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First Records of Least Terns Nesting on Non-Gravel Roofs
T. Natasha Warraich1, Ricardo Zambrano1,*, and Elizabeth A. Wright2
Abstract - Sternula antillarum (Least Tern) and other waterbirds have nested on tar-and-gravel
roofs in Florida starting from the early 1950s. Habitat disturbance and loss has been implicated as
the primary reason for this shift from the ground to roofs. The Florida Fish and Wildlife Conservation
Commission conducted a statewide survey of rooftop-nesting birds between April and July
2010. Two buildings with non-gravel roofs were found to contain Least Tern nests; one was located
on Islamorada in the Florida Keys, and the other on Pensacola Beach in the Florida Panhandle.
Both of these sites were formerly gravel roofs and were used for nesting by Least Terns for several
years; however, they had both been recently reroofed. The Islamorada site has a spray polyurethane
foam roof, and the Pensacola Beach site has a mineral built-up roof. Both sites produced chicks,
but only the Pensacola site fledged young. These are the first published records of a waterbird
species nesting on a non-gravel roof. This discovery may have future implications as gravel roofs,
particularly in Florida, are being replaced by newer types of roofs that are safer to humans and
surrounding structures during tropical storms and are more energy efficient. Further surveys are
needed to determine the extent of Least Tern nesting on non-gravel roofs and the productivity of
these rooftop breeding colonies.
Sternula antillarum Lesson (Least Tern) traditionally nest on flat beaches, sandbars,
and spoil islands, which have coarse sand or shells with little to no vegetation
(Thompson et al. 1997). However, because of habitat loss due to coastal development,
an increase in human disturbance, and mammalian predation, Least Terns and other
beach nesting birds such as Rynchops niger L. (Black Skimmer), Gelochelidon nilotica
Gmelin (Gull-billed Tern), Sterna dougallii Montagu (Roseate Tern), and Haematopus
palliatus Temminck (American Oystercatcher) have been documented to nest on tarand-
gravel roofs (Douglass et al. 2001, Gore et al. 2008, Lott 2006; Thompson et al.
1997, Zambrano and Smith 2003, Zambrano et al. 2000). A tar-and-gravel roof (hereafter
a gravel roof) consists of a layer of tar spread over a roof and then covered with a
layer of gravel (DeVries and Forys 2004).
This rooftop nesting behavior was first reported for Least Terns in Miami Beach, FL
in the early 1950s (J.K. Howard in Fisk 1978) and has since been recorded in Maryland,
North and South Carolina, Georgia, Mississippi, Louisiana, and Texas (Butcher et al.
2007, Jackson and Jackson 1985, Krogh and Schweitzer 1999). In Florida, Least Terns
increasingly have used roofs for nesting, and rooftop nests now outnumber those in
ground-nesting colonies. Zambrano et al. (1997) found 93% of Least Terns breeding in
southeast Florida nested on roofs and Gore et al. (2007) found 74% of Least Tern colonies
on roofs statewide. The Least Tern is listed as a threatened species in Florida, in part,
because of the loss and degradation of habitat for ground-nesting colonies (Florida Fish
and Wildlife Conservation Commission 2010).
The Florida Fish and Wildlife Conservation Commission (FWC) conducted a comprehensive
statewide survey from April through June 2010 of historically used and newly
reported sites with roof-nesting seabirds and shorebirds. Surveyors visited each site at
least once to conduct a peak count of nests and adults where present, and to determine the
1Florida Fish and Wildlife Conservation Commission, 8535 Northlake Boulevard, West Palm
Beach, FL, 33412. 2239 8th Street, Apalachicola, FL 32320. *Corresponding author - Ricardo.Zambrano@
Notes of the Southeastern Naturalist, Issue 11/4, 2012
776 Southeastern Naturalist Vol. 11, No. 4
site’s current roof type. Follow-up visits were made to active breeding sites to conduct
counts of chicks and fledged young. Sites that initially were inactive but still had gravel
roofs were surveyed multiple times to determine whether colonies might have been established
later in the season. Surveyors typically did not revisit sites that no longer had
gravel roofs. To minimize disturbance, surveys were conducted from the periphery of the
colony or from a nearby roof using binoculars or spotting scopes, otherwise walk-through
nest counts were conducted.
