, ESE of Rockfish Gap, and they will either make a wide swing and veer SW to pick up the Blue Ridge directly south of Rockfish Gap or continue southward to Lynchburg area. The data collected by Gene Sattler at Candler Mountain located along the southeast edge of Lynchburg, approximately 45 miles SSE of Rockfish Gap and 32 miles East of Harvey's Knob, would appear to support this theory. On days when winds are light and out of the east, numbers drop significantly at Rockfish Gap UNLESS we are fortunate to catch them streaming and/or kettling far off to the east out over the Piedmont. Oftentimes a spotting scope is required to get a sufficient visual for counting purposes. Data collected at participating hawk watch sites is an important component of migration study especially now with the increasing threat of wind turbine development on top of the ridges along the eastern flyway. It it critical that migration patterns along our mountain ridges continue to be monitored, not only for raptors but bats and other avian species. As to population indicators for certain species such as Broad-winged Hawk wherein the bulk of the population migrates into South America, I would recommend individuals check totals collected at Corpus Christi, Texas and Veracruz, Mexico which provides a better picture of year-to-year population trends. Collected data by participating hawk watches is readily available by going to www.hawkcount.org. One additional note: Yesterday morning at Rockfish Gap, shortly after dawn, there was a "massive" liftoff of Broad-winged Hawk along the western slopes near Waynesboro and to the east along the base. These birds were very close to the ridge and could very well have been some of the birds that flew over Harvey's Knob to our south. The wind was light to moderate out of the NW to N. I later received reports that the wind shifted to variable and east with significant drop in migrating raptors over Rockfish Gap later in the day. Based on reports by Condon and others, it appears the Broad-wing steered along that narrow eastern ridge to head southward over Charlottesville area. Another report has come in that there may have been another late afternoon push of birds over Rockfish Gap. Shift in the winds? Totals to follow.


Subj: RE: [Va-bird] Raptor populations and migratory paths Date: Wednesday, September 19, 2007 7:32:16 PM From: MARLENECONDON@aol.com To: va-bird@listserve.com cc: shenvalbirds@yahoogroups.com

Two comments in regard to this statement posted earlier today: "It is a documented fact that in our part of the Piedmont here in Virginia, the majority of Broad-winged Hawks and other raptor species will follow along and over north to south ridges during fall migration. For a number of years Bill Minor, John Irvine, Jr., Paul Saunier and others conducted a linear study in the Piedmont that included Rockfish Gap and in each and every year the majority of the birds were concentrated along and over the north to south ridges at and to the north and south of Rockfish Gap and not spread out over the valleys to the east and west." (1) Conducting a one-day linear study each year for a few years in a row does not scientifically prove that Broadwings are concentrated along the mountains. It only proves that they were flying along the mountains on that particular day (if, indeed, they were). A linear study would need to be conducted on MANY days in September and for more than a few years, especially on a big day at the mountains, in order to make a definitive statement regarding where Broadwings migrate through this area. I personally know that on many of the high-count days at Afton, there were also big numbers of Broadwings spread out on both sides of the Blue Ridge. I am not familiar with any study that has truly proved that "the majority of Broad-winged Hawks and other raptor species will follow along and over north to south ridges during fall migration." Unless people are down in the valleys to count when hawks are known to be going over Rockfish Gap, you just can't make such a statement. This isn't to say that more hawks aren't counted on mountain tops--it makes sense that they would be because that's where people are looking for them! And, of course, the elevation assists people in spotting them because you may be closer to the birds and with more eyes scanning the skies together, the higher the likelihood of spotting birds that could otherwise be missed. (2) From the September 16 report of this year in which over 6000 Broadwings were counted : "At times, large kettles would flicker in and out in the distance and only with spotting scopes could counters get a clear visual on swirling masses, with hundreds kettling and then streaming out. One impressive flight was over 1,000 that formed several large kettles." Sure sounds like a fair percentage of Broadwings were over the Piedmont rather than above or along the ridges!
Sincerely, Marlene


