SuAsCo/Nashua Rivers & Beyond Nighthawk Survey

Hi 2009 Nighthawk Survey Observers- 

We would like to thank you once again for all the time and effort that you put into this fall's nighthawk survey. You did a fantastic job and achieved amazing results!

 

As in the past, this final report is intended to provide an overview of this year's fall nighthawk migration in our survey area and what we have learned from it. This year’s count with its El Nino backdrop, very wet June, and very strong fall nighthawk migration probably raised as many questions as it answered but that is what makes the Nighthawk Survey so fascinating and challenging. We strongly believe that this year's survey has played a vitally important role in helping to "fill in some of the blanks" of what we don't know and allowing us to draw some significant conclusions and hypotheses about nighthawk migration in our survey area. You will find the "makings" of several such hypotheses in the materials below and hopefully they are sufficiently provocative to get you to doff your citizen hat and take these hypotheses the next step.

If you are sufficiently moved to want to do some analysis of your own, please let us know and we will send you an Excel-based copy of the complete database for this year's survey plus a summary of observations for the prior four years to play with.

1. Overview of Survey Effort in 2009

2009 has seen an amazing growth in our fall nighthawk survey effort! Six years ago a small group of nighthawk observers in the SuAsCo valleys of the Merrimack basin grew concerned after watching the number of fall nighthawk migrants fall from a thousand or more on a good night in the 1960s to a precious few by the turn of the Century. This group decided that further research was urgently needed into whether this long-term decline was endemic to the SuAsCo (and points east) or was of a broader scale and if the latter, why. A key issue in this regard was whether total numbers of migrants in New England had been declining over the years or NE migrants had simply been switching away from the SuAsCo valleys to alternate routes in NE.

In 2004 we decided to expand our SuAsCo fall nighthawk survey both westward and northward over the Nashua River and towards southern New Hampshire with the goal of systematically measuring changes in nighthawk flows through the broader area over time. In 2004, observers at several sites in the Nashua River in northern MA began submitting reports and in 2005 additional observation sites were set up further south near the sources of the Nashua and Blackstone rivers and further north in NH near the Nashua's juncture with the Merrimack. Over the next three years (2006-2008) survey coverage expanded west to the Connecticut River and north to Concord and Hanover NH with many more observation sites added along the way. These trends continued and indeed accelerated in 2009 as we reached out eastward in response to observers in the Piscatagua basin and westward to folks on the west side of the Connecticut River in Vermont.

A few statistics from this year serve to illustrate just how far we have come in broadening our survey coverage. This fall our observers covered 89 observation sites, up 22 percent from the 73 last year! These sites stretched from Hanover and Concord NH in the north to Belchertown and Millbury MA in the south, and Keene NH and Greenfield MA in the west to the Piscataqua and Charles River basins in the east. Our 89 sites this year were staffed a total of 413 hours, an increase of 119 site-hours or 41 percent over the 294 site-hours last year.  And our total of 601.5 observer-hours this year topped last year’s total observer-hours by 235 hours or 64 percent.  

A tip of the hat to all of you who made this happen!

 

2. Brief Explanation of the Normalization Concept and Calculations

Given the significant increases in observation sites and hours this year, we are providing two different measures of our count totals. The first measure is the actual total value reported into our website and the second, in parentheses, is the adjusted or “normalized” total computed by dividing the total reported number of nighthawks (both feeding and migrating) by the total number of site-hours consumed in achieving the total count. This normalized total is in effect the total average number of nighthawks per site-hour. For example, if 20 nighthawks were seen by 3 observers at observation site X between 5 and 7 PM and 0 were seen the next hour by one observer, then the total count would be 20 nighthawks, the total number of site-hours would be 3, and the normalized total or average number of nighthawks per site-hour would be 6.7. This normalization method is essentially the same as used in the NAS Christmas Bird Counts except that the Nighthawk Survey uses site-hours as the denominator while the Christmas Bird uses field party-hours.

 

As noted above, the reported totals that we focus on in this report are the sum of the feeding and migrating sighting reports. One could certainly argue that the focus should be limited to migrating birds but we are inclined to the proposition that a bird feeding today is probably a bird migrating tonight (or tomorrow). Nonetheless we do agree that analyses should be run using only the migrating totals and if you agree and are so inclined, we would be delighted to supply you with the appropriate database to do these analyses.

