Energy and Power Engineering, 2010, 2, 143-147
doi:10.4236/epe.2010.23021 Published Online August 2010 (http://www.SciRP.org/journal/epe)
Migratory Behavior of Franklin’s Gulls
(Larus pipixcan) in Peru
Joanna Burger1, Michael Gochfeld2, Robert Ridgely3
1Division of Life Sciences, Rutgers University, Piscataway, USA
2Environmental and Occupational Medicine, UMDNJ-Robert Wood Johnson Medical School, Piscataway, USA
3N. Sandwich, New Hampshire, UK
Received March 29, 2010; revised May 10, 2010; accepted June 20, 2010
Abstract
Information on the migratory pathways for birds is essential to the future citing of wind power facilities, par-
ticularly in off-shore waters. Yet, relatively little is known about the coastal or offshore migratory behavior
of most birds, including Franklin’s gulls (Larus pipixcan), a long-distant migrant. We report observations
along the coast of Peru made in November 2008 to determine where birds concentrated. Wind facilities can
not avoid regions of high avian activity without knowing where that activity occurs. Migrant flocks of 250 to
50,000 were observed on coastal farmfields, dumps and estuaries, on beaches and mudflats, and up to 45 km
offshore. Bathing and foraging flocks ranged in size from 20 to 500 birds, and most flocks were monospeci-
fic, with occasional grey-headed (Larus cirrocephalus) and band-tailed (L. belcheri) on the periphery. While
previous notes report Franklin’s gulls foraging coastally, we found flocks feeding up to 45 km offshore by
diving for prey or feeding on the water. The relative percentage of birds of the year varied in migrant flocks
from zero to 14%, with lower numbers of young foraging aerially on insects (only 1%). The percentage of
young feeding over the ocean decreased with increasing distance from shore; no young of the year were re-
corded at 36-44 km offshore. While there were large flocks of Franklin’s gulls resting on the water inshore,
the number of gulls foraging offshore did not decline up to 45 km offshore. The presence of foraging flocks
of Franklin’s gulls out to 45 km offshore, and occupying space from 0 to 20 m above the water, suggests that
they would be vulnerable to offshore anthropogenic activities, such as offshore drilling and wind facilities.
Keywords: Migration, Larus pipixcan, Franklin’s Gulls, Gulls, Migrants, Young of the Year, Habitat Use,
Flock Associations, Wind Farms, Offshore Drilling
1. Introduction
The siting of wind facilities has become an important
topic as governments and industry consider the possibil-
ity of large-scale offshore facilities. Yet little is known of
the ecology and behavior of species, such as marine
mammals, fish, and birds, in offshore regions where
wind facilities might be sited. Before siting many such
facilities, it is essential to understand whether the loca-
tions would impact ecological resources in these sites.
The migratory behavior of birds is an important, but
often little studied aspect of their life cycle, mainly be-
cause long-distance migrants are difficult to study. They
often migrate at night, at high altitudes, or at unpredict-
able places and times. Further, scientists often focus on
the breeding season, or on native species, or on the rare
migrants, making information on abundant migrants par-
ticularly lacking. Yet, for many species, migration is one
of the most risky life stages, because of predation,
weather conditions, obstacles (such as buildings or tow-
ers [1,2]), or lack of foraging habitats [3-8].
Information on the locations, habitats, and timing of
migration is needed to understand both the vulnerability
of a species to natural forces, as well as to potential an-
thropogenic activities, such as wind facilities. While sci-
entists have long recognized the threats to migrants of
anthropogenic terrestrial threats, such as buildings and
towers [1,9,10], little attention has been devoted to
coastal and offshore migrants. With the recent focus on
renewable energy, many countries are turning to offshore
wind farms, and the question of risk to avian populations
that migrate offshore is coming to the fore, with the re-

J. BURGER ET AL.
144
alization that there is a lack of information on the spe-
cific locations of common and abundant migrants along
coasts, and out to the edge of the continental shelf.
In this paper we report on observations of migrant
Franklin’s (Larus pipixcan) Gulls in coastal Peru. We
were particularly interested in flock locations (distribu-
tion along the coast), habitats, and in the percentage of
young of the year present in flocks (an indication of re-
productive success). Little quantitative information is
available on migrant Franklin’s Gulls in South America
[11]. They were believed to migrate mainly offshore over
the ocean, and in Peru to migrate low over the deserts
[12], but timing, flock size, habitat use, and flock asso-
ciations were poorly known [11].
2. Methods
All observations were made in Peru from 1 to 23 No-
vember 2008. We visited freshwater marshes, coastal
marshes, and beaches from south of Lima to northern
Peru, recording the numbers of adult and young of the
year Franklin’s Gulls, along with other species of gulls
that were present. Counts of adults and young of the year
were made at each location. Photographs were also taken
of flocks both on the ground and in the air, and these
were enlarged digitally to confirm counts and the ratio of
adults to young of the year.