Subj: Re: Fwd: [Va-bird] 2000+ Broad-wingeds at Warrenton, Fauquier 19 September Date: Saturday, September 29, 2007 7:38:47 PM From: doubtindave@comcast.net To: MikeLPurdy@aol.com --------------

Dave Holt 's reply: The author of this letter could not have been more correct. Broad-winged hawks indeed migrate on a broad front throughout all regions of the eastern United States. A very broad front at most sites but there are a few where the migratory flight is concentrated. The area around Detroit, Hawk Ridge, and Montclair N.J. are sites that come to mind. Sites where natural barriers such as large expanses of water cause the hawks to converge over small areas of terrain over which they prefer to migrate. And other sites along the Atlantic Coast such as Cape May and Kiptopeke. Would that there was a concentrated watch on the outer banks of North Carolina. Alas! Now all of us hawkwatchers who are bound to our sites inland along mountain ridges and maybe in the Piedmont regions are not making any contribution whatsoever to the monitoring of hawk populations. If anything comes from our hobby it is maybe the study of the behavior of hawks in migration. The only scientifically legitimate place for monitoring the population of migrating hawks is in the Isthmus of Panama. Back in the 1970s Dr. Neal Smith spent ten years trying to count them there and found it impossible to do so. Over the thirty years or so that I have been hawkwatching and scanning the data from other sites I have concluded that massive (in the thousands) counts of hawks can be seen from anywhere during the migration season. I have also been satisfied that my hawkwatching efforts have nothing to do with monitoring the populations of hawks and has no contribution to the preservation of hawks. Thousands of people in that enterprise came to the conclusion that the Osprey and Bald Eagle no longer needed protection long before my puny efforts on the hawkwatch came to the same conclusion. But, I still enjoy hawkwatching as it provides me with a question to answer: Why was the hawk I saw in my view in the first place? I am examining, at best, a patch of sky that has a two mile radius. That is an extremely small sampling area when one considers that the hawk one has seen could be anywhere in a billion mile radius. When I have dutifully attended a mountaintop site in the hope of finding thousands of hawks only to be advised by another watcher who was to attend the site that day that he counted 3000 hawks from his home while loading the car to attend the site, I began to wonder why attend the mountaintop site indeed. It is all about that question of : Why was that hawk in my view in the first place? One must place oneself in a place where one can see the most hawks and in our region it is on a ridge top or some hill in the Piedmont that affords one with a near 360 degree view. And it must be a place where we can easily attend as many days as possible during the migration season. Then we must collect and store three aspects of data: weather, hawks, and topography. One of these aspects appears to be a constant and that would be the topography but that can change also. A new clear cut in the nearby forest would have an effect on the thermal density within the purview of the site. So the data collected must be strict and comprehensive. Weather, hawks, and topography strictly recorded will answer the question of "Why was that hawk in my view in the first place?" Anything else is simply scorekeeping among sporting birders . Dave Holt >


Subj: Re: Fwd: [Va-bird] Raptor populations and migratory paths Date: Saturday, September 29, 2007 8:00:42 PM From: doubtindave@comcast.net To: MikeLPurdy@aol.com --------------

Dave Holt replies: I was privy to the linear studies that John Irvine conducted in the vicinity of Rockfish Gap and I saw no control evidence of searching the Valley or Piedmont areas alongside of the Rockfish Gap site during those linear studies. There are plenty of documented sitings from valley and piedmont of massive movements of Broadwings over many of the years that the Rockfish Gap and Harvey's Knob sites were manned. I highlighted the June Crutchfield / Alice Davis finding of 3500 hawks from a point off the east side of the ridge at Rockfish Gap well within the Piedmont when the Rockfish Gap site was clouded in which it often is. Myriam Moore once reported that counting 3000+ Broadwings prevented her from leaving home to attend the watch when no hawks were seen on the mountaintop site at Harvey's Knob. I personally have seen massive Broadwing flights over the city of Roanoke while there were massive flights over Harvey's Knob. And in the past ten years or so there have been several massive flights over Candlers Mountain near Lynchburg that have surpassed the flights over Harvey's Knob. The only time that the Broadwinged flights stick to the ridges is when the prevailing winds are in a ridge crossing direction, either NW or SE . Otherwise the hawks are soaring on thermals and their only direction is southward and the ridges be damned. Dave Holt 9/29/07


