The federally and state threatened Piping Plover generally prefers nesting in sparsely vegetated areas from the ocean side berm to the bay or pond shore, including areas in blowouts, the back dune and on sand spits. The natural processes of wind and wave erosion help maintain existing nesting areas and create new ones. Each year, monitors search for nesting pairs at traditional sites and also newly established sites. Of the approximately 25 nesting sites used within the past decade, most are still in use. No new sites were established in 2000.

The first Piping Plovers arrived in early to mid-March. The first completed nests in 2000 were found on April 26-27 (at Tashmoo West and State Beach). Since both were found with completed clutches, the first egg was probably laid on April 20 or earlier. This is similar to early nesting dates from other years (see previous reports, Swanson 1999-1997). This year the first nests hatched around May 26 (at Lucy Vincent Beach, Black Point Pond, Tashmoo West and State Beach) and the last on July 25 (Dogfish Bar and Sylvia State Beach).

The number of active nests reached a peak during the first week of June. A sharp drop in number of active nests occurred following the June 6 nor'easter, when one quarter of the active nests were washed out. A small peak during mid-June represents renests. However, 5 of 7 pairs that lost nests during the storm did not renest.

In 2000, the number of breeding pairs increased slightly, following a sharp decline over the last three years. The increase may be a result of a slight increase in reproductive success in 1998 and

1999. Forty-five pairs were recorded this year, a small increase from the 1999 breeding population of 42 pairs, but still a 21.1% decline from the peak breeding population of 57 pairs in 1995 and 1996. The overall decline over the past three years may be a response to lowered reproductive success since 1994's high of 1.86 fledglings per pair.

This season only 38 plover chicks fledged from 45 pairs. Their reproductive rate of 0.84 fledglings/pair is the lowest since 1990 and is less than half of 1994's rate of 1.86 fledglings per pair. Since 1996, reproductive success has been below the 1.24 fledglings per pair thought necessary to maintain a stationary population over the short term (U.S. Fish and Wildlife Service, 1996, p. 24).

The plovers' reproductive success is a result of both hatching and fledging success. In 2000, success was greatly affected by poor weather conditions, especially the June 6 nor'easter.

Fledging success (the percent of chicks fledged per hatched egg) was the lowest of the last eight years. Cold, rainy, and windy weather most likely increased mortality of very young chicks. In addition, predation of chicks was high at some usually highly successful sites such as Tashmoo West and Mink Meadows. While predation was not observed directly by staff, at both sites crows

were seen frequenting areas where the chicks usually fed and in one case a beach guard reported seeing a crow take at least one chick.

On the other hand, hatching success (the percent of eggs laid that successfully hatched) increased to 62.8% from a low of 50.8% in 1999. The figure below compares egg loss from all causes from 1993 through 2000. In 2000, flooding was the cause of loss of 13.1% of all eggs laid. (Only two of the seven pairs that lost nests to flooding renested.) In previous years, loss to flooding averaged only 1.3%. However, overall hatching success increased from 1999 due to fewer abandonments (14.1% vs. 28.8%). Egg loss due to hatching failure and unknown causes continues to remain low. Predation also declined from 1999 levels (from 8.0% to 13.6%) and was only an important factor for unexclosed nests.

The next two figures look at the effect of exclosures on egg loss due to predation and abandonment. Overall, egg predation rates showed no clear trend over the period 1993 to 2000. Predation on

unexclosed eggs averaged 71.0% while predation of exclosed eggs has remained low in all years (averaging 4.0% of all exclosed eggs). Exclosures have been, and still are, extremely effective in reducing predation on eggs. (Since the number of unexclosed eggs each year is small relative to exclosed eggs, any nest that hatches without an exclosure can cause a seemingly large decrease in predation rates (as in 1995, 1999 and 2000).

Egg loss due to abandonment declined again in 2000, following a sharp increase in 1999. The abandonment of unexclosed eggs has been below 5% in all but 1993 and 2000. From 1993 to 1996, abandonments of exclosed eggs also averaged 4.5%. However, from 1997 to 2000, abandonments of exclosed eggs averaged 19.5%, quadrupling the rate of the previous four years. In 1999, nearly one third (32.9%) of all exclosed eggs were abandoned. In 2000, the abandonment rate of exclosed and unexclosed nests was about equal (14.2% and 13.3%, respectively).

The cause of the increase in abandonments of exclosed nests is unclear and brings into question the efficacy of using exclosures at sites where the abandonment rate has been high. One prominent theory is that predators, such as crows, hawks, or skunks have now learned that eggs are inside the exclosures. Persistent harassment by these predators may cause the birds to abandon. Of even more concern, in recent years adult birds have been killed in or near exclosures, possibly by predators cued in to the exclosure.

In the last two years, large numbers of abandonments have occurred at 4 sites, Squibnocket Beach, Long Beach, Norton Point Beach, and Long Point Wildlife Refuge. On Squibnocket and Long Beaches in 1999 and 2000, a total of eight complete clutches were abandoned in mid-May, soon after they were exclosed. Since the cause(s) of the abandonments were unknown, the renests were not exclosed out of concern that predator harassment may have been the cause. Only three of the eight pairs renested, but two successfully fledged young from unexclosed nests. On Norton Point Beach, following five nest abandonments in 1999, including the loss of 2 adult birds (probably related to the exclosures), the decision was also made to not exclose late nesting birds. Neither of the two late nests intentionally left unexclosed successfully hatched; one was depredated four days after completion of the clutch and the other before the clutch was completed.

