ResourcesGulf of Maine Library CollectionIdentification of Important Habitats in the Lower Casco Bay (Maine) WatershedChapter 12. Shorebird HabitatsGENERAL: Piping plovers (Charadrius melodus)
and least terns (Sterna albifrons) nest on dunes and beaches,
and forage on flats and in nearshore waters of Casco Bay. The plover is
listed as endangered by Maine and threatened by federal authorities; least
terns are listed as endangered by Maine. SOURCES OF BIOLOGICAL AND SPATIAL DATA: Data for the
least tern and piping plover coverages were obtained from Brad Allen and
Lindsay Tudor (MDIF&W), and Jody Jones of the Maine Audubon Society
(Audubon). MDIF&W shorebird foraging and roosting surveys date back
to 1979. Audubon has conducted nesting surveys of piping plovers since
1981, and least terns since 1977. The federal Recovery Plan (1987) for
the piping plover contains data summaries and extensive discussion of
management needs and actions; an updated revised plan is in draft. Plover and tern nest locations depicted in Jones and Camuso (1994) were
traced onto USGS 7.5' topographic quads, then digitized as point coverages.
CMGE digital quads for Small Point, Cape Elizabeth, and Prouts Neck provided
beach, intertidal and subtidal polygons which were interpreted as nesting
and foraging habitats (see below); NWI maps were used to identify some
intertidal foraging habitats. MDIF&W supplied coverages of plover
and tern Essential Habitats; these were used in establishing boundaries
for sensitivity zones. A digital representation of the Casco Bay coastline
was obtained from OGIS. HABITAT CONSIDERATIONS Least tern nesting: Although tern nesting beaches are relatively
dynamic, site fidelity is indicated by consistency of nesting efforts.
Atwood and Massey (1988) show that least terns in California are prone
to return to previous year colony sites, or move only short distances.
This implies conservation benefits from identifying and protecting long
term nesting areas and associated requisites, such as foraging habitats.
Least tern foraging: Least tern foraging habitats around nesting
areas were identified from figures in Jones and Camuso (1994). The areas
identified were well within the distances stated by Atwood and Minsky
(1983). The latter described foraging distances for breeding colonies
of least terns in California as "90-95% within 1 mile of shore in water
less than 60 feet in depth." Typical foraging habitat is within 2 miles
of colony sites in "relatively shallow nearshore ocean waters in the vicinity
of major river mouths...". Jones and Camuso observed the relative distributions
of terns feeding in the marsh behind the nesting area and the ocean in
front of it. They noted 93 of 468 feeding episodes in the marsh versus
375 over the ocean. Birds feeding in the marsh tended to stay relatively
near the nest area, but range more widely when feeding over the ocean.
Piping plover nesting: Piping plovers nest on dynamic coastal
beaches and sand spits above the high tide line. Nesting substrate consists
of sand and gravel or shells, in which the birds excavate a shallow depression.
Nests are typically situated in open sand, but can also be found in sparse
or moderately dense beach grass. Nesting occurs from April through late
July. Chicks are mobile shortly after hatching and fledge by the end of
August. Piping plover foraging: Piping plover adults and chicks feed on
invertebrates on intertidal beaches and flats, and on organisms associated
with beach wrack. During the reproductive season, feeding areas generally
are contiguous with nesting and brood rearing areas. Jones and Camuso
observed 65 of 453 feeding events over the marsh behind nesting beaches
versus 388 on the ocean side. MANAGEMENT CONCERNS Most Maine piping plover nests are now individually protected by fencing
to exclude predators and pedestrian or vehicular traffic (Jones 1993);
these efforts enhance nesting success even within relatively developed
locations. Such intensive persistent management to some degree substitutes
for imposition of large passive natural protective buffer zones, which
are infeasible due to the high level of recreational use and development
of southern Maine beach sites. Least terns nest colonially, so protection
of their nests from predators has been far less effective than for plovers
(Jones 1993). For this reason more remote (island) beaches should be examined
for possible establishment or natural maintenance of tern and plover populations.
This was the purpose for our identification of potential nesting habitat
(see below). We attempted to map sensitivity zones in which development may degrade
the adjacent habitats. This was set at 90 m (295') for nesting, potential
nesting, and feeding habitats, based on information collected by Robert
Buchsbaum (ms.) His distances for shorebird tolerances, 180' to 300',
agree with MDIF&W buffer zones for riparian habitats (Jones et. al.
1988). Finally, we overlaid our coverage onto the MDIF&W designated piping
plover and least tern Essential Habitats. Any Essential Habitat areas
not already within our coverage were then included as an additional sensitivity
zone. MAPPING OF HABITATS Observed nesting areas: Least tern and piping plover nesting areas
for the lower 15 towns in the lower Casco Bay watershed were identified
from Maine Audubon's 1994 Piping Plover and Least Tern Project Report
(Jones and Camuso 1994). Nesting areas were overlaid on CMGE digital quads,
and the corresponding CMGE beach polygons were selected for our shorebird
coverage. Known nesting areas were scored 8. Potential nesting areas: The CMGE maps displayed many beach areas
on the mainland and islands which might offer additional or alternative
nesting habitat for terns and plovers. Polygons with suitable designations
were selected (Table 4), the characteristics examined further on USGS
quads and black and white aerial photos, then placed into the coverage
if deemed to be similar to areas used by these birds. Next we eliminated
potential nesting areas smaller than smallest beach area in use (11,000
sq m, about 2.7 acres), based on comments by John Atwood (Manomet Observatory,
pers. com.). Potential nesting areas were scored 4. Table 4. Polygon Types Included as Suitable Nesting or Foraging
Habitats for Least Terns and Piping Plovers. Tern Foraging: Coastal Marine Geologic Environment Categories B1: intertidal sand beach C2: medium velocity tidal channel C7: Inlet channel F1: Coarse grained flat Me: ebb tidal delta Mf: flood tidal delta Mp: point or lateral bar National Wetland Inventory Categories E2US3N: estuarine intertidal, unconsolidated mud shore M2US3N: marine intertidal, unconsolidated mud shore Plover Foraging: Coastal Marine Geologic Environment Categories M1: High salt marsh B1: sand beach Mp: point or lateral bar National Wetland Inventory Categories E2US3N: estuarine intertidal, unconsolidated mud shore M2US3N: marine intertidal, unconsolidated mud shore E2EM1P: estuarine intertidal, emergent vegetated Tern and Plover Nesting: Coastal Marine Geologic Environment Categories Sd: dunes, vegetated beach ridge Feeding areas: Foraging habitats were added to our coverage by
selecting CMGE polygons having the appropriate tidal and substrate characteristics
(Table 7) and located within the areas most frequently used, based on
depictions in Jones and Camuso. Additional foraging areas were selected
from the CMGE and from National Wetland Inventory (NWI) digital maps,
based on correspondence with the MDIF&W shorebird database. Known
feeding areas were scored 8 for habitat quality. Essential Habitats: areas which were outside the above habitats
and sensitivity zones, and within the piping plover and least tern Essential
Habitats were scored 4. Adjustment for impacts from existing development: The above habitat values
were reduced by half if within a 90 m wide "impact" zone around existing
development. Areas which are currently developed were scored 0. The coverages are intended as representations of environmentally suitable land and water areas for the two species but are not intended to depict areas being managed or under regulatory control, such as Maine Essential Habitats, or federal Critical Habitats. The combined habitats for terns and plovers is shown in Figure
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