Subj: Re: Fwd: [Va-bird] hawks going by to the East Date: Saturday, September 29, 2007 8:46:11 PM From: doubtindave@comcast.net To: MikeLPurdy@aol.com -------------- Original message

Marlene Condon has hit the nail on the head. She asks what value our counts can be to researchers? Absolutely none. No professional researcher would touch our data as it isn't in the least gathered in a professional manner. The counts themselves are fairly accurate I believe but the conditions under which the counts are gathered leave much to be desired. Wind speed and direction are extremely important but most observers only pay attention at the turn of the hour. Visibility is important but there is no standard by which everyone can agree. Cloud cover is useless without knowing the cloud types. We are simply playing games with other sites by keeping score. We get burned and we wonder why but we make no effort to find out why we get burned. We fail to answer the most pertinent question: Why was that hawk in my view in the first place? After all, I am only examining a two mile patch of sky. Am I really interested in why I am seeing the hawk or am I just interested in scorekeeping versus some other site? Dave Holt


Subj: Hawk migration musings Date: Saturday, September 29, 2007 9:23:46 PM From: doubtindave@comcast.net To: MikeLPurdy@aol.com

I am not interested in arguing with birders at large. But I am interested in letting those who are interested know where I stand. The data has to be maintained locally at each site. HMANA does not analyze the data. It never has and it never will as the analysis of the data is not its mission. Its mission is simply to collect and store the data. The so-called HMANA Journal is merely a score keeping publication. Any analysis in the Journal is simply what the local site personnel come up with about the seasons records. The data from each site is stored in file cabinets at the Hawk Mountain Sanctuary to be released to any legitimate researcher who requests it. As you know any researcher would be pressed by time. Would he or she be willing to sacrifice time to look at the data at an obscure site on the Blue Ridge called Harvey's Knob? A site where no one can agree on the cloud cover, visibility, wind speed, or wind direction. I don't think so. We are quite capable of answering the question: Why was that hawk in my view in the first place? At least at Harvey's Knob we are capable of answering that question. We have the data to do so and the inquisitiveness to do so. Dave Holt


Subj: Re: [Va-bird] Raptor populations and migratory paths Date: Sunday, September 30, 2007 12:06:34 PM From: MARLENECONDON To: MikeLPurdy

Gosh Mike, I can't tell you how very much this correspondence means to me. I have more than once seen many thousands of Broadwings in the Piedmont as well as in the Valley. I would report them to the Rockfish Gap hawkwatch site and no one ever bothered to add them to the count. This mystified me since I thought the point was to document how many were migrating, not "prove" that they only go in large numbers over the mountain sites. Thank you so much and please thank Dave Holt as well. I deeply appreciate the time that both of you have taken to answer my musings on the list-serve. Ever so gratefully, Marlene


Subj: Re: Fwd: [Va-bird] Raptor populations and migratory paths Date: Monday, October 1, 2007 6:34:54 PM From: doubtindave@comcast.net To: MikeLPurdy@aol.com -------------- Original message ---------------------- From: MikeLPurdy@aol.com > Hey Dave, > > I got this note from Marlene after I forwarded your reply regarding one of > her posts. > > Mike > >

Dear Mike, Marlene was victimized by John Irvine's notions about hawk migration. I was privy to his so-called linear study and I found that it had no value whatsoever and I think that Marlene suspected the same thing. I was glad to find a comrade in Marlene. Back in the late nineties I submitted a theory about hawkwatching to Myriam Moore. That theory tried to explain why the Harvey's Knob Hawkwatch bested the Rockfish Gap Hawkwatch for the first and only time in twenty years of concurrent coverage of the Broadwing flights. Myriam sent my suggestion to John Irvine and he proceded to criticize it in his publications for the Rockfish Gap Hawkwatch. When I offered rebuttals he dug up some part time hawkwatchers to rebut my rebuttals and so on ad infinitum. I grew weary of shooting down his rebuttals and even discussing the subject with him. It was at that time that I decided to quit HMANA, the VSO, and the RVBC. Hawkwatching requires people who are receptive to new ideas and who seek new frontiers to explain the phenomena that is taking place before our very eyes while on watch. I am absolutely convinced that there is a meteorological/topographical reason for each and every hawkwatching site to observe migrating hawks and that each and every site is limited by its meteorological/topographical orientation. If you are truly interested I will submit that theory and maybe more. Do with this whatever you please. Dave Holt

