I promised to find some things we could say about 24 years of hawk-watching by analyzing the data, and I found some answers to things I was curious about. I gave several ways the data was set up, and what info was expected by record keepers. Let me rename them:
#1. By kind of bird
#2. By total number of raptors/yr
#3. By number of days
#4. By number of hours
#6. By weather and other local conditions for each day
#7. By ratios of these things and how they compare to other years strictly as numbers.
#8. By unique individuals seen – or numbers on the increase/decrease
We have kept the kinds of raptors seen from our watch now, for 24 years. Therefore, next year we will have a quarter century of ongoing data. And it has been the unique benefit of our generation to be able to make the data public because of the internet and social media, and websites. And I mean "we" as a whole community of hawk-watchers.
Most web-sites however post pure data. A few have Facebook pages which, like ours, post or link to daily data as it is counted. Some are able to post pictures of great finds of individual birds, or discuss the ways to ID a unique bird. We have tried to do some ID blogs here. Although, many have come bringing great lenses, our site doesn't lend itself to super pictures of hawks, because many raptors are able to attain great heights above our site, quickly in the day.
But the data, which the guys collect, isn't put up from their notebooks each day. Not as it's collected. One of the things I would like to do next year, is give a full year's reports, showing a picture of the data page, exactly the way the guys collect it. I wish I had done it sooner, thereby making that detailed data viewable by anyone. There are interesting bits of info that can be gleaned from those pages.
But for the most part the data is presented publicly in a very simple form. An end of the year Chart. With columns for the Initials of individual species showing first and foremost, the kinds of raptors seen. (#1)
Listed across the top of the chart, for our watch, it looks like this:
The charts, as I have said in previous posts, are located on the STATS FROM THE PAST page of this blog. Last Blog, I discussed that the charts evolved to be yearly lines only due to the changing of my available software, time constraints, and the need to post info significant to that year alone. I also repeat here that the "standard" lineup of birds is as they appear on the chart. For simplicity, and for anyone who has not learned the meaning of the Initials: They represent the birds in the following order:
Osprey, Mississippi Kite, Bald Eagle, Golden Eagle, Northern Harrier, Sharp-Shinned Hawk, Cooper's Hawk, Northern Goshawk, Red-Shouldered Hawk, Broad-winged Hawk, Red-Tailed Hawk, Rough-legged Hawk, American Kestrel, Merlin, Peregrine Falcon, Turkey Vulture, Black Vulture, and the unidentified raptors.
So thus we have kept the records, by kinds of birds, as totals for the season into each column year by year.
This chart also has a column for the Total number of Raptors seen each season. (#2) And that is what I want to use to shed some light on just what those totals show. I have arranged those totals from the highest to the lowest number of raptors seen into a chart, and added a column for one species to show how we could discuss the date in a number of ways. Since many of our largest numbers revolve around Broad-wings, and we have gathered the most data during BW season, it is the most reasonable raptor to use for this example.
I will say now and remind you later, that Broad-wing season is the only migration that was consistently covered throughout the years for our site. There are lots of reasons, mainly due to manpower restraints. However, an interesting thing occurred down through the years. Which the data upholds. Exactly 1/2 of the years the BW figures dominate, and 1/2 of the years the data is variable, due at least in part to the inclusion of hawks seen during October through December, because of a dedicated attempt to include at least some data during those months. Bill did his best to make 2016 one of those years.
Here's the chart:
The grand total of all those hawks is: 83,537. It was very satisfying when I reran the figures in a new order, that I came up with the exact same figure as my ongoing count figure. But I was curious what would the average number of birds/year be. From an analytical standpoint, we can determine percent comparisons, specifically BW's versus other raptors (#5), for our site.
Remember- we are using count data, not attempting to make that data represent all of actual numbers of hawks that may have passed our site, which we couldn't count. Percentages are dependent on our numbers.
83,357 divided by the 24 years is a 3,480 bird average.
