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Effects of Disturbance on Staging Roseate Terns (Sterna dougallii)
on the Cape Cod National Seashore
Submission to the Edna Baily Sussman Foundation
Melissa Althouse
State University of New York
College of Environmental Science and Forestry
Background
The Roseate Tern (ROST) is a seabird of unique concern, in that up to ninety percent of
the northwest Atlantic population stages in a concentrated area in Cape Cod, Massachusetts
(MA) before annual migration to South America (US Fish and Wildlife Service [USFWS] 2010).
During 2008 and 2009, the majority of post-breeding ROST observed at Cape Cod National
Seashore (CCNS) used only 2.4 km² of intertidal areas and beaches during the post-breeding
staging period of July– September (Mass Audubon 2008, Jedrey et al. 2010). This concentration
renders the ROST vulnerable to local catastrophe and to chronic stressors at the sensitive premigration life stage when birds must accumulate energy for migration (Erwin 1980, Trull et al.
1999). Sites currently used by ROST during the fall staging period in MA are subject to various
forms of anthropogenic and natural disturbance (Trull et al. 1999, Mass Audubon 2008), which
may upset activity budgets of pre-migratory ROST (Jedrey et al. 2010). CCNS receives over four
million visitors annually, with peak recreational activity coinciding with the staging period and
tern/shorebird migration. The precarious status of many wildlife species that depend on CCNS
habitats, coupled with intense recreational use, creates a formidable management challenge.
Survival rates for the species are unusually low for a seabird (Spendelow and Nichols
1989, Spendelow et al. 1995, Nisbet and Spendelow 1999). Despite ongoing management efforts
at breeding colony sites (including monitoring, protection by wardens, fencing off nesting areas,
deployment of best boxes or other artificial nest-sites, gull and other predator-control operations,
and colony-site restoration) (Nisbet and Spendelow 1999, USFWS 2010), this population has
declined more than 20% since 2000 and now is estimated to be only about 3,100 pairs (USFWS
2010). Given the endangered status of ROST and its recent unexplained decline, this study will
provide critically important and timely information for the park’s shorebird management
program, and ultimately may help promote conservation of other migratory bird populations. In
addition, by focusing on disturbance to staging flocks of ROST and Common Terns (S. hirundo)
(COTE), managers supplied with the resulting information from this study will be able to
minimize and mitigate disturbance to dozens of species of shorebirds, including several species
listed by the U.S. Fish and Wildlife Service (USFWS) as Birds of Conservation Concern.
A majority of adult mortality occurs away from breeding colonies (Spendelow et al.
1995, Nisbet and Spendelow 1999). Causes of mortality have proven difficult to study, as flocks
disperse shortly after young fledge (Shealer and Kress 1994). In conjunction with an ongoing
Cooperative Roseate Tern Metapopulation Project (CRTMP), this study endeavored to elucidate
what is occurring during the post-breeding dispersal period, after the HY have fledged and
moved away from the breeding colonies, but before the birds depart the US on their migration to
South America. Our objectives were to, (1) quantify apparent survival of ROST during the post-
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breeding period in southeast Massachusetts, by analyses of resightings, and (2) create a GIS
datalayer and map detailing ROST distributions.
Methodology
Study Area
Cape Cod is a large peninsula extending 96.5 km into the Atlantic Ocean from the coast
of Massachusetts. Located on the outer portion of the Cape, CCNS is a national park that
encompasses over 18,000 ha of marine, estuarine, fresh water, and terrestrial ecosystems. Marine
and estuarine systems include beaches, sand spits, tidal flats, salt marshes, and soft-bottom
benthos. Freshwater ecosystems include kettle ponds, vernal pools, sphagnum bogs, and swamps.
Terrestrial systems include pitch pine and scrub oak forests, heathlands, dunes, and sandplain
grasslands (National Park Service 2014). Of this expansive park, more than 60% of the NW
Atlantic ROST population has been known to stage in only 2.4 km2 (Mass Audubon 2008,
Jedrey et al. 2010), often characterized by tidal flats, sandbars, or barrier beach islands. Within
these sites, recreational activities such as walking, hiking, dog-walking, bicycling, swimming,
water sports, beach sports, beach driving, fishing, and kayaking are all common (J. A.
Spendelow, USGS, personal communication).
Study sites along Cape Cod were selected based on published information and
preliminary field observations by project partner organizations indicating significant use by
ROST, and include: Hatches Harbor and Wood End, Provincetown; North Beach, South Beach,
and South Monomoy Island, Chatham; Nauset Marsh Complex, Eastham/Orleans; Race Point
North and South, Provincetown; High Head, Truro; Crowe’s Pasture, Dennis; Long Beach,
Plymouth; Eel Point, and Esther Island, Nantucket (Mass Audubon 2008, Jedrey et al. 2010, C.
Luttazi, Mass Audubon, personal communication).
