Roseate terns (Sterna dougallii) disperse from nesting sites in northeastern North America in late summer and use several coastal locations as staging and roosting areas. Shealer and Kress (1994) found staging and roosting roseate terns from eight different nesting colonies in the northeast in August at Stratton Is., Maine.
On Cape Cod, Massachusetts, peak numbers occur in early September when common terns (S. hirundo) and roseate terns flock together in large concentrations before migration. South Beach, Chatham, Massachusetts supported 11,000 common and roseate terns on September 1, 1998, 35% (n=3850) were estimated to be roseates. Between mid-August and mid-September large concentrations of roseate terns use two primary sites as roosting areas and one as a staging area on Cape Cod. South Beach, Chatham, and Sandy Neck, Barnstable, were roosting sites while Coast Guard Beach, Eastham was a major staging area. During two aerial observation flights on September 8 and 18, large flocks of terns (n=1000), which were difficult to separate specifically, were observed at Jeremy Point, Wellfleet, indicating a major staging area for common and roseate terns which needs further investigation. Cape Cod supports the largest pre-migratory concentration of roseate terns in North America, with the largest numbers occurring between August 20 and September 10.
Roseate terns disperse from nesting sites in northeastern North America in late summer and use several coastal locations as staging and roosting areas. Shealer and Kress (1994) found staging and roosting roseate terns from eight different nesting colonies in the northeast in August at Stratton Island, Maine. On Cape Cod, Massachusetts, peak numbers occur in early September when common terns and roseate terns flock together in large concentrations before migration. The purpose of this study is to define the period and extent of use that roseate terns depend on specific areas on Cape Cod, prior to their southern migration in fall. South Beach, Chatham, Massachusetts, supported 11,000 common and roseate terns on September 1, 1998, 35%, of which (n=3850) were estimated to be roseates. Between mid-August and mid-September large concentrations of roseate terns used two primary sites as roosting areas and one as a staging area on Cape Cod. South Beach, Chatham and Sandy Neck, Barnstable were roosting sites while Coast Guard Beach, Eastham, was a major staging area. During two aerial observation flights in September, large flocks of terns (n=1000), which were difficult to separate specifically were observed at Jeremy Point, Wellfleet, indicating a major staging area for common and roseate terns which needs further investigation. Cape Cod supports the largest pre-migratory flocks of roseate terns in North America, with the largest concentrations occurring between August 20 and September 10.
Following the guidelines of the Roseate Tern Recovery Plan we have:
1) Conducted surveys to locate and define the staging areas used by roseate and common terns prior to their fall migration;
2) estimated approximate peak numbers of both adults and young using each site;
3) identified the chronology of use of each area; and
4) identified the periods of the day that staging and roosting areas are used.
In addition, we have described and assessed each form of disturbance to staging/roosting terns at each site. Other management concerns will be addressed through recommendations upon completion of this report.
Fifteen sites in southeastern Massachusetts were monitored by observers during July, August and September, 1998, ranging from the mouth of the North River, Scituate, south along Cape Cod Bay to Hatches Harbor, Provincetown, south along the eastern shore to South Beach, Chatham, including the Monomoy National Wildlife Refuge. Nantucket, Muskeget Island, Tuckernuck Island, and Martha’s Vineyard were also included in the study area (see map for specific sites). Historic sighting records published in Bird Observer of Eastern Massachusetts between 1982 and 1997, and an unpublished report to the Massachusetts Audubon Society (1994), were reviewed as the basis for selecting study sites in 1998. Each of the fifteen sites had had at least one reported sighting of 100 or more roseate terns over the period between 1982 and 1998.
During the 1998 study, seven sites were simultaneously monitored over a six-week period. Observers counted standing flocks of birds singly, by tens or by making density estimates based on prior field experience. Common-to-roseate tern ratios were estimated by sampling flocks of over 100 birds when possible, but this was often arduous due to the restless nature of the terns. The same was true for the adult-to-juvenile roseate tern ratios. Seven observers compiled 76.75 hours of data during a total of 38 site visits. The observation periods averaged just over 2 hours. The study began on August 18 and was completed on September 22. Each observer covered one of seven sites to be monitored on the same day each week (Tuesday) during the late afternoon until dark. This period was chosen because one main objective of the study was to record the numbers of roseate terns using nighttime roosts, and to identify these nocturnal areas. Several random diurnal site visits were made prior to and during the study period to identify potential sites and to monitor daytime activity of terns as well as to assess disturbance.