Out of 474 sites surveyed in Florida during 2010 statewide, 22% (n = 103) had been
reroofed and converted from gravel to newer, non-gravel materials. Least Terns were
found nesting on 2 of those non-gravel roofs. These are the first published records of a
waterbird species nesting on a non-gravel roof. One site was located in Islamorada in
the Florida Keys, and the other site was in Pensacola Beach, in the Florida Panhandle.
Both sites were used historically by Least Terns as breeding sites (Gore et al. 2007), both
formerly had gravel roofs, and both had been re-roofed with a non-gravel material. Coincidentally,
nesting on these non-gravel roofs was first documented at both sites on 28
The Islamorada building had a spray polyurethane foam (SPF) roof that consisted of
two different components: a light grey elastomeric coating membrane over polyurethane
foam (National Roofing Contractors Association 2010b). This site was visited 4 times between
May and July 2010. A maximum of 10 nests and 3 chicks was observed at this site.
No fledged young were recorded before the site was found abandoned on 27 July 2010.
One of the tenants informed us that the roof was converted to an SPF roof in November
2009 and that the Least Terns had nested there for over 25 years (D. Bailey, Islamoradora,
FL, pers. comm.). As a follow-up, this site was resurveyed during the 2011 nesting
season. Two Least Tern nests were observed on 12 May 2011, and 3 Least Tern nests, 1
flightless chick, and 1 fledged young were recorded on 27 June 20 11.
The Pensacola Beach site had a mineral built-up roof, consisting of asphalt-based
roll roofing with a sprayed-on surface coating of fine white mineral granules in a polymer
base (L. Jackson, Pensacola Beach, FL, pers. comm.; National Roofing Contractors
Association 2010a). This site was visited 7 times between May and July 2010 on an approximately
weekly basis. A maximum of 2 Least Tern nests and 1 chick was observed.
One fledged young was observed flying from this roof and returning to it repeatedly on
12 July 2010. It is unclear how long Least Terns had been nesting on the Pensacola Beach
site: FWC records indicate it was identified as active in 1993 and 1998–2000 (Gore et al.
2007, Hovis and Gore 2000). Its gravel roof was replaced with the current roofing material
in late 2005, following hurricane damage (L. Jackson, pers. comm.). Due to logistical
and personnel constraints, this site was not resurveyed in 2011.
Prior to our study, roof-nesting Least Terns had only been recorded on gravel roofs.
This decline in the availability of gravel roofs for breeding sites was not unexpected
because many buildings owners in Florida are phasing out gravel roofs. Gravel roofs
generally have lower solar reflectance and lower heat emittance than new roof materials.
New buildings in Florida, must comply with the Florida energy code which sets minimum
standards for energy efficiency of roofs (DeVries and Forys 2004). Federal tax incentives
also encourage the replacement of gravel roofs with more energy efficient ones (US Environmental
Protection Agency 2010). Further, gravel on these roofs may be picked up
by strong winds during strong storm events and can cause projectile damage to adjacent
structures (US Department of Housing and Urban Development 1993). This has led to at
least one state’s building commission to propose legislation prohibiting the use of gravel
2012 Southeastern Naturalist Notes 777
on roofs (Florida Department of Community Affairs 2010). Given that the average life
span of a gravel roof is 20–25 years, DeVries and Forys (2004) estimated that most of
these roofs would no longer be available in 20 years. Both non-gravel-roof sites discussed
in this paper are historically used sites which formerly had gravel roofs. It is unknown
whether Least Terns or other beach-nesting birds will nest on non-gravel roofs that have
no prior history of use as breeding sites. More information is needed on the reproductive
success of beach-nesting birds utilizing non-gravel roofs. If future surveys find certain
types of non-gravel roofs more suitable for successful nesting and fledging of young than
others, it may be appropriate to recommend these roof materials to developers and building
owners or provide financial incentives to encourage their us e.
Acknowledgments. We thank Drs. Jeanette Wyneken, Terry Doonan, and Jim Rodgers
for reviewing earlier versions of this manuscript.
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