See also Maury's supplement to this material in What do the changes mean? (February 2002).
Unlike midwinter TASL censuses, November counts give a snapshot of populations of migratory waterfowl visiting the Harbor. For most species populations dwindle as November's cold rains turn to December's first snows. Our data indicates that a few species (Common Eider, Brant, Bufflehead, American Black Duck, Sanderling and Purple Sandpiper) have reached or are close to reaching their overwintering populations by November, while several others (Common Goldeneye, Greater Scaup, Canada Goose) continue to build their populations throughout December and early January.
November censuses have been conducted from 1980 to 1983 and
again from 1988 to 1997 (including one December count, in 1989). Table 1 provides information on
conditions that may have impacted either the timing of migratory
activity or the completeness of the individual TASL counts. To
address the former I have listed the departure from average Boston
temperature for each October and November. This provides a rough
indicator of weather factors that may have delayed or speeded
up the migration.
normal October temperatures—°F | normal November temperatures—°F | Factors affecting count | |
| 11/23/80 | Missing some current sites | ||
| 11/29/81 | Missing some current sites, very rough seas | ||
| 11/13/82 | Missing some current sites. heavy rain, Hull and Weymouth not done | ||
| 11/19/83 | Missing some current sites | ||
| 11/13/88 | Nahant and 75% of Hull not done | ||
| 12/10/89 | No access to Deer Island | ||
| 11/18/90 | No access to Deer Island, rough seas | ||
| 11/24/91 | Drizzle, rough seas, 85% of Hull not done | ||
| 11/22/92 | |||
| 11/14/93 | |||
| 11/20/94 | Rough seas | ||
| 11/19/95 | |||
| 11/24/96 | |||
| 11/16/97 |
Table 1:
Weather, sea, and observer factors affecting Boston Harbor
early winter TASL counts
Also in Table 1 are listed factors that may have limited our ability to attain complete counts in the harbor. Some are obvious: for example, some areas received no or only partial coverage. During the first four years of TASL counts certain locations (Reserve Channel in South Boston, Malibu Lagoon in Dorchester, Long Island and parts of Town Cove in Quincy, the mouth of Back River in Weymouth, and Strait's Pond in Hingham/Hull) were not included in the counts, as they are now. Not including these sites decreased the counts of many species by 5 to 8%. Lack of access to Deer Island in 1989 and '90 may have dramatically affected counts of eider and Bonaparte's Gull. Since Hull often reports a disproportionately high number of species and individuals, the 1982, '88, and '91 counts are low by at least 15 to 20% because Hull was not completely censused. Likewise in 1982 and 1988 Weymouth and Nahant respectively were not counted, affecting the count by 10 to 15%.
Bad weather also hampers our ability to make good counts. Heavy rains in 1982 contributed to the very low counts for many species. Likewise strong winds which cause rough seas (1981, 1990, 1991, 1994) limit the observers' ability to find small water birds (e. g., grebes, Bufflehead) or birds often found individually or in small groups (goldeneye, loons). Rough seas also make it harder to get accurate counts of congregating birds such as eider, scoter, Bufflehead, scaup, or mergansers). It is not unreasonable to suppose that very rough seas will drop counts by at least 10%, moderately rough seas by at least 5%, and heavy rains by at least 10%.
In Table 2 I provide the year-to year counts of selected species, their long-term averages, and the total number of water bird species (i. e., loons, grebes, cormorants, ducks, geese, shorebirds, waders, alcids, and specialty gulls) observed on each date.
On average, 33 species have been identified on a given census. The high was 39 species in 1983 and the low was 28 in 1982 and 1988, when two of the seven areas were not covered.
The total number of species observed in November 1997 was on the high end of the historical range. The 38 species is somewhat inflated since 7 species were represented by only one individual (King Eider, Harlequin Duck, Northern Gannet, Black Guillemot, American Coot, Iceland Gull, Ruddy Turnstone).
During the past two November counts the numbers of several species, including Cormorants, Brant, American Black Duck, Greater Scaup, Bufflehead, goldeneye, Red-breasted merganser, Bonapartes Gull, Sanderling, Purple Sandpiper, and Dunlin have all been lower than the long-term averages for these species; in fact, the 1996 or 1997 count totals for these species were at or near a record low. The Brant and black duck decreases are the most notable since we have historically seen relatively stable numbers. These low numbers are particularly significant given the good field conditions and complete area coverage in both years. This contrasts with the less favorable conditions and incomplete counts seen in the 1980's, especially the 1982 census when maybe only 50% of the birds in the Harbor were counted (see Table 1).