Prior to this study, researchers and field observers generally referred to any site supporting large concentrations of terns during the post-breeding period as a “staging area.” In this study, a staging area is defined as an area where concentrations of mixed species of terns, predominantly common and roseate, spend the daylight hours resting and feeding. Typically, these areas are remote, relatively undisturbed, and adjacent to a dynamic inlet or otherwise active tidal inlet where food is easily obtained with minimal expenditure of time and energy. One would postulate that weight gain through fat deposits prior to and essential for migration would occur at these sites. Though likely, no data have shown this related to the Sternidae. Populations of several species of sandpipers and plovers depend on strategic migration staging areas where they do put on fat reserves prior to long distance migrations (Myers et al., 1987). On Cape Cod and other eastern locations, these strategic sites tend to be coastal (Harrington et al., 1989).
We
define a roosting area as an area where mixed flocks of terns sleep at night.
These areas may be at the same location as a staging area or at a
distant location where common and roseate terns arrive at dusk or after dark,
ostensibly resting until dawn. On September 19, 1998, Peter Trimble observed a
flock of 2000 – 3000 common and roseate terns roosting at Sandy Neck,
Barnstable, on the beach, in darkness, one hour and forty minutes after
sunset.
Aerial
surveys on September 8 and 18 were flown over all study areas as well as
historically significant sites (see map).
Flights were conducted in a CESSNA 337 at 500 – 750 feet at 100 mph.
Each flight was conducted mid-afternoon.
Flocks of terns were photographed through the window using either a
Canon EOS 1-n with 300mm Canon EF lens, or Canon AE 1 Program with a Kalimar
80 – 300mm lens. Film used was Kodak 200 ISO.
Results were extremely variable, non-specific relative to mixed flocks
of terns, yet indicated important locations of staging areas. I also compiled
data and photographs on plumage changes and moult which will be analyzed and
reported on in a subsequent technical report.
This study showed large numbers of roseate terns staging and roosting around Cape Cod from August 18 until mid-September, with a rapid decline thereafter. Nisbet (1980) reported that roseate terns are not observed south of New Jersey during fall migration and concluded that they make a direct flight to the Caribbean with their oceanic route taking them east of Bermuda. Banding recoveries from the United States Fish and Wildlife Service, compiled by Trull (1979; unpublished data) show thirteen (13) banded, juvenile roseate terns arriving along the coast of Guyana, South America as early as October 2. All were trapped and eaten by local market trappers.
An observation of roseate terns on September 1, 1998, revealed over 3800 roseates roosting on South Beach, Chatham, the outermost point of land to the south and east of Cape Cod. Birds continued to flock to this roost after dark, concentrating in the largest roosting flocks in North America. We believe that although several feeding areas support abundant sand lance (ammodytae sp.) that roseate terns feed on diurnally, they flock to this remote and secure roost at night. Both locations where significant numbers of roseate terns roosted at night, Sandy Neck, Barnstable, and South Beach, Chatham, were extensive barrier spits, adjacent to deep, strong tidal flow. Conceivably the main reason for their concentrations at these locations was low disturbance; neither site had vehicular traffic. Vehicles are permitted only to a certain point on Sandy Neck. The staging and roosting terns are mainly in the vehicle- free zone. I believe this is very significant. Two diurnal staging areas which both supported flocks of more than 1000 terns of both species were Coast Guard Beach, Eastham, and Jeremy Point, Wellfleet. (Detailed observations are listed in Appendix I and Table I) Although I made three unsuccessful attempts to visit Jeremy Point, I did fly over this remote area twice, on September 8 and 18, recording flocks of 1000 and 700+ commons and roseates respectively. Both of these dynamic areas are vehicle free. Keeping pre-migratory staging and roosting areas vehicle free may be the single most important management factor in securing preserved habitats for the endangered roseate tern as well as its cousin the common tern.
Roseate
terns disperse widely from their breeding grounds in mid-to late- August, with
some leaving nesting colonies as early as mid-July.