3. Overall Observation Results in 2009

 

This year’s total count was a whopping 8,416 nighthawks which almost doubled last year’s count of 4,437 and exceeded our previous high count of 7,502 in 2006 by 914 birds or 12.2 percent. However, on a normalized basis, we averaged a mere 20.4 nighthawks per site-hour this year versus 35.9 in 2006, a difference of 15.5 birds per site-hour or 43.2 percent.

 

Why did 2009 come out first in total count but a distant second when the count data was normalized? One seemingly logical explanation is that the vast majority of the 7,502 total nighthawks seen in 2006 (some 87.2 percent of the total)  were concentrated in large flocks in the Merrimack River Valley and the density of these flocks allowed observers to count far more birds than normal in each site-hour. If so, then why the unusual density of nighthawks in 2006? The answer may well lie in the presence of flying ants mentioned by some observers that year. Nighthawks have long been noted for having a penchant for flying ants and when they are present, the nighthawks literally “swarm” like bees around the swarming flying ants. One of trends that we in the eastern part of our Nighthawk Survey area have noted in recent years is that flying ants in our area have increasingly tended to swarm after the nighthawks have passed through. One of our long-time observers, Steven Sutton, wrote in one of his daily reports a couple of years ago as follows:

 

“Just a tidbit regarding flying ants. In my personal observations in Lancaster, Bolton, and Harvard [MA], …I have not yet found any association between flying ants nights and the presence of nighthawks. Here in South Lancaster, the flying ant swarms have typically been well after the peak of nighthawk migration. For example, we just had flying ants here last night (September 19, 2007). Although I haven’t kept ant dates, I do recall the pattern being similar over the past few years”.

 

Veteran MA nighthawk observers well to the south and west of Lancaster, Bolton, and Harvard would likely disagree with Steven about the impact of flying ants on nighthawk migration in their area but those to the east might ask, “is that why our numbers of migrant nighthawks have been falling through the floor over the last forty years?”

 

Lance Tanino put a somewhat different spin on the flying ant issue based on his experience along the Connecticut River in the Keene NH area over the past two years:

 

“In 2008, Chimney Swifts were seen in very large numbers (flocks sizes of hundreds along the CT River) early in August feeding on flying ants with a few Common Nighthawks joining the feeding frenzy.  I only observed nighthawks when southerly winds or calm conditions and mosquitoes were prevalent.  No nighthawks were found when winds blew out of the north.  In 2009, very few Chimney Swifts were observed during the entire season.  Flying ants were finally observed during the first week in September and that also happened to be when the largest nighthawk flocks were seen in Keene.  People have commented on those northbound nighthawk flocks during the season.  I personally think and noticed that northbound nighthawks were searching for flying ant swarms and not necessarily “migrating” north.  I don’t know if others have noticed it but nighthawk flocks seem to be found in front of an approaching rain cloud/squall”.

 

For those of you who are Citizen Scientists at heart, here is a wonderful opportunity to do a literature search into what has been happening to flying ant populations in our Nighthawk Survey area and beyond.

4. Breakdowns of the 2009 Count by Major River Basins

One of our major accomplishments over the past few years has been to automate and expand the geographic segmentation capability in our data management system to allow us to break down our observation data electronically into a host of different geographic patterns. Four such breakdowns have proven particularly useful in assessing overall annual and multiyear trends. These four breakdowns are by: (i) major river basins (five in 2009) in our survey area, (ii) major tributary rivers (eleven in 2009) in those basins, (iii) the cities and towns (49 in 2009) where our observation sites were located, and (iv) the specific locations or sites (89 in 2009) in the cities and towns where the observations occurred. Each of these four levels or segments of data provide important insights into each year's migration.

Totals for the five major basins in our survey area this year are shown in the following table. The first number in each row is the reported total count of nighthawks in that basin, and the second number, in parentheses, is the normalized count.