The decreases are not likely linked to anything happening in Boston Harbor. Since we are essentially getting a snapshot of migratory patterns, the decreases, if they are real and not just a statistical anomaly, are due to some bigger pattern. I believe the weather data provided in Table 1 may speak to this bigger picture. Average monthly temperature in Boston was well below average in each of the last three Novembers, and last 2 Octobers. The November 1996 departure was the largest of any of November counts: fully 5 degrees below average. 1997 ranked third coldest and 1995 fourth coldest. For all of the species showing recent low numbers Boston is in the northern third of their wintering range. One might expect that cold weather during the migration period would drive birds farther south in their wintering range.
Interestingly, Common Eider have shown above average concentrations in 1996 and 1997. Boston is closer to the southern end of their wintering range. Therefore, if weather factors are driving birds toward the southern parts of their ranges, we would have expected to see more eider. And we did! Scoter numbers were at record high numbers in 1997. They tend to winter farther north than some of the migratory waterfowl (e.g. Red-breasted Merganser, Brant, Bufflehead, goldeneye). Could their high numbers be due to the colder autumns? This seems like an interestingly research topic.
Several other species showed above average numbers in 1997. Canada Goose numbers were at a record high, grebes were plentiful but not near past highs, and loons continued their apparent increases over 1980s levels.
Over the past couple of years I have heard/read several comments regarding a region wide-increase in loons. Part of this is apparently due to better protection of common loon nesting sites in the northeast and the placement of artificial nesting rafts in Massachusetts (and other states?). These actions are increasing the reproduction and fledgling survival rate. Our data show a modest increase in Common Loons. However, Red- throated Loons now appear in consistently high numbers in our fall surveys. Whereas in the early eighties Common and Red-throated Loons tended to be seen in approximately equal numbers, over the past sevaral years the Red-throated account for over two-thirds of the totals (in 1997 they accounted for 75% of the total).
One final note on Common Loons. Research over the past several years has indicated that there is a five-fold increase in mercury concentrations in loon body tissue as you move from west to east (i.e., Alaska to the Canadian Maritime Provinces). This is believed to be caused by atmospheric transport of mercury emanating from coal-fired (coal has minute traces of mercury) energy sources and and waste incinerators (they burn batteries and fluorescent bulbs which contain mercury). Since the jet stream moves west to east, mercury is presumably transported from the west and especially the mid- west and deposited in the northeast with rain and snow. Lakes where loons nest concentrate mercury deposited over an entire watershed. Mercury tends to bioaccumulate in tissue and is biomagnified up the food chain. It is a powerful neurotoxin. Loons are seen as a sentinel species for mercury poisoning. The increasesof mercury in loon body tissue have not as yet been associated with any impact on loon populations, but scientists are concerned.
Another interesting trend which our data has uncovered is the distribution of Common Eider in the Harbor. Anecdotal comments from the mid-70s suggested that large eider concentrations were historically seen in the outer reaches of Wollaston Bay. Yet TASL data beginning in 1980 showed eider mainly seen off Deer Island in Winthrop with a smaller raft seen from Allerton Point in Hull. Beginning in 1992 (and extending to the present) the huge rafts off Deer Island have often been greatly diminished. At the same time eider began to be seen throughout the Harbor, but especially in a cresent extending from Hull and Higham bays up to Nut Island in Quincy, and extending north to Long Island.
The abrupt change suggests that there is a story to be told. Two major things occured in Boston Harbor in late 1991 that had the possibility of creating changes in eider distributions. The first was the cessation of sludge deposition in the Harbor (off Deer and Long I.) in December 1991. We now have reasonably strong anecdotal data suggesting that animals like flounder and lobster, which were dependent on the organic enrichment provided by the sludge, decreased in and around Deer Island, partially as a result of the cessation (see Worms, fish, birds, mammals and the Harbor clean-up). However, eider eat mussels. If anything, mussels should benefit from the cessation of sludge discharge (no sludge to bury them). Therefore, eider around Deer Island should also benefit, or see no impact. Meanwhile the effect of the sludge discharge was generally a very localized impact. Mussel beds (and eider feeding on them) in Quincy should not have been effected. Therefore, it seems unlikely that the change in eider distribution had anything to do with sludge.