On 5 November 2008 we travelled 44 km offshore
from Lima.
3. Results
Migrant flocks of 250 to 50,000 Franklin’s Gulls were
observed on coastal farmfields, dumps and estuaries, on
beaches and mudflats, and up to 45 km offshore (Table
1). Most flocks were either migrating or coming in to
roost or preen, but some flocks were feeding aerially on
insects, and these contained very few young (1%). At
several locations (Villa, Ventanilla) we observed flocks
descending from high altitudes (out of range of binocu-
lars) to the beach or marsh locations to drink, bath, and
preen vigorously.
Bathing and foraging flocks ranged in size from 20 to
500 birds, but resting flocks ranged up to 50,000. A high
percentage of gulls in resting flocks were engaged in
vigorous preening (up to 60%). While previous notes re-
port Franklin’s gulls foraging coastally, we found flocks
feeding up to 45 km offshore by diving for prey or feed-
ing on the water (Table 2). Although there were large
flocks of Franklin’s Gulls resting on the water inshore,
the number of gulls foraging offshore did not decline up
to 45 km offshore.
Table 1. Observations of Franklin’s Gulls (Larus pipixcan) from Peru (November 2008). Young of the year accounted
for ??% of the gulls (where counts could be made visually and from photographs).
Date Location Habitat
Number of Franklin’s Gulls
(% young of the year) Presence of other species
1 November Bayovar, N. Peru Beach 50,000 + (not recorded)
2 November Villa, near Lima Freshwater pool 800 (10) Band-tailed gulls
Beach dunes 5000 (12) Grey-headed gulls at edge of flock
Nearby saltwater 5000 (12) None
In air, hawking insects 200 (1) None
5 November Lima harbor out to 44 km Coastal/ocean 14,260 (2) Mainly monospecific
6 November 80 km north of Lima Aerial migrants,
5 km from coast 300 (8) None
Ventanilla Freshwater marsh near coast273 (10) None
Ventanilla Aerial migrants above town2,100 (not recorded) None
8 November Pimentel Pimentel beach,
sewage outfall, and mudflat310 (11)
Dense monospecific with flocks of
20 grey-headed and 30 kelp gulls on
edge, and 3 elegant terns within
Franklin’s Gull flock
Santa Rosa Santa Rosa Beach 1325 (11)
Dense monospecific flocks with
grey-headed and band-tailed at
edges; a short distance away was
a dense flock of 2,500
grey-headed gulls
Garbage dump 254 (18) None
Wet marshes and farmfields1513 (15) None
9 November Abra de Porcuya
(east side) Flying over Andes 1 (adult) None
23 November Villa, Lima Beach, marshes and ocean 10,000 (14+)
Kelp, Band-tailed and Grey-headed
in nearby flocks, with some at
edges of Franklin’s Gull flocks
Note: Percent of young based on visual and photographic counts except 1 and 23 November, and for the aerial flock at Ventanilla (where the light
prevented aging of the gulls).

J. BURGER ET AL.
145
Table 2. Number of Franklin’s Gulls in a coastal transect out to 44 km (Lima, Peru, November 5, 2008). Such information is
directly relevant to offshore activities, such as shipping, oil drilling and wind farm construction.
Distance from shore (km) Number of Franklin’s Gulls in air
(additional gulls rafting on water)
Percent of young of the year in flying or
feeding flocks
0-4 2316 (4,200) 8
4.1-8 803 (1000) 4
8.1-12 918 (110) 5
12.1-16 74 (210) 0
16.1-20 330 1
20.1-24 300 (156) 0
24.1-28 279 3
28.1-32 804 (408) 0
32.1-36 1028 (76) 2
36.1-40 577 (180) 0
40.1-44 491 0
The relative percentage of birds of the year varied in
migrant flocks from zero to 14%, with lower numbers of
young foraging aerially on insects (only 1%, Table 1).
The percentage of young feeding over the ocean de-
creased with increasing distance from shore; no young of
the year were recorded at 36-44 km offshore. The gulls
we observed were mainly occupying the vertical space
from the water to 20 m above the water (although mi-
grants were much higher), but were concentrated below
10 m.
Most flocks were monospecific, with occasional Grey-
headed (Larus cirrocephalus) and Band-tailed (L.
belcheri) Gulls on the periphery (Table 1). At some
beaches, there were discrete and dense flocks of these
two species, along with discrete flocks of kelp gulls (La-
rus dominicanus) a few meters or hundreds of meters
from the Franklin’s Gulls. Franklin’s Gulls resting or
roosting on beaches often stood in very dense flocks,
nearly touching one another.