Likewise, BW grand totals are 61,816 birds, which again matched my ongoing totals, thankfully. That number divided by 24 years gives an average of 2,576 BW's/year. Shown as a percent of BW's to the whole number of raptors, it is 74% BW's.
It is not surprising considering that at least on half of our years concentrated on BW flights.
When I took the individual percents by year, I was able to add that to the chart as follows: (#6)
Exactly 1/2 of the years produced percents of BW's at over 75% of all species seen. Two years were the lowest percentage at 31 - 1994 and 1999. Less than 1/3 of the birds those two years were BW's! These two years were probably due to not enough persons able to get full coverage of any one season. But it is data. And as Jimmy says, to be sure, you still have to look at hours and days, one of the many reasons for the data being kept on those items. (#4 and #5) I won't look back at this time, so I can keep my train of thought concerning percentages.
If I add the percentages for these 12 years, under 75%, I have a high of 72% and a low of 31% twice. A variety of figures, from which we get a total of 650% for 12 years; dividing by 12 an average percent of 54%. In other words, even in the years of wider coverage, a little over half the birds counted were BW's.
Some might think I should eliminate our greatest year for BW's, since we believe it to be an oddball year. But the stat's won't change because, there are 4 other years with even higher BW percent.
For ease of analyzing: the years over 75% are - 2015, 2002, 2009, 2012, 2006, 2014, 2013, 2010, 2005, 2011,2008, and 2007. Even the missing years of 2003 and 2004 come in at 65.7% and 67.9% respectively, for BW's. That affirms the premise which we know exists, that the years we concentrated on BW season are also the years when 75+% of all hawks seen, were BW's. But I believe that even with good numbers of Red-tails and Black Vultures being counted, a number under 75% would probably still hold true. In our area, I simply don't remember seeing numbers of TV's that exceeded 800 birds, when I saw the huge numbers elsewhere. It would take a lot of those figures on a regular basis to overwhelm the totals of BW's seen.
So did we see more Broad-wings than other birds combined? Yes, by 50% more. Half as many again BW's to all other Hawks combined. In fact, the middle of the day high birds that we couldn't count, and only assumed were there, would have raised those figures much higher. If we had been at a higher elevation, we might have raised those numbers even more. But, we aren't analyzing what ifs. Only, the actual counts.
No where in the charts are the numbers of watchers recorded. I personally wish I was anal enough to actually go back and figure them in. I genuinely believe the count numbers increase when numbers of watchers also increase.
We've discussed the total number of hawks compared to BW's. But I won't submit you to those figures for each species. But I can discuss the remaining species in other ways and I have developed a chart for doing that. In my notes, I made myself a reminder to make a new chart that shows hawks per hour. And I might do that as my final post about 2016's stats.
But for now, this chart gives the totals of all other raptors, their best year, and if the numbers indicate an increase or decrease.
This observation, is only as it relates to the numbers we have. It is a shame, as Bill relents often, that we do not have better late season data. We can't actually say the numbers for birds that migrate later that BW's are on the decrease. We can only say that our figures for these birds are a decrease from the earlier years that were well covered across the season. But it does confirm something. These birds definitely migrate later than BW's for the most part! All data tells us something.
I can't help but be surprised at some of these totals. I didn't double ck them all. So let's say for the sake of an error, we can still draw some conclusions, including (#8) the increase or decrease of raptors in our counts. I obviously could take the figures and compare them to the grand total of over 80,000 birds, but I think it's pretty obvious how small those percentages would be. The largest of these, the TV's, at almost 10,000 isn't quite 1/8 of the birds seen. All the others are decidedly smaller fractions.
In my notes, I wrote some of the things that I saw occurring with the numbers. For instance, we saw more Golden Eagles during hacking years. Makes sense. But a couple of things I kept noticing while looking at the yearly charts, was there frequently were back to back years, which some totals were near or identical to one another. I though it was very interesting that the numbers would be so close. It made me wonder if we actually were seeing the same birds following the same route in those years. Merlins in the last 3 years are a good example. In 2014, I told the guys about 2 more Merlins I had seen, but they would not count them because I didn't have a backup person to ID. And the one counted was pretty much because I was determined I knew what I was seeing and insisted they count it. I felt a little bit affirmed when both last year and this year, we also saw 3 Merlins. I have to wonder if they are the same birds. Can't know for sure, but I wonder.