The other event that took place was a surprise nor'easter, the Halloween Storm of 1991. This event created the greatest storm surge in Boston of anything since the Blizzard of 1978. MWRA sediment data in the Harbor show major changes in the bottom sediments of the Harbor in the spring oof 1992 as compared to the late summer of 1991. Presumably, this was due to the large scale resuspension and movement of sediment as a result of this storm. I believe that it is likely that some of the mussel beds off Deer Island were either buried or torn up as a result of the storm, providing less food for eider. Interestingly, as noted earlier, prior to the 1978 blizzard, eider were presumably seen in large numbers in outer Wollaston Bay. No solid data exists to document changes in the sediments as a result of that storm, but lobsterman have told me that they believe mussel beds were buried under several feet of resuspended sand and silt. No more mussels: no more eider. Did the 1991 storm in anyway enhance the mussel beds in Hull-Hingham-Quincy- Weymouth? We don't know. However, it does seem likely that the October 1991 storm had some impact on the ability of eider to make a living in Boston Harbor.
LOONS: Most November birds are Red-throated. These fish eaters appear to be more numerous over the past several years. They are mainly found on the ocean side of Nahant, Winthrop, and Hull.
GREBES: Most are Horned. A small number of Red-necked are commonly seen off Winthrop Beach. Fall populations have generally been stable but variable since the early '80s Sizable numbers are usually found off Wollaston Beach and Hough's Neck in Quincy and off World's End in Hingham and Hull. Their winter diet consists of small fish and crustaceans.
CORMORANTS: In Table 2 Double-crested and Great Cormorants are lumped together. While there is no clear trend in total cormorant numbers, the proportion of Greats has decreased from over 90% of the total in the early '80s to 25 to 30% more recently. The midwinter data provides a clearer indication of the steep decline in Greats. (This issue will be dealt with in a later article.) The flip side is that Double-cresteds have shown a modest increase over the past several years. Both are fish-eaters, with Greats being found off the Harbor islands north and west of Hull and the Double-cresteds found mainly in the inner Harbor and Dorchester Bay.
GREAT BLUE HERON: Large increase in the late '80s and '90s over the early '80s. Most of the increase is unexplained; some may coincide with our access to Logan Airport between 1988 and 1994, where a substantial number roost in adjacent marshes.
BRANT: Extremely stable populations over the past 16 years. Low counts occurred during years of incomplete coverage. Brant feed mainly on eelgrass. Over the past fifty years Brant populations have declined on the East Coast due to the loss of eelgrass beds to a wasting disease. Ironically, in Boston they are never found around the eelgrass in Hingham. Brant also like sea lettuce, a submerged green leafy plant which grows well in the high nutrient waters of Boston Harbor. Highest concentrations of Brant occur around Squantum and Hough's Neck in Quincy and around the airport in East Boston. Once the Deer and Nut Island wastewater discharges cease in 1997 or '98 the major source of nutrients to the Harbor will be eliminated. Will this affect the sea lettuce beds and the Brant? We'll see in a few years.
CANADA GOOSE: Our data is consistent with other studies which show an increase in the overwintering population in southern New England. This is apparently due to the artificial feeding of these parkland visitors.
AMERICAN BLACK DUCK: Very stable population with little variability. Highest densities in sheltered mud flats around the Harbor. They feed on mud snails and vegetation.
GREATER SCAUP: The high variability in population partially masks the downward trend which is more evident in the midwinter data. Scaup populations are declining throughout the east, presumably due to heavy metal (e. g., lead, copper, nickel, zinc) contamination. (See Scaupnet) Scaup are generally found in flocks of 50 to 250 birds around Snake Island in Winthrop Bay, at the mouth of the Weir River in Hull, in western Wollaston Bay or at the mouth of the Fore River in Weymouth. They tend to feed on mussels and other mollusks.
COMMON EIDER: The most abundant species in the Harbor, with close to 5000 seen in the average year. In November they are found in the highest densities around mussel beds off Deer Island in Winthrop, on the north shore of Hull, and off Nahant. Their populations have been stable but variable with all but one of the lowest counts occurring when either Deer Island, Hull, or Nahant were not censused. The low count of only 264 in 1993 came on a relatively early (November 14) and unseasonably mild (71° F) TASL census. Presumably, the main eider movement had not yet occurred.