Little is known about the movements of these birds, compared to later
nesting birds that may still be feeding chicks in a colony setting as late as
August 20. One feature related to
staging and roosting that has not been previously discussed became
clear during our study. As the
breeding season waned into mid-August at some colonies, others had been
deserted for weeks. Group
adherence (Austin 1951) plays an important role in the staging and roosting of
terns throughout the season. When
a colony is still active, late in the season, with late hatching chicks still
being tended, or territories defended within the colony area, post breeding terns stage and roost on the beaches and tidal flats adjacent
to the colony. As soon as the
colony site is abandoned, this staging and roosting area is no longer used and
both common and roseate terns move to more remote areas, usually associated
with favorable feeding sites. This
change was observed at both Monomoy Island and New Island, Eastham.
At South Beach, Chatham, on September 1, we observed a constant flight of birds arriving from the north until well after dark. These birds arrived in flocks ranging from 1-3 birds, to as many as 80-100. Interestingly, only the roseates were calling, giving the false impression that the flocks were made up largely of that species. Sub-samples of roosting birds over the observation period showed an average of 35% roseates overall. Future observers should consider that a large flock of incoming birds in dim light, offering an audio component of solely roseate “chi-vics” could be misleading. The common terns tend not to vocalize as much at this time.
The history, present status, world distribution and breeding biology of roseate terns in northeastern North America and worldwide have been widely studied (Nisbet 1980, Nisbet 1981, Nisbet 1984, Nisbet 1989, Hamilton 1981, Hays and Lima 1987, Gochfeld 1983, Trull 1988). In contrast, little is known about the behavior or ecology of roseate terns during the period between the end of the breeding season and their departure southwards toward the West Indies and South America. The main sources of information about this period are a paper by Shealer and Kress (1994) and an unpublished report by the Massachusetts Audubon Society (1994), which summarized sporadic counts of staging terns along the Massachusetts coast. In addition, scattered counts of staging terns have been published in the journal Bird Observer of Eastern Massachusetts over the years. This report has amplified the earlier information by providing systematic, weekly counts from the major known staging and roosting areas.
Between mid-August and mid-September at staging and roosting areas on Cape Cod, Massachusetts, more than 4500 roseate terns can be accounted for, as was the case on September 1, 1998. South Beach, Chatham, alone supported 3850 roseates on that day. Four sites supported significant populations of staging/roosting "large" terns, while two locations, Sandy Neck, Barnstable (n = > 600 roseates), and South Beach, Chatham, (n = 3850 roseates) proved significant staging/roosting areas. Coast Guard Beach, Eastham, was a significant staging area, with mixed flocks of terns numbering between 900 and 1700 birds on daytime counts, while all birds departed the area at dusk, flying either south or west/northwest on all count days. South Beach, Chatham, likely supported the largest staging/roosting population of roseate terns in eastern North America.
While determining the status of roseate terns on their wintering grounds is of worthwhile importance, we should not overlook the significant, indeed critical situation that exists on Cape Cod, where a single meteorological or other environmental catastrophe could affect the entire Western Hemisphere population of this graceful and buoyant seabird.
1. Adequate funding should be allocated to continue a study of the importance of staging and roosting areas, not only for pre-migratory protection, but to better understand the social/parental aspects of this part of the roseate terns’ annual cycle; also, to determine how and when known individual roseates or parent/chick groups move about at the above described sites during the 4 – 6 week period prior to migration (August 1 – September 15). We know that significant numbers of adult and fledged roseate terns use these areas; it is equally important to determine how they use them.
2. 2. The towns of Barnstable, Chatham, Eastham, and Wellfleet should pursue a program of continued systematic protection and monitoring of the roseate tern staging/roosting areas described in this paper. Nantucket Airport should be advised of the importance of Eel Point and Smith's Point as staging areas, and consider alternative flight paths from the west between August 20 and September 15.
3. Based on recommendation #2, towns should encourage and support protection of staging/roosting sites through public education, as well as define access restrictions to critical areas in each town based on this report. "Jet ski" type craft should be prohibited from the waters adjacent to the west, or inside of Coast Guard Beach, Eastham, north and west of Nauset Inlet, through the use of a buoy system, between August 20 and September 15.