Subj: Re: [Va-bird] Raptor populations and migratory paths Date: Thursday, October 4, 2007 9:33:23 PM From: doubtindave@comcast.net To: MikeLPurdy@aol.com -------------- Original message ---------------------- From: MikeLPurdy@aol.com > In a message dated 10/1/2007 9:59:32 PM Eastern Daylight Time, > doubtindave@comcast.net writes: > > the 2007 counts at HK has far exceeded the 1995 counts and I do not know what > the prevaling winds were this year. > I think most of the big Broadwing days this year were on easterly winds, if > I'm not mistaken. We were discussing that if not for the East winds Candler Mt. > would probably have gotten the larger numbers. The biggest flights of BWs on > the Tuesday with 4,000+ were pretty much directly overhead, or slightly east > of the ridge, if I remember correctly. It was pretty awesome. It seemed like > Broadwings were coming thru all day. One of the Hollins Univ. groups came up > and got to see over a thousand hawks. Their instructor was telling them how > lucky they were, that this had never happened to one of the Hollins groups, etc. > I > wish you had been up there. > > Mike > We just returned from a three day trip to the Poconos in PA for a visit to Joyce's brother. My general theory has no problem with hawks soaring on ridge crossing winds but my specific theory does have a problem with the numbers you scored this year at Harvey's Knob on easterly winds. They should have been there but where did they come from. More about this later, as I need to recover from a bug-eyed traffic fighting trip down I-81. But, thanks for the confirmation info. I need to look a bit deeper this year into the prevailing winds for the season and what they have been for the past ten years. Just to tickle your interest the prevailing winds from 1975 thru 1995 at Woodrum Field were SE at 9 mph. Wind speed and direction is very important. Dave

Personally, I would like to track the BWs this year from Canada to here in > relation to local weather conditions to perhaps get some idea of how they came > to the Blue Ridge in such numbers. > > bj > > A few years ago Kerrie Kirkpatrick of northern Virginia tracked high number sighting reports of Broadwings via official and anecdotal reports. It was a flight of 10,000 to 15,000 BWs maybe 20,000. She tracked them down to the southern Pennsylvania border (Mason Dixon line). The Snickers gap site had a fairly large flight at the proper time along the track but Rockfish Gap and Harvey's Knob got zilch. If it was a wave of hawks steadily progressing in a wave latitude to latitude it veered eastward. I don't remember the reason I concluded that but it was probably due to the fact that no huge flight showed up at any site south of the Snicker's Gap site. From what she found it did look like a wave, at least, in the southern PA area. But, it did not maintain the appearance of a wave after Snicker's. Southern Pa is where she received the most reports. I think I concluded that a change in weather when the birds should have shown up at the Rockfish and Harvey's Knob sites caused them to disperse. In all the years I have been hawkwatching while privy to information outside of our immediate area I never saw any indication that a wave of migrating Broadwings ever existed other than the above. My own compilations showed peak flights for one season at Washington Mounument (near Hagerstown MD) Rockfish Gap, Harvey's Knob,and Pilot Mt., NC simultaneously. That is on the same date during the same part of the day. I do not believe that there is a wave of migrating BWs that will show up north of southern Texas. You are quite right in assessing the variables but the independent variable will show up at each and every lookout to a different degree. And it will only determine the number of migrants seen not the true number of migrants. For a population monitor a huge number of sites aligned east to west situated as close as possible along a designated latitude all manned at the same time would be necessary. Add to that problem that each and every site along that line, would have to be evaluated over time as to its ability to display to the human eye the maximum number of migrants. It is that last statement that I would like to assign a weight to the Harvey's Knob site. That is probably the best the amateur hawkwatcher can contribute to the art of hawkwatching. DJ