SCOTER: All three scoter species are grouped together since there are numerous reports of mixed flocks of scoter spp. (i. e., birds too far away to identify to species). The majority (80%+) are White-winged Scoters with most of the rest Surf. While White-winged populations have been stable, Surf populations have risen sharply over the past several years. Both species feed on mussel beds and are found in highest densities on the ocean sides of Revere, Winthrop, and Hull and in northern Wollaston Bay.
COMMON GOLDENEYE: Found in highly variable numbers with no discernible trend. Their variability is mainly due to their late migration and is probably somewhat weather dependent. They are found uniformly throughout the Harbor and feed on mussels and small crustaceans.
BUFFLEHEAD: Very stable population found in highest density in and around Hingham Harbor and the Weir River estuary in Hull/Hingham. They have a varied diet of crustaceans, mollusks, fish, and aquatic vegetation. Their high density in Hingham Harbor may be related to the occurrence of the last remaining eelgrass bed in Boston Harbor found at the mouth of Hingham Harbor. Besides being a good source of food, eelgrass beds provide an important nursery for fish and crustacean populations. In recent years the size of the bed has been decreasing, and coincidentally the Bufflehead have tended to be found farther up into Hingham Harbor rather than at its mouth. Are these observations linked?
RED-BREASTED MERGANSER: The population of these fish eaters has also remained stable, but less variable than that of the eider. Like eider, low counts can be attributed to incomplete coverage. In November mergansers are found throughout the Harbor; but routinely the highest concentrations occur around Thompson Island in Dorchester Bay (500 to as many as 1500) and at the mouth to Hingham Harbor (several hundred).
SHOREBIRDS: Black-bellied Plover numbers show no trends since the 1980s. Sanderlings have shown a definite increase during the '90s while Dunlin and especially Purple Sandpipers have apparently been decreasing. The vast majority of Sanderling and Dunlin are found along Revere and Winthrop beaches, while the Purple Sandpipers are on the rocks along Nahant or on the Five Sisters off Winthrop Beach. The plovers are more commonly found in the marshes and mud flats in Quincy.
BONAPARTE'S GULL: Steadily increasing since the early 1980s. Most birds are found around the effluent discharge off Deer Island. Their diet is reputed to be mainly insects and small fish. It is unclear whether the birds off Deer Island are feeding on invertebrates/fish drawn to the discharge or are scavenging on the organic matter discharged. Their close relative, the Common Black-headed Gull is a scavenger on garbage dumps and wastewater effluents in Europe. During the early '80s only a single black-headed gull was reported on November counts. More recently several of these rare birds are reliably found. The numbers of these two species could be reduced once the Deer Island discharge ceases in 1997 or '98.
HARBOR SEAL: Sightings increased in the late 1980s and have leveled off since. This trend is identical to that reported by the New England Aquarium for the breeding population in the Gulf of Maine and the wintering population in southern New England. Seals in the Gulf of Maine were decimated by an influenza epidemic in the '70s to early '80s. The sharp population increase during the '80s was a normal rebound.
A mixed flock of 1000 to 3000 goldeneyes, mergansers, Buffleheads, scoters and grebes roosts off the old bath house on Carson Beach (Dorchester Bay) every night. It appears that most of the birds in Dorchester Bay and northern Quincy Bay move in during the half-hour before dark. It is quite a sight. (See The big roost)
Likewise, most of the Red-breasted Mergansers in Hull, Hingham and Weymouth appear to fly north past Deer Island late in the afternoon to roost off Revere Beach. Eider in Hingham and Hull Bays fly out of the Harbor at dusk to join the larger flocks off the Harbor islands. Both species can be observed moving through Hull Gut (Pemberton Point).
Maury Hall
TASL News Winter 1996
Updated 1/98
Maury is a wildlife biologist and specialist in benthic research for Massachusetts Water Resources Authority. He is co-organizer of Boston Harbor TASL Censuses and is in charge of analyzing and compiling the data.
This summary article was sponsored by a grant from the Charles Blake Fund of the Nuttall Ornithological Club.
last updated: 1/17/1998
url: http://www.gis.net/~szendeh/tnovsum.htm