Even in dense migrant flocks, Franklin’s Gulls are
vulnerable to predators. On 23 November, two Franklin’s
Gulls were killed by two different Peregrine Falcons
(Falco peregrinus) visible at the same time. In one case
an immature Peregrine flew up to a Franklin’s Gull flock
swirling over land and flipped upside down to snatch a
gull’s breast, riding with it to the ground. Five minutes
later, a second immature Peregrine rose higher than a
different gull flock, and dove into it in the classic manner.
Although the gull flock scattered, the Peregrine pursued
one bird until it slammed into the gull, exploding the gull
and forcing it to the ground.
Two additional observations bear mention: 1) In late
October 2007, several flocks of 600-1000 birds flew high
overhead (at the limit of binocular vision) at the La Ven-
tosa area of the Isthmus of Tehuantepec in Mexico; other
flocks (100-1000) flew low and close to shore moving
south and east (A. Farnsworth, pers. comm.). In 2003,
Franklin’s gulls had only just begun to reach the northern
beaches of Chile (Valparaiso to Astero Lampa Santiago
de Pacifica): from 9-10 November fewer than 20 gulls
were observed at each of several different beaches, but
by 10-12 November the number had built up to 100 at
several locations (F. Lesser, pers. comm.).
4. Discussion
With the world-wide development of renewable energy
resources, such as wind power, it is essential to deter-
mine before facilities are built whether there are conflicts
with wildlife that would provide an ecological threat that
would impact operations. Many of the initial sitings of
wind facilities were within migratory or overwintering
ranges of birds, and resulted in high avian mortality, and
some curtailing of operations [13,14]. This paper pro-
vides data that can be used in considering the offshore
patterns of migratory gulls, particularly Franklin’s Gulls.
The Franklin’s Gulls observed in this report were
likely migrants just arriving in Peru, as judged by the
large dense flocks engaged in vigorous preening, and
their descent in large and continuous flocks from high
altitudes. That is, when we scanned the sky with binocu-
lars in areas where birds were descending, we could just
make out birds at the limit of binocular vision still de-
scending. The presence of relatively large flocks of 5,000
to 50,000 birds suggests that they were arriving, and had
not spread out along the coast.
Like other authors [12,15,16] we found them mainly
along the coast, but one was in the Andes. Birds found in
the high Andes may well be either lost, or merely on a
different migration route.
While many different foraging and migratory habitats
have been reported for Franklin’s Gulls in North Amer-
ica, few have been recorded for South America [11].
Habitats recorded in South America include fishmeal
plants, rivers, coasts, and behind trawlers [17,18]. We
found them resting, bathing and foraging on beaches,
saltwater and freshwater marshes, sewage outfalls, farm-
fields, and garbage dumps. While these habitats are not
unexpected, given their use of them in North America, it

J. BURGER ET AL.
146
requires documentation.
For most flocks, about 10-12% of the gulls were
young of the year, although far fewer young were in
flocks offshore and almost none engaged in aerial hawk-
ing for insects. This is not surprising, since both aerial
foraging and foraging offshore on fish are more difficult
foraging tasks than feeding on invertebrates along the
shore or on garbage [19-22]. That 10-12% of the flocks
are young of the year indicates successful reproduction
and migration over thousands of km; there are no previ-
ous data on percentages of young in migrant flocks in the
southern US, Central America or South America.
The presence of flocks of foraging and resting gulls
out to 45 km indicates that this species would be vulner-
able to any human activity on the continental shelf.
While it has previously been reported that Franklin’s
Gulls may migrate over the ocean, there were no quanti-
tative data on numbers or distances from shore. Further,
reporting that gulls migrate over the ocean does not in-
dicate the location of these birds (either longitudinally or
horizontally). In this study we report birds resting and
feeding on the water, and flying above the water at ele-
vations that would put them at risk from anthropogenic
activities on the water. That is, there were gulls in every
4 km block from 0 to 44 km offshore, and there were
gulls flying from the water level to 20 m above the water.
As governments and companies strive to diversify energy,
there is a need to have both qualitative and quantitative
information on the spatial envelope birds occupy at dif-
ferent times of the year. The data in this paper indicate
that migrating (and potentially overwintering) Franklin’s
Gulls in Peru occupy an envelope of space from 0 to 45
km offshore (and likely further out) and from 0 to 20 m
from the water’s surface. Migrants descending from the
sky came through space from the limit of binocular vi-
sion directly to the water or land.
5. Acknowledgements
We thank L. Navarette and A. Farnsworth for field com-
panionship and data, F. Lesser for data from Chile, G.
Engblom for insights on the species in pelagic waters,
and Lelis Navarette for logistical help and field observa-
tions while we were in Peru.
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