In 1999, Long Point Wildlife Refuge had two nests abandoned about a week prior to their estimated hatching date. The abandonments may have been caused by harassment from a nearby nesting Northern Harrier pair. A third nest in the same location successfully hatched, however all four chicks were gone within a couple a days, lending support to the predator theory. However, the nests, located along the pond shore, were subject to rising water level and possible inundation within another week or two, offering an alternative, although less likely, explanation for the two abandonments.

At most sites, however, exclosures continue to be extremely effective in protecting eggs throughout incubation. Even in 1999 with its high nest abandonment rate, only 32.3% of unexclosed eggs hatched, while 53.7% of exclosed eggs

hatched. Most sites had no nest abandonments of exclosed eggs. Exclosures should continue to be used at beaches that have not experienced high rates of nest abandonment.

Statewide preliminary data indicate that the Piping Plover population showed a slight increase, with an estimated breeding population in 2000 of 503 pairs. However, the estimated reproductive success of 1.07 chicks per pair is the lowest since the state started collecting this data in 1990 (Hecht, 2000). Vineyard organizations monitored 8.9% of the state population in 2000.

Least Terns typically nest on relatively flat and unvegetated beaches, habitat that is continuously altered by storms. Changing habitat due to storms and overwash and the effects of predation often result in cycles of abandonment and establishment of new colony sites during the breeding season, and over the course of years. Therefore, each season monitors must regularly visit known colony sites, but also search for newly established sites. Of the 18 sites used over the past decade, only seven were active in 2000. SMF monitors 11 of the historic sites, of which four were active in 2000.

A count of nesting Least Terns on the Island during the census window (June 5-20, the "A Count") found a total of 349 nesting pairs at 7 colonies (Table 4). Census numbers since 1990 show that the Least Tern population on the Island is continually fluctuating with a mean of 295 breeding pairs.

Most of the birds this year nested in one large colony at Little Beach in Edgartown (237 pairs during the census). Predator fencing was placed across the spit to prevent entry of ground predators. The colony grew to about 350 pairs by early July. At that time, about 800 terns, including adults and chicks, were counted in the colony. Estimated reproductive success there was very high. Eastville Beach again had a good size colony of 65 pairs during the census, after suffering from rat predation in 1999. The remaining colonies had fewer than 20 pair each, with moderate to poor productivity. The reproductive success for each colony is only roughly estimated, since fledglings often hide in nearby vegetation and are difficult to count.

Statewide preliminary results showed a slight decrease in the estimated number of Least Terns in 2000 from 3,416 breeding pairs (state record in 1999) to 3,267. Vineyard organizations monitored and protected 349 pairs (or 10.7% of the statewide population).

In 2000, only one Common Tern colony was again found on the Vineyard (at Haystack Island, Sengekontacket Pond) (Table 5). After reaching highs of 300 and 260 breeding pairs in 1997 and 1998, respectively, the population dropped again in 2000 to 140 pairs. Even though the population has declined over the last 3 years, it still compares favorably with the average population size for the years 1990 to 1996 of 117 breeding pairs.

High tides and possibly predation from gulls may be the cause of lowered success over the last few years. In 1999, for the first time, a Great Black-backed Gull nest (with ~two week old chicks) was found at the north end of the island during the first census visit. In previous years, gull predation on young tern chicks had also been observed. This year, a visit in mid-May found a three egg Great Black-backed Gull nest and the eggs were removed with permission of the island manager. Subsequent visits found no further gull nests, suggesting that the pair did not attempt to renest. Such gull management should be continued each year to prevent the establishment of a gull colony in future years.

The declining population at this one island colony points strongly towards establishing a new, second colony on the Vineyard, either at a formerly used site (Edy's Island, Menemsha) or at some new site with potentially suitable habitat (such as Little Beach, Edgartown).

Statewide, Common Terns numbers also declined slightly in 2000 (with an estimated 13,344 breeding pairs), from the 1999 population of 13,979 (the highest number since the start of record keeping in 1970). Breeding birds on the Vineyard represented only 1.0% of the statewide population.

American Oystercatchers were not completely censused in 2000. However, data that were collected are included in Table 6. Only sites in Edgartown, Oak Bluffs, and Chilmark were closely monitored, where a total of 4 pairs successfully fledged 5 young (1.25 chicks/pair). No pairs were observed nesting west of Tisbury Great Pond this year, however they may have attempted nesting and lost eggs to predation or other causes early in incubation.

REFERENCES

Blodget, B.G. and S.M. Melvin. May 1996. Massachusetts Tern and Piping Plover Handbook: a manual for stewards. Massachusetts Division of Fisheries and Wildlife, Natural Heritage and Endangered Species Program, Westborough, MA.

Hecht, Anne. December 2000. Preliminary 2000 Atlantic Coast Piping Plover and Productivity Estimates. U.S. Department of the Interior, Fish and Wildlife Service, Sudbury, MA. December 2000 letter and enclosures. 10 pp.

Swanson, Debra L. 1999. Status of Rare Beach Nesting Birds on Martha's Vineyard. 1999 Field Report. Sheriff's Meadow Foundation, Vineyard Haven, MA.

Swanson, Debra L. 1998. Status of Rare Beach Nesting Birds on Martha's Vineyard. 1998 Field Report. Sheriff's Meadow Foundation, Vineyard Haven, MA.

Swanson, Debra L. 1997. Status of Rare Beach Nesting Birds on Martha's Vineyard. 1997 Field Report. Sheriff's Meadow Foundation, Vineyard Haven, MA.