Austin, O. L. 1951. Group Adherence in the Common Tern. Bird-Banding. 22: 1-15
Gochfeld, M. 1983. The roseate tern: world distribution and status of a threatened species. Biological Conservation 25: 103-125
Gochfeld, M., Burger, and I.C.T.Nisbet. 1998 Roseate Tern Sterna dougallii. In The Birds of North America, No. 370 (A. Poole and F. Gill eds.). The Birds of North America Inc., Philadelphia, PA.
Hamilton, J. 1981 Recoveries of wintering roseate terns. Journal of Field Ornithology 52:36-42
Harrington, B. A., J. P. Myers and J. S. Grear. 1989. Coastal refueling sites for global bird migrants. Coastal Zone 89: Proc.of the sixth symp. on Coastal and Ocean Manag., V.5: 4293-4307. Am. Soc. of Civil Eng., New York
Hays, H. and P. Lima. 1997 Distribution of roseate terns along the coast of Brazil. In L. R. Monteiro (ed.) Proc. of the Seventh Roseate Tern Workshop. 46pp.
Massachusetts Audubon Society, 1994. A survey and Census of Roseate Terns on their post breeding staging areas in Massachusetts from July 20 to September 21, 1994 Unpublished report to the Coastal Waterbird Program.
Nisbet, I.C.T. 1980. Status and trends of the roseate tern Sterna dougallii in North America and the Caribbean. Unpublished report, U.S. Fish and Wildlife Service, Newton Corner, MA x and 133pp.
Nisbet, I.C.T. 1981. Biological characteristics of the roseate tern, Sterna dougallii. Unpbl. report, U.S. Fish and Wildlife Service, Newton Corner, MA. viii and 112 pp.
Nisbet, I.C.T. 1984. Migration and winter quarters of North American roseate terns as shown by banding recoveries. Journal of Field Ornithology 55:1-17.
Nisbet, I.C.T. 1989. Status and biology of the northeastern population of the roseate tern Sterna dougallii: a literature survey and update: 1981-1989. Unpubl. report, U.S. Fish and Wildlife Service, Newton Corner, MA. iv and 74pp.
Shealer, D.A. and S.W. Kress. 1994 Postbreeding movements and prey selection of roseate terns at Stratton Island, Maine. Journal of Field Ornithology 65: 349-362.
Trull, P. 1988. The roseate tern in Massachusetts. Massachusetts Wildlife 38 (3):22-31
This
report would not have been possible without the help of many people. I would
like to thank Peter Borrelli, Kathy Shorr, and Robbin Peach for getting the
research project started. I thank
Dr. Ian C.T. Nisbet for guidance on the project and much useful background
material on roseate terns. Thanks also to Brian Harrington for his advice
throughout the project. I thank
my field observers; David Clapp, Peter Trimble, Jackie Sones, Blair Nikula,
Stephanie Koch, Edith Ray and Edith Andrews, and E. Vernon Laux Jr..
Gratitude goes to Dr. Richard Veit for his additional data from
Tuckernuck Island. Occasional yet timely observations at Hatches Harbor,
Provincetown, by Scott Landry answered logistical questions. Help with nasty
computer glitches was provided by Jooke Robbins, and help with manuscript
preparation, transcription of data, and data analysis was provided Carol Pearl
and Daphne Trull. Mr. Borrelli
and Dr. Nisbet made several corrections and improvements to the manuscript for
which I am very grateful. Thanks to Steve Tucker,
and the rangers at Sandy Neck for logistical support and use of their
vehicles, as well as Mr. Paul Fulcher at the Orleans Park Department for
allowing access to closed areas of Nauset Beach. John Ambrault at Ambrault Aviation Inc. is always helpful,
and flying with Chandler Lofland was wild. He accommodated my every request,
gave me some strange new perspectives, and contributed greatly to our
understanding of roseate tern movements.
For that I am grateful.
Scituate, mouth of the North River.
This site was monitored once a week over the study
period; no roseate terns were recorded here.
Sandy Neck, Barnstable.