Headwaters of the Blackstone River Basin: 642 (24.7)

Charles River Basin: 30 (60.0)
Connecticut River Basin: 2,919 (29.8) 
Merrimack River Basin: 4,774 (16.6)

Piscataqua River Basin: 51 (34.0)

   Total Survey Area 8,416 (20.4)

 

This year (2009) our total count in the Merrimack River Basin soared to 4,774, more than triple last year’s count of 1,546, and the normalized total rose from 7.7 in 2008 to 16.6 nighthawks per site-hour. In contrast, the Connecticut River Basin total count this year was 2,919, up only 4 percent from 2008’s count of 2,810, underscoring that the Merrimack was certainly the preferred corridor south through NH in 2009. On the other hand, the Connecticut did maintain its substantial lead over the Merrimack in average number of nighthawks per site-hour with a normalized total of 29.8 in 2009 (down from 35.3 in 2008) versus the Merrimack’s 16.6 this year.

 

The dominance of the Merrimack Basin in total counts this year comes after two years of falling numbers in that basin. As mentioned earlier, some 87 percent of the total nighthawk count in 2006 came from the Merrimack Basin but those percentages dropped precipitously to 65 percent in 2007 and 35 percent in 2008 before rebounding upward to 56.7 percent in 2009. During that same period, total counts in the Connecticut River Basin rose over 900 percent in 2007 versus 2006, 85.6 percent in 2008 versus 2007, and 3.9 percent in 2009, due in large measure to increased numbers of sites and observers plus substantial rises in the average numbers of nighthawks seen per site-hour in that basin. The normalized values in the Connecticut Basin in those three years were 16.5 in 2006, 30.0 in 2007, and 35.3 in 2008.

 

Interestingly, the headwaters of the Blackstone River Basin show much the same pattern as the Merrimack River Basin with high total counts in 2006 and 2009 and sharp dips in 2007 and 2008. The Blackstone’s highest annual count was in 2006 with a total of 796 nighthawks. In 2007 the count sank to 289, down 64 percent from 2006 and in 2008 the total was 81, down 72 percent from 2007. In 2009 the Blackstone’s total bounced back up to 642. The normalized totals were 43.0 in 2006, 36.1 in 2007, 6.2 in 2008, and 24.7 in 2009. The fact that the Blackstone and Merrimack have similar count patterns is not terribly surprising inasmuch as both basins run N-S with the Nashua River flowing north from the Worcester area to connect with the Merrimack at Nashua and the Blackstone River flowing south from the Worcester area through Connecticut and out into the Atlantic. On the other hand the fact that the counts in the two rivers show similar interannual patterns suggest that the same independent variable(s) may be at work in both basins.   

 

5. Breakdown of 2009 Count by Major Tributaries or Watersheds.

 

The following table shows our total and normalized counts in each of the major tributary or watershed in our survey area in 2009:

Blackstone River Basin Total: (headwaters only): 642 (24.7)
   Blackstone Watershed 642 (24.7)

 

Charles River Basin Total: 30 (60.0)

   Charles River Watershed: 30 (60.0)

Connecticut River Basin Total: 2,919 (29.8)
   Ashuelot: Watershed 1,999 (50.6)
   Chicopee Watershed 0 (0.0)
   Connecticut Watershed 403 ((9.0)
   Millers Watershed 9 (1.3)
   Swift Watershed 508 (6.5)

Merrimack River Basin Total: 4,774 (16.6)
   Contoocook Watershed 398 (20.9)
   Merrimack Watershed 959 (30.4)

   Nashoba Watershed 2 (4.0)
   Nashua Watershed 1,583 (27.5)
   SuAsCo Watershed 1,832 (10.3)

 

Piscataqua River Basin Total: 51 (34.0)

   Salmon Falls River: 51 (34.0)

 

Total Nighthawk Survey: 8,416 (20.4) 

The above data suggest that this year the Ashuelot River was the major driver in the Connecticut River basin for both the basin’s total count and its normalized count. The Ashuelot’s total count accounted for 68 percent of the Connecticut Basin's total count and the Ashuelot’s normalized total of 50.6 nighthawks per site-hour clearly drove the 29.8 normalized total for the basin as a whole. The Ashuelot’s total this year was up 20 percent from 2008 and its normalized total was up 45 percent. Other substantial contributions this year came from the Swift River and parts of the Connecticut both north and south of Keene. The Swift River total of 508 was down 34 percent from last year and its normalized total was down from an extraordinary 96.4 nighthawk to a still very good 78.2.  The total of 403 nighthawks counted along the banks of the Connecticut River north and south of Keene was up 10 from last year but the normalized total of 9.0 versus 19.7 last year suggested that observers had to work hard for those last 10.