Something similar happens with Bald Eagles. This year we had obvious locals in abundance, for the first time on our count. Yet we still counted 35, only 1 less than the year before. But let's look at the Bald Eagle's stats specifically by year: 3, 3, 15, 18, 18, 41, 25, 23, 34, 35, 24, 27, 8, 20, 5, 6, 22, 6, 21, 25, 29, 36, 35. Notice how many times the number for back to back years are almost the same. Now let's remove the low numbers so we can see what most year represent:
15, 18, 18, 41, 25, 23, 34, 35, 24, 27, 20, 22, 21, 25, 29, 36, 35. Those numbers are closer than with any other species. I find that this is too close to ignore. We must be seeing some of the same birds. And some of those are pairs with their offspring when we see them. Families of Eagles learning the route together. When we frequently see the same birds returning to same areas to nest, it is not farfetched to assume we are seeing at least some of the same BE's year after year. Maybe the young don't survive at a great rate, and of course some older birds die off. Or the numbers now would be significantly higher. A good investigation on their numbers would be to compare them to the number of hours. And see if our perception changes.
The last thing I gleaned from our Data at this point was that we now know what the top 5 birds are: BW, TV, RT, SS, and BV. The top 10 adds: CH, BE, AK, NH, and RS. I love that the numbers of Bald Eagles exceed the numbers of Kestrels. But was surprised that the Numbers of Northern Harriers we've counted exceeds the numbers of Red-Shouldered Hawks.
There are some obvious misses, and lots more to be learned. I am sure there are questions that can still be asked. There should be a chart to relate the weather as an actual document, not just our perception that the hawk numbers increase before and after cold Fronts. Especially ones with lots of rain. And of course I still think it's important to at least do a "days and hours" chart.
But the one thing I haven't mentioned at all are the unique individuals that we have seen.(# 8) In all these years we have only managed to count 3 Mississippi Kites, 1 Northern Goshawk, and 1 Rough-legged Hawk. The rarest of our species. But there have only been 61 Merlins, and 18 Golden Eagles. I didn't get to see the NG or the RL, and am not sure I could have ID'd them at the time. But I feel so privileged to have seen the Kites, Eagles, and Merlins. I likely would have not seen them had we not put in the hours. I have seen them at other times, in other places, but I am very proud to have been on the hawk watch when we counted some of these relatively rarer of the migrants.
Well, it's been a long blog, I know. But hopefully the numbers are engrossing to some of you as well. I, now, don't just know the numbers, I know what those number tell us. Based on 8 basic criteria. (with the present exception of the weather stats, which will take me a little work to arrive at conclusions. I will need to spend some hours there.)
I can end the season of 2016 knowing more than I did. I have some actual facts to share with the Tennessee knowledge of raptors migrating in fall through our state. It is some of what data watchers in the 1930s to 50's wondered about. It is an important documentation of what 24 years of migration has looked like, to the extent we were physically able to collect the data. And now it has been analyzed for answers that have never been known before. Sadly, we don't have significant data to compare it to from years prior to the 90's. But there is some data there, in someone's records. And if it could be combined over any period of multiple years, we could do a great comparison with ease to know how the old migrations compare to today's. Is there that much data from one site, can we compare it legitimately to our data. Or can we just compare that data to itself and then see how it compares to our site?
Jimmy found some of those old numbers. Who knows if one day it's our destiny to research them out and make that comparison ourselves. If anyone out there, would like to and is able...we would love to post it here.
So until Spring at least, I have only a couple more posts about the 2016 season that I want to make, and we will close it out.
SAYING-
KEEP LOOKING UP!!!!
HAPPY NEW YEAR EVERYONE!!!!
No comments:
Post a Comment