Roseate terns were observed consistently here throughout the study period. On Aug.18, CT out numbered RT 900 to 107. On Aug 25, 1120 to 200. On Sept. 1, 674 CT to 330 RT. On Sept.8, 300 CT and124 RT were observed. A distant mixed feeding flock of 1000-1700 terns was observed. On Sept. 15, a flock of mixed terns numbering 2750 birds was estimated to be 25% RT. On the final count day, Sept. 19 mixed flocks of terns totaling 3000+ birds were estimated to be 25% RT. At 2030hrs., in the dark, a flock of 2-3 thousand roosting terns were disturbed from a roost on the beach. Daytime flyovers at approximately 2:00 PM on Sept. 8 and 18 disclosed 1200 terns and 0 terns respectively. Flight altitude was 500 ft. @ 100 mph.
Coast
Guard Beach, Eastham.
This location is a staging area, not a roosting area. On Sept. 1, 710 CT to 40 RT were counted, while on Sept. 8 a mixed flock of 1000 terns departed to the south at 1830hrs.. On Sept 10, 1500+ terns were feeding to the south along Nauset Beach until dark. On Sept 15, 595 CT and 50 RT were counted,as well as a mixed flock of 200 birds. Between 6:20 and 6:36, 6 mixed flocks totaling 216 terns were recorded flying in from the N/NE continuing west. On September 23, between 1802 and 1850hrs.(dark), 1746 common and roseate terns flew in from the southeast, heading northwest. Eighteen flocks ranging from a single tern to a flock of 500, flying high. No terns landed or were roosting on the beach. On a flyover on September 8, at ~1500hrs., I estimated 800 – 1000 terns staging on this beach. On September 18, I flew over mid-afternoon and estimated 800 – 900 terns loafing, staging on the tidal flats.
South Beach, Chatham.
This site was not visited until September 1, due to outboard engine breakdown. On that day Blair Nikula, Ian Nisbet, and Peter Trull systematically counted, estimated, and monitored the movement of common and roseate terns. We concluded that there were 11,000 common and roseate terns staging/roosting over a two-hour period, while even as darkness fell, mixed flocks were “pouring” in from the north and joining the other roosting flocks. It was a true ornithological spectacle! In the afternoon light, we made ten ratio counts of common to roseate terns. Overall, the ratio of roseates to commons was determined to be 35%, documenting a total of 3850 roseate terns at that site. One week later on September 8, we found fewer terns overall and a marked decrease in common terns. However, a total of 5706 total birds included 3538 roseate terns, an impressive 62%! A mid-afternoon flyover on September 8, revealed 300 terns, and on a repeat flyover on September 18 I counted 500-550 birds. I conclude that this site builds in numbers throughout the afternoon hours to become one of the largest and most critical roosting areas for the federally endangered roseate tern in the Western Hemisphere. As we returned by boat to the mainland on both evenings, using a flashlight to find the channel markers in the dark, the gray forms of terns and the occasional "chi-vik" call of the roseate tern was clearly evident as birds still arrived from points unknown to sleep at this remote and relatively secure location. By September 16, a different pattern had emerged. Mixed flocks of terns were flying in from the north, but continued to the northwest. Despite a flock of 200 birds on the ground, all eventually flew off to the northwest. The last recorded tern sightings at this location were on September 23 as continual flocks of terns arrived from the east and southeast, continuing to the northwest (perhaps to Sandy Neck Barnstable where 2-3 thousand terns had been roosting on September 19). A sample ratio count on this last day on South Beach revealed 30 roseates and 130 commons. By 1855 hrs. all birds from South Beach had departed to the northwest.
Monomoy Island – Monomoy National Wildlife Refuge, Chatham
The general area where common and roseate terns stage and roost on Monomoy is adjacent to the common and roseate tern nesting colony at the north end of South Monomoy Island. This is significant to the study and the chronology of the staging period here (see discussion). On August 18, an estimated 1500 terns were present with 500 roseates included. No count was done on August 25, due to inclement weather (wind). On September 1, 28 common and 45 roseate terns were present, but by the end of the count period at 1900 hrs., no birds were left on the island. One to two miles to the east and north, the South Beach observers were recording 11,000 terns at this time. For the remainder of the count period days, September 8, 15, and 22, no birds were staging or roosting on Monomoy.