Field Methods
Resighting and identification of individually colorbanded terns on CCNS and other
staging sites were made by collaborative research groups (SUNY ESF, Virginia Tech, Mass
Audubon, and the US Geological Survey) in standardized surveys throughout CCNS. These
surveys took place across known staging sites within CCNS that covered the range of types and
intensities of disturbance. Disturbance types, frequencies, and distances to flocks were observed
for ten minutes using binoculars and a spotting scope, from at least 100 m away from the center
of the flock. A GIS datapoint was collected for each observed flock using a GPS unit. Distance
and bearing to the flock was recorded using a laser rangefinder and lenstatic compass.
After the ten-minute disturbance survey was completed, we slowly walked, waded, or
kayaked toward the flock and remain close enough (usually within 40 m of the birds) for
identification. Data on flock size, species composition, and age structure based on total terns (if
less than 200) or scan-samples (for larger flocks < 200) were recorded at the beginning of each
session and again if major changes occur. Because staging flocks usually are in a state of flux,
observers continuously made identifications until the flock departed, no new colormarked
individuals were located, or the session had reached a total duration of two hours. Colorband
combinations and unique colorband codes were recorded on a handheld voice recording device.
These resighting surveys took place at one to two sites per day (depending on accessibility of the
site) from 16 July through 28 September 2014.
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Data Analysis
The first objective, to quantify apparent survival of ROST during the post-breeding
period in southeast Massachusetts by analyses of resightings could not be completed during the
time period of this internship. All resighting data was entered into a central database being
designed and managed by Mass Audubon. This database is still under construction, and as such
access to database records is severely limited. These analyses will be performed by MassAdubon
staff once the data are available.
The extent and timing of post-breeding staging site use by ROST within CCNS will be
quantified through a collaborative endeavor, by resighting surveys of individual hatch year and
adults from throughout the entire breeding range. Formal multisite mark-recapture/resighting
modeling approaches will be adapted for use in estimating staging site movement rates, fidelity,
and stopover duration at the staging sites. A combination of weekly intensive resight efforts,
daily data collected by the resighting crew, resightings from cooperators, and opportunistic
resighters will be used to fit a multistate model in program MARK, to determine the effect of
site-level disturbance categories on movement rates among sites and weekly apparent survival of
ROST. The best models will be chosen using information-theoretic, and movement and
residency rates will be based on either the clearly best model, or model-averaging.
Observations from resighting efforts will also be used to fit a multistate capture-recapture
model in order to determine residency rates and site use of staging terns as a function of sitelevel disturbance intensity (low, medium, high). Sites characterization of intensities of
disturbance was data-driven, and determined a posteriori.
Spatial analyses of ROST distribution were performed from 28 September to 25 October
2014. Points were loaded from GPS units into ESRI’s ArcMap. A map was created using other
publicly available data, from sources such as Mass.gov and the USGS National Map service.
Results
Apparent Survival
Analyses on apparent survival could not be completed during the timeframe of this
internship, as collaborators did not have the data processed in time for me to analyze it for this
report. Nevertheless, working as an intern for Mass Audubon not only gave me the opportunity
to work with one of the foremost researchers on endangered shorebirds and seabirds, but also
allowed me to gain skills in collecting demographic data and to put my Masters’ research on
disturbance at these staging grounds into a population context, and sharpened my field seabird
and shorebird identification skills. Additionally, working with Mass Audubon as a resighter
facilitated the identification of study sites for my M.S. data collection, and provided me with
connections with other local wildlife managers and stakeholders.
Flock Distribution
Mixed-species tern flocks were observed at a total of twelve eleven sites. Six of these
were from our main eight study sites (Hatches Harbor (PHH), Race Point North (RPN), and
Wood End (PWE), Provincetown; North Beach (CNB), and South Beach (CSB), Chatham;
Nauset Marsh (ENM), and Coast Guard Beach (ECG), Eastham/Orleans). Flocks were also seen
at Head of the Meadow (THM), Truro; Jeremy Point (WJP) and Marconi Beach (WMB),
Wellfleet; and North Beach Island (CNBI), Chatham (Fig. 1).
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Fig. 1: Roseate Tern staging site distribution within Cape Cod National Seashore, Massachusetts,
2014
Future Work
Remaining goals for this research include a more intensive investigation on the
movement of ROST within the CCNS. Additionally, more detailed look at the effects of
disturbance on behavioral and demographic rates of this population will be completed as part of
my Master’s research. This will involve using behavioral observations to categorize and quantify
both naturally occurring and human-related disturbances, including research-induced
disturbances resulting from legband resighting surveys, on the behavior of mixed-species flocks
of staging terns at sites that contain a large proportion of ROST.
Acknowledgements
This research would not have been possible without the financial support of the Edna
Baily Sussman Fountain, the Roy W. Glahn Memorial Scholarship Fund (CNY Wildfowlers
Association), and the National Park Service. I would also like to thank my major professor Dr. J.
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Cohen, Dr. J. Spendelow (USGS), Dr. S. Karpanty and K. Davis (Virginia Tech), Dr. K. Parsons
and C. Luttazi (Mass Audubon), and K. Iaquinto (USFWS) for their expertise and guidance.
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