 

In the Merrimack River basin, an extraordinary thing happened this year… the usual doormat, the SuAsCo watershed, came in first!!! This year’s SuAsCo total count of 1,832 was six times as high as last year’s total of 306. Does this mean that the SuAsCo’s steady decline in nighthawk migrants over the past 50 years is finally over? Definitely not. This year’s 10.3 normalized value is 5 times higher than last year, suggesting a significant uptick in total migrants but it is still well below the rest of the Merrimack basin and is in large measure attributable to a significant uptick this year in the numbers of observers and sites in the SuAsCo area which in turn have been triggered by rapidly growing public awareness and interest in both citizen science in general and the nighthawk problem in particular. In early August this year we organized a program jointly sponsored by the Friends of the Assabet River and Oxbow NWRs, the Sudbury Valley Trustees, and the Organization For The Assabet River to present a nighthawk briefing coupled with follow-up field trips to hone participant identification skills. That program, alone, added 30 highly motivated observers.

 

The second most productive tributary in the Merrimack basin was the Nashua River Watershed with a total count of 1,583 and a normalized count of 27.5 nighthawks per site-hour. This year’s total count more than doubled last year’s 647 and the Nashua’s normalized total for 2009 was up 21 percent. In third place in the Merrimack basin this year were observation sites along the Merrimack River itself. These sites produced a total count of 959 nighthawks and a normalized count of 30.4. Not surprisingly, a major part (789) of the 959 total nighthawks listed under "Merrimack Watershed" came from the Concord NH area. The 959 total this year was almost three times higher than last year’s 322 but interestingly, last year’s normalized total of 80.5 was more than twice as high as this year’s 30.4. The 80.5 presumably reflects large high-density flocks in the Concord area last year and/or failure to report bagels..

 

Finally, the Contoocook River Watershed led by Don and Lillian Stokes followed the upward trend (as compared with 2008) shown by the other Merrimack basin tributaries and posted a 2009 total count of 398, up 47 percent from last year’s 271. Both years were only about a third of the totals achieved in both 2006 and 2007. This year’s normalized total of 20.9 was down slightly from the 21.7 in 2008. These numbers were 5-7 times lower than in 2006 and 2007, suggesting a steep decline in the size and density of flocks headed down the Contoocook.

 

6. Breakdown of 2009 Count by Cities and Towns

The following table breaks out our 2009 totals by the cities and towns where the nighthawks were observed and ranks these cities and towns by the total number of nighthawks reported. The first number in each row is the total for 2009; the second number (in parentheses) is the 2009 normalized total; and the third percentage increase or decrease of the 2009 total versus the 2008 total count.

 

Keene NH - Connecticut watershed  1,731 (38.8) +8.8%
Concord NH - Merrimack watershed  789 (52.6) +146.6%
Millbury MA - Blackstone watershed  642 (24.7) +1,326.7%

Hollis NH - Nashua watershed  625 (22.3) +163.7%
Lincoln MA – SuAsCo watershed  579 (17.8) 0 in 2008 + infinite %

Belchertown MA  - Swift watershed  508 (78.2) -34.1%
Harvard MA - Nashua watershed 413 (28.5) 0 in 2008 + infinite %

Hancock NH - Contoocook watershed  398 (24.1) +56.1%
Westminister MA  - Nashua watershed  387 (51.6) +31.2%
Concord MA - SuAsCo watershed  340 (10.6) +2,990.9%
Westmoreland NH - Connecticut watershed  280(56.0) +976.9%
Swanzey NH - Ashuelot watershed  265 (44.2) +3,212.5%
Wayland MA - SuAsCo watershed  217(7.8) +393.2%
Stow MA - SuAsCo watershed  173 (49.4) 0 in 2008 + infinite %

Groton MA - Nashua watershed   151 (21.6) +54.1%
Northborough MA - SuAsCo watershed  121 (2.8) +137.3%
Maynard MA - SuAsCo watershed  116 (11.6) +2,800.0%

Sudbury MA - SuAsCo watershed  99 (6.6) +191.2%
Manchester NH - Merrimack watershed  92 (13.1) 0 in 2008 + infinite %

