Massachusetts Tern Inventory 2000
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Massachusetts Tern Inventory 2000 Bradford G. Blodget, State Ornithologist Overview The year 2000 was a challenging one for terns in Massachusetts. Long-term fundamental problems confronting terns asserted themselves during the 2000 season. The diabolical problems of predation and lack of suitable colony site alternatives work in concert to limit tern numbers and to threaten recovery and long-term stability of tern populations in Massachusetts. For the second year in a row, fox activity precluded nesting at Plymouth Beach. Although some 1,000 pairs of Common Terns appeared early in the season, they quickly abandoned the site. Presumably many relocated to the immense colony at Monomoy-South, Chatham. Nesting at New Island in Eastham/Orleans was unproductive on account of Great Horned Owl predation. Another chronically unproductive site usually beset with owl problems, Gray’s Beach, Yarmouth, reportedly experienced some production this year. Despite these trouble spots, 81% of all the Common Terns in the state, which were concentrated at three sites-- Monomoy-South in Chatham, Ram Island in Mattapoisett and Bird Island in Marion-- experienced good to excellent productivity. Weather conditions during the season were generally benign, except for an unseasonable northeast storm that struck on 6 June, washing out some nests, particularly those of Least Terns at exposed sites. During the 2000 season, nesting terns were reported from 67 sites out of the aggregate total of 114 sites reported active in at least one year from 1970 to the present. Common Tern numbers declined 6% to 13,340 pairs, reversing seven consecutive years of increase. Roseate Tern numbers, however, increased 17% to 2,124 pairs, marking the first time their numbers have ventured above the 2,000 pair level since 2,023 were estimated in 1979. Since 1970, the highest Roseate Tern estimate was 2,300 pairs in 1972. Least Tern numbers were estimated at 3,276 pairs, down 4% from the year-earlier level. Laughing Gull numbers grew 36% to 1,097 pairs, the first time their numbers have surpassed the 1,000 pair mark since 1991. Agencies in the cooperative monitoring network continue to be engaged in a number of large projects. The U.S. Fish & Wildlife Service’s Avian Diversity Program at Monomoy National Wildlife Refuge entered its fifth year in 2000. While Common Tern numbers there have soared, 2 Roseate Tern numbers have not responded as well as expected (actually declining to three pairs from 27 in 1999). Superlative nesting habitat at Ram Island, Mattapoisett, along with social factors, may have drawn birds from other sites, including Monomoy. In addition, habitat conditions for Roseate Terns may not be optimal at Monomoy. If the Monomoy Common Tern colony holds together long enough, conditions there—such as dense vegetative cover—may gradually develop and become more attractive to Roseate Terns. In the meantime, Common Terns produced at Monomoy should recolonize and foster growth at new sites, including those where aggressive Common and Roseate Tern restoration efforts are underway. Two of these sites include MassWildlife’s project at Penikese Island, Gosnold (initiated in 1998 after pilot work in 1995) and a new project begun this year at Muskeget Island, Nantucket by The Nature Conservancy, with additional funding support from the Blake Fund and other private sources. General Methodology Censusing of terns in Massachusetts is accomplished using “pairs” as the basic census unit. Generally, complete nest counts are made, at some sites corrected using the Lincoln Index. At a few sites, pair estimates may be extrapolations based on partial nest counts or adult estimates adjusted to pairs by multiplying by 0.8. Where nest counts are made, only nests with eggs are counted and the number of nests is converted to pairs on a 1:1 ratio. Estimates of the number of pairs reported and discussed in this summary, unless otherwise noted, are “A-period” estimates made during a standard 5-20 June window. “B-period” estimates, as sometimes referenced herein, are estimates made later than the “A-period” counts and not included in the total pair estimates for the state. Common Tern Common Tern numbers, after seven consecutive yearly increases, declined in 2000 to 13,340 pairs at 32 sites. The drop amounted to about 6%, essentially erasing the previous year’s increase. Terns attempted to recolonize Plymouth Beach, but quickly aborted when faced with fox predation. Most of the Common Tern nesting activity northward from Plymouth to the New Hampshire state line continued to be at marginal sites such as flood-prone salt marshes and dilapidated piers and pilings. Portions of the old Central Square Piers in East Boston collapsed in 2000, taking some nests down with it. While there was reportedly some productivity at Gray’s Beach, Yarmouth, the colony at New Island, Eastham/Orleans was—as usual—severely disrupted by Great Horned Owls and there was little or no productivity. At the Monomoy Islands, Chatham, numbers increased to 6,897 from 5,536 a year earlier, a 26% increase (on top of a 134% increase in 1999). Monomoy National Wildlife Refuge now harbors about half (51.7%) the Common Terns in Massachusetts. Other sites harboring 1,000 pairs included Ram Island, Mattapoisett (2,030 pairs) and Bird Island, Marion (1,880 pairs). Eighty-one percent of nesting Common Terns were concentrated in these three sites and experienced good to excellent productivity. The total number of active Common Tern sites dropped to 32 from 34 in 1999. 