Nantucket
Island
Two areas of Nantucket Island have been historic roosting and staging areas for common and roseate terns. Both are barrier spits extending westward from the west end of the island. Smith Point is the southern spit; Eel Point is the northern spit. On August 18 at Eel Point, 590 common terns and 31 roseates were counted, with a high disturbance factor. Gulls, humans, a helicopter (3 times) and general restlessness accounted for twenty-six disturbance flights in a 2-hour period. On August 25 at Smith’s Point 159 common terns and 10 roseates were counted with low numbers continuing on September 1 when 62 common and 8 roseate terns were recorded. Interestingly, the exact common / roseate ratio was recorded a week later on September 8. By September 15, no terns were observed staging or roosting, but terns were feeding offshore. On September 22, no roseate terns were observed. A mid-afternoon flyover on September 8 revealed no birds at either Smith’s or Eel Point, while a flyover on the September 18 revealed 200-300 birds on Eel Point.
Tuckernuck Island
Although this was not a funded study site, Dr. Richard Veit maintains a research station on the island and was kind enough to supply counts of common and roseate terns for our study purposes. Dr. Veit recorded numbers of terns and shorebirds throughout the period, but I have chosen only the numbers that correspond with the simultaneous study dates. On August 20, 300 roseate terns were recorded. On August 26th, 500 roseates were recorded. September 2 revealed 300 roseate terns, while on September 8, 300 roseates were recorded. The 300 roseate tern count was consistent between August 29 and September 12, then dropped precipitously to 25 roseates on September 14. Roseate tern numbers rose slightly and erratically until September 19 with a high of 100 birds, then fell off to 25 roseates on September 22.
Martha's Vineyard
E. Vernon Laux prefaces his report by suggesting that 1998 recorded the earliest departure date for common and roseate terns from the waters of Martha’s Vineyard in 20 years. On August 18, 106 common terns and 220 roseate terns were present at Eel Pond, Edgartown. On the same day at Katama, 142 common and 107 roseates were observed. On Aug 25, at Eel Pond 59 common terns and 31 roseates were observed. No numbers of terns were observed on Martha’s Vineyard after this date.
During the study period, disturbance was quantified at each watch. In some cases, length of disturbance was also recorded. As suggested in the report, roosting and staging areas tend to be in remote areas where the degree of disturbance may be minimal, and it was. The most frequently recorded flock movements were due to the general uneasy, skittish, character of the flocks. Often while counting or observing from a distance of 60-100 meters we observed the birds casually rise, circle for less than one minute, and land again. During these periods of capricious behavior, the flock might divide and separate, making data collection difficult. In some cases, flocks may have numbered up to 1000 birds of different species and ages. There were no visible or obvious stimuli for these brief flights. Although observers recorded 35 – 50 of these “disturbed” flights, I would suggest many more. On September 8, at South Beach, Chatham, at 6:50 PM, two Parasitic Jaegers (Stercorarius parasiticus) flew 10 meters directly over a flock of 200 roosting terns and caused no disturbance. Herring Gulls (Larus argentatus) caused 12 occurrences of disturbance either flying over flocks of terns or walking inadvertently too close to the flock, while Great Black-backed Gulls (Larus marinus) disturbed the terns only 3 times. Instances of people, beach walkers, disturbed flocks of terns 7 times, our observers 2 times, shellfishermen 2 times, low flying airplanes and helicopters (Nantucket) disturbed flocks of terns 4 and 3 times respectively. One flight path for incoming aircraft to Nantucket airport from west to east occurred over Smith Point. Six instances of automobile disturbance (2 on Martha’s Vineyard, 4 on Nantucket) and three instances of boat disturbance (1 kayaker, 1 small motorboat at Coast Guard Beach, and 1 motorboat off Monomoy) were recorded. A low degree of incidental animal disturbance occurred throughout the study period; two instances of Belted Kingfisher (Megaceryle alcyon) flushing the birds on Nantucket were reported as were two disturbances by Northern Harrier (Circus cyaneus). A harrier killed a juvenile common tern at 6:25 PM on August 18. Only one incidence of disturbance by a dog was recorded; it occurred on Coast Guard Beach, Eastham.