Boxborough MA - SuAsCo watershed  80 (80.0) 0 in 2008 + infinite %

Rochester NH - Salmon Falls/Piscatagua  51 (34.0) 0 in 2008 + infinite %

Nashua NH - Merrimack watershed  49 (6.5) 0 in 2008 + infinite %

Lyme NH - Merrimack watershed  47 (11.8) -39.0%
Natick MA - SuAsCo watershed  38 (19.0) -22.4%

Boston MA - Charles River watershed 30 (60.0) 0 in 2008 + infinite %
Londonderry NH - Merrimack watershed  29 (14.5) +1,350.0%

Hanover NH - Connecticut watershed  28 (1.0) -9.7%

Walpole NH - Connecticut watershed  23 (11.5) -56.6%

Newport NH - Connecticut watershed  20 (40.0) 0 in 2008 + infinite %

Southborough MA -SuAsCo watershed  16 (8.0) 0 in 2008 + infinite %

Holliston MA - SuAsCo watershed  15 (30.0) 0 in 2008 + infinite %

Westborough MA - SuAsCo watershed  14 (28.0)

Hudson MA – SuAsCo watershed  11 (7.3) 0 in 2008 + infinite %

Athol MA - Millers watershed  9 (1.3) -60.9%

Pepperell MA - Nashua watershed  7 (14.0) 0 in 2008 + infinite %

Charlestown NH - Connecticut watershed  5 (1.0) -93.3%
Framingham MA - SuAsCo watershed  5 (0.9) +400.0%

Marlborough MA - SuAsCo watershed  5 (5.0) +150.0%

Hopkinton MA - SuAsCo watershed  3 (6.0) 0 in 2008 + infinite %

Bolton MA - Nashoba watershed  2 (4.0) 0 in 2008 + infinite %

Stoddard NH - Ashuelot watershed  2 (1.0) 0 in 2008 + infinite %

Winchester NH - Connecticut watershed  1 (2.0) 0 in 2008 + infinite %
Surry NH - Ashuelot watershed  0 (0.0) 0 in 2008
Peterborough NH - Contoocook watershed  0 (0.0) -100.0%

Chesterfield NH – Connecticut watershed  0 (0.0) 0.0%

Hinsdale NH – Ashuelot watershed  0 (0.0) 0.0%

Spofford NH – Connecticut watershed  0 (0.0) 0.0%

The totals and rankings are noteworthy in several respects. The total for #1 Keene of 1,731 is, in our collective recollections, the highest total recorded for a single municipality in the history of the survey. A tip of the hat to Lance Tanino and his colleagues! Second place goes to Rob Woodward and his associates in NH’s Capitol City of Concord with a total of 789 and third place goes to Alan Marble, the silent shopper of the Shoppes at Blackstone Valley in MA who garnered his 642 nighthawks about as far south from Concord NH as is possible and still be in our survey area.

 

At least as remarkable as the Keene numbers are the 579 total (#5) seen by Norm Levey  at Mass Audubon’s Drumlin Farm in Lincoln MA and the total of 413 (#7) put together by Rona Balco and her crew at the Oxbow NWR in Harvard MA. Neither of these observation sites were active last year but they sure came to life with a bang this year. If anyone would like to read a fascinating and thought-provoking account of the survey on a day-to-day basis, go to our nighthawk survey website and thumb through Norm’s comments in the “detailed daily reports”. This is reporting at its best!

 

Below is some food for thought for next year. The following municipalities (with last year’s results) were not covered this year but have proven to be productive in bygone years:

 

Greenfield MA - Connecticut watershed  100 (200.0)
Shrewsbury MA - Blackstone watershed  36 (10.3)

N. Walpole NH - Connecticut watershed  31 (62.0)
Princeton MA - Chicopee watershed  24 (48.0)
Fitchburg MA - Nashua watershed  15 (15.0)
Carlisle MA - SuAsCo watershed  5 (0.8)

Chelmsford MA - SuAsCo watershed  4 (8.0)
Sterling MA - Nashua watershed  2 (4.0)
Berlin MA - SuAsCo watershed  1 (2.0)
Billerica MA - SuAsCo watershed  NR

 

7. The Top Ten Sites

 

Drum roll, please! The top ten observation sites in 2009 were:

 

NH Legislative Parking Garage Concord NH – 789 (52.6)

Court Street (North End) Keene NH – 579 (27.6)

MAS Drumlin Farm Lincoln MA – 579 (18.4)

The Shoppes at Blackstone Valley, Rt. 146, Millbury MA – 554 (33.6)

Brentwood Golf Course (South End) From Rt. 12A, Keene NH – 522 (348.0)

Aldrich Street, Belchertown MA – 508 (78.2)

Oxbow NWR Watts Field, Harvard MA – 413 (28.5)

Beaver Brook Association Wildlife Pond, Hollis NH – 401 (114.6)

Powdermill Pond, Hancock NH – 398 (24.1)

High Ridge WMA, Westminister MA – 387 (51.6)

8. Analysis of Daily Total Counts: Possible Impacts of El Nino and Global Warming

Up to this point our analyses of the survey database have of necessity been largely limited to annual summaries in order to keep this report within reasonable bounds. But the potential is there to analyze migrations flows on a day-to-day basis.

One of the facets of this year’s count that we have found fascinating is an apparent shift in the pattern of the buildup and decline of migrating nighthawks in our survey area. During the latter half of the 19^th Century the buildup and decline generally followed a bell-shaped curve, at least in this area, with the peak occurring close to August 25. Then in the early 2000s the peak began to move slowly towards the end of August and in both 2006 and 2007 the peak for our count area as a whole occurred on August 30 but then rebounded in 2008 to August 23.

 

But this year something odd occurred. The curve flattened out and three separate peaks appeared, one centering on August 23-25, a second centering on August 30 and the third centering on September 3. See the table below.
                                                2006               2007               2008              2009

Blackstone Basin                 8/31                8/28                8/29                 9/2

Connecticut Basin               8/24                8/30                8/23                 9/3
Merrimack Basin                  8/30                8/29                8/28                8/25
Total Survey Area                8/30                8/30                8/23                8/30

 

These peaks could possibly have been caused by weather systems in the survey area. The peak of August 23-25 was preceded by a period of unsettled weather – cold front-induced thunderstorms on August 21 and Hurricane Bill passing to the east on August 22. And the peak on August 30 followed a rain event on August 28-29. On the other hand, there was no notable weather event preceding the September 3 peak and rain events have certainly occurred in previous years that did produce the sorts of delays seen this year.

 

Peak count dates for the past four years for the individual watersheds with sufficient observations to be meaningful were as follows:

                                                2006              2007              2008                2009

Ashuelot                                 NA                 8/30               8/30                 8/30             
Blackstone                             8/31               8/28               8/29                 9/2              
Contoocook                           8/22                9/8                 8/22                8/25                              
Connecticut                           8/28               8/28               8/28                 9/3                     
Merrimack                               NA                8/29               8/27                 8/26
Millers                                     8/24               8/25               8/29                  NA
Nashua                                  8/30               8/27               8/29                 8/30
SuAsCo                                 8/30               8/28               8/23                 8/24
Swift                                        NA                 NA                8/23                 8/24

Clearly there has been a marked and accelerating movement towards increasingly later nighthawk migration in our survey area in recent years. An interesting statistic in this regard is that this year for the first time some 30 percent of our total count came in the first three days of September and reflects the flattening out of the bell curve and appearance of a third peak of migrants in early September. (Recently we received a belated report from one of our regular observers that at least 300 nighthawks and possibly upwards of a thousand were seen September 3 feeding on flying ant swarms at the Keene NH Rec Center. If the confirmed 300 are added to this year’s count of 8,416 as they presumably will be, the first three days of September will have contributed 32.8 percent or almost a third of this year’s total count!

 

What’s the cause of this shift into September? One possibility is a significant increase in later-migrating first-year migrants due to higher breeding rates caused by the much wetter than normal spring, perhaps resulting from the current El Nino episode. A second possible weather-related cause is global warming and, in particular, warming impacts on flying insect populations during migration. Stay tuned for more on these issues next year.

 

Again, many thanks for your help and best wishes for the coming year. We would also like to extend you an early invitation to come join us for the 50^th Anniversary of the Concord (MA) Christmas Count on Sunday, January 3, 2010!

 

                                                           Hank Norwood and Jeff Slovin