ResourcesIdentification of Important Habitats in Coastal New HampshireChapter 22. Great Blue HeronWading birds are conspicuous wildlife of coastal and inland wetlands,
and long have been regarded as biological indicators of environmental
quality. The great blue heron, Ardea herodias, occurs in the
study area and is on the GOMC species list. The following describes a
simple foraging habitat model for the great blue heron in relation to
known nesting habitats. The biological information was compiled
from the literature and data from the New Hampshire Audubon Society.
Nesting Habitats Locations of great blue heron breeding colonies were provided by Chris
Martin, New Hampshire Audubon Society. Five colonies have been occupied
in recent years within the study area and three more colonies adjacent
to it. We mapped nesting habitat as the entirety of the specific scrub/shrub
or forested wetland NWI polygons encompassing the nest sites. These were
selected from digital maps. All were scored as having a habitat suitability
of 10 (0 to 10 scale), based on the observed level of use. Foraging Habitats The relative value of foraging habitat is related to intrinsic characteristics
(abundance of prey, accessibility of prey) and, for these colonial nesting
birds, distance from roosts or colony sites (Erwin et al., 1993). Themes
used to characterize foraging habitat suitability included bathymetry,
NWI wetland types, and eelgrass distribution (Figure
of Feeding Habitat). Habitat suitability scores were assigned in two
phases: (1) scoring by cover type and depth, and (2) scoring based on
distance from known colony sites. 1. Score based on wetland type and depth: Habitat quality for
foraging herons was evaluated using data on relative use of wetland types.
In Maine, breeding great blue herons used inland freshwater wetlands associated
with greater wetland area, more extensive beds of emergent vegetation,
longer shorelines, and less open water than unused wetlands (Gibbs et
al. 1991). Wetland types used by herons in order of decreasing use (individuals/100
hours of observation) were palustrine emergent, palustrine aquatic bed,
palustrine scrub-shrub, lacustrine, palustrine forested, and palustrine
unconsolidated bottom (Gibbs et al. 1991). Use of wetlands for wading
bird foraging is likely to be associated with the abundance and the availability
of prey. Chapman and Howard (1984) regarded estuarine intertidal wetlands
as more valuable than marine wetlands for common egrets, which have feeding
habits similar to those of great blue herons. The former is likely to
have more concentrated and vulnerable prey. NWI wetland types were scored
as shown in Table 9 ('SUITABILITY SCORE 0-5'). Eelgrass beds were scored
as estuarine intertidal aquatic bed. Estuarine and marine wetlands where
water depth was deeper than 2 feet mlw were considered unavailable to
foraging herons and assigned a value of 0. 2. Score based on distance from colony sites: Wading bird colonies
apparently are located at sites remote from predators and disturbance,
yet within range of wetland foraging areas (Gibbs and Woodward 1984).
Wetlands within a 10 km radius of breeding colonies were considered higher
value foraging habitat than similar wetlands located beyond this distance.
Closer wetlands offer savings in travel time and energy expenditure for
adult birds and reduced exposure of young birds at the colony sites. Wetlands
within a 10 km radius of breeding colonies were scored double (Table 7;
'SCORE IF <10 km FROM COLONY') the habitat suitability of more distant
areas (Banner and Libby 1995). Table 7. Wetland Suitability as Great Blue Heron Foraging Habitat.
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