3 Six additional sites reporting 100 pairs included New Island, Eastham/Orleans (997 vs. 2,176 in 1999), Gray’s Beach, Yarmouth (684 vs. 953), Haystack Point at the Edgartown end of Sengekontacket Pond (140 vs. 160), Penikese Island, Gosnold (126 vs. 101), Woodbridge Island, Newburyport (120 vs. 240), and Central Square Piers, East Boston (114 vs. 176). Note that all these sites except for Penikese registered declines. Least Tern The estimated Least Tern population declined 4% to 3,267 pairs in 2000 from last season’s record high of 3,416 pairs. This still goes into the records as our second best year since careful record keeping began in 1970. Given the unstable nature of Least Tern colonies and the difficulty censusing them accurately, the decline is likely within the margin of censusing error. From 1997 onward, estimates have held above the 3,000 pair level. This year’s results reflect continued ideal habitat conditions offset by predation at some sites and a northeast storm on 6 June that washed-out nests at some sites. The largest colony in 2000 developed, as in 1999, at Dunbar Point (Kalmus), Barnstable, where 817 pairs were estimated. Nine additional sites reported estimates of 100 pairs in 2000 (vs. seven in 1999) including Dead Neck-Sampson’s Island, Barnstable (383 pairs vs. 87 in 1999), Little Beach, Edgartown (237 vs. 0), Crane Beach, Ipswich (220 vs. 220), Barney’s Joy— Little Beach, Dartmouth (138 vs. 61), North River mouth, Scituate (133 vs. 44), Sandy Neck, Barnstable (128 vs. 148), Monomoy-South, Chatham (119 vs. 103), Tuckernuck Island, Nantucket (110 vs. 75), and Great Island, Wellfleet (105 vs. 83). Note that seven out of these nine additional sites carried substantially more pairs than in 1999 and one site had the same number of pairs as in the previous year, reflecting a generally broader distribution of birds among sites in 2000 compared with 1999. Also indicative of this pattern, Least Tern nesting activity was reported from 50 sites this year, up from 44 a year ago. Roseate Tern The estimated Roseate Tern population increased to 2,124 pairs in 2000, up 17% from 1,810 pairs last season. This marks the first time that estimated roseate numbers have risen above the 2,000 pair level since 1979 (2,023 pairs). Since 1970, the highest Roseate Tern numbers were recorded in 1972 (2,300 pairs). This season’s strong performance was fueled almost exclusively by dramatic increase (57%) at Ram Island, Mattapoisett where numbers rose to 998 pairs from 630 pairs in 1999. This increase may be attributable to the fact that no winter storms overwashed the island during the winter season. As a result, lush vegetation—ideal for roseate nesting—developed. In addition to ideal nesting cover, the strong numbers were likely also driven by other factors including the absence of any serious predation threats and natural recruitment within the Northeastern population. Also, the possibility that last year’s numbers were underestimated to some degree cannot be ruled out. Unfortunately, the good news on numbers of pairs was offset by less encouraging progress on other parameters. Essentially 100% of the Roseate Tern pairs this year were concentrated at only two sites—Bird Island, Marion (1,130) and Ram Island, Mattapoisett (988). 4 On outer Cape Cod, only an additional six pairs could be located---three at Monomoy-South, Chatham and three at Nauset-New Island, Eastham/Orleans. Thus there were only four stations with nesting Roseate Terns, down from six in 1999; this is the poorest showing since 1986. Plymouth Beach, long a small but steady roseate station, was abandoned in 1999 on account of fox predation. Restoration efforts at Penikese brought stronger numbers of Common Terns to the site in 2000, but, while Roseate Terns frequented the site, none nested. At Monomoy-South, numbers actually fell to three pairs this year from 27 a year earlier, despite explosive growth in the numbers of Common Terns there. And at Muskeget Island, no nesting roseates appeared this year despite last season’s five pioneering pairs. But on a positive note, efforts are underway to remedy the fox problems at Plymouth and the difficulties there will eventually be resolved.