2010 SOUTHEASTERN NATURALIST 9(2):385–394
Increased Abundance and First Breeding Record of the
Neotropic Cormorant (Phalacrocorax brasilianus) on the
Alluvial Plain of Mississippi
Katie C. Hanson1,*, Travis L. DeVault2, and Stephen J. Dinsmore3
Abstract - Phalacrocorax brasilianus (Neotropic Cormorant) has been observed
with increasing frequency in the alluvial plain (Delta region) of Mississippi. In
the past 6 years, 22 individuals have been observed in 20 separate sightings during
spring and summer. These sightings have occurred at breeding colonies of other
colonial waterbirds and commercial aquaculture facilities of Ictalurus punctatus
(Channel Catfish). Two sexually mature Neotropic Cormorants have been collected
at a colonial waterbird breeding colony near the Mississippi River in the western
Delta region among flocks of Phalacrocorax auritus (Double-crested Cormorants).
Twice during the summer of 2008, confirmed nesting of Neotropic Cormorants were
documented in the Delta region of Mississippi. The increased abundance and range
expansion of Neotropic Cormorants in the Delta region of Mississippi may be a result
of the readily available food source of cultured Channel Catfish.
The breeding range of Phalacrocorax brasilianus Gmelin (Neotropic
Cormorant) extends from South and Central America northward into the
southern United States, including southern Arizona, southern New Mexico,
north-central Texas, southwestern Louisiana, southwestern Arkansas, and
southeastern Oklahoma (Telfair and Morrison 2005). In the 1960s, Neotropic
Cormorant populations declined drastically in Texas (Telfair and
Morrison 2005), related perhaps to pesticide use (King 1989) and coastal
development (Oberholser 1974). However, since the 1970s, the number and
sizes of breeding colonies of Neotropic Cormorants have increased steadily,
and new breeding colonies have been established both along the coast of
the Gulf of Mexico and inland from southern Arizona to northwestern Louisiana,
southwestern Arkansas, and southeastern Oklahoma (Coldren 1998,
Green et al. 2006, Radamaker and Corman 2008, Telfair 2006). In Texas, the
coastal and inland breeding populations increased from 1968 to 1992. However,
while the coastal population declined from 1992 to 2004, the inland
population continued to increase (Telfair and Morrison 2005).
The range of Neotropic Cormorants also appears to be expanding. In
2007, there were new breeding records in central Kansas (Grzybowski and
1US Department of Agriculture, National Wildlife Research Center, Mississippi Field
Station, PO Box 6099, Mississippi State, MS 39762. 2US Department of Agriculture,
National Wildlife Research Center, Ohio Field Station, 6100 Columbus Avenue,
Sandusky, OH 44870. 3Department of Natural Resource Ecology and Management,
339 Science II, Iowa State University, Ames, IA 50011. *Corresponding author -
386 Southeastern Naturalist Vol. 9, No. 2
Slicock 2008a; S. Seltman and R. Graham, Kansas Ornithological Society,
Larned, KS, pers. comm.) and north-central Oklahoma (Grzybowski and
Slicock 2008b). In addition to an overall increase in the number of wintering
Neotropic Cormorants in Texas, a greater proportion of the wintering
population is now found inland. National Audubon Society Christmas Bird
Counts reveal that between 1957–58 to 1969–70, 99% of the population
was coastal; however, between 1970–71 to 2005–06, only 83% was coastal
A closely related and more thoroughly studied species, Phalacrocorax
auritus Lesson (Double-crested Cormorant), also has increased in
abundance, both in North America and in the southeastern US in recent
years (Hatch and Weseloh 1999, Jackson and Jackson 1995, Wires et al.
2001). Double-crested Cormorants wintering in the alluvial plain (Delta
region) of Mississippi increased by nearly 225% during the 1990s (Glahn
et al. 2000b), and have continued to increase since (Dorr 2006). Although
Double-crested Cormorants did not breed in the Delta region of Mississippi
historically, nesting of this species has occurred there over the past decade
(K. Hanson and B. Dorr, National Wildlife Research Center, Starkville,
MS, unpubl. data; Reinhold et al. 1998; Sauer et al. 2007). The increase
of Double-crested Cormorants in Mississippi has coincided with a dramatic
increase in commercial production of Ictalurus punctatus Rafinesque
(Channel Catfish) in Mississippi (Glahn and Stickley 1995, Glahn et al.
2000b, Mott and Brunson 1997). The Delta region of Mississippi comprises
more than 29,000 ha of water surface area used for commercial catfish production
Annual midwinter censuses of Double-crested Cormorants have been
conducted in the Delta region of Mississippi by USDA APHIS Mississippi
Wildlife Services (MS-WS) since the winter of 1989–90 (Glahn and
Stickley 1995), with no reports of Neotropic Cormorants to date. Surveys
of likely and confirmed Double-crested Cormorant breeding colonies have
been conducted by MS-WS in the Delta region since 1994, with the first
documented Double-crested Cormorant nesting occurring in 1998 (Reinhold
et al. 1998). Observations of Neotropic Cormorants have not been reported
in Mississippi during the National Audubon Society Christmas Bird Count
nor during the North American Breeding Bird Survey. Annual opportunistic
surveys for waterbirds have been conducted by S.J. Dinsmore (unpubl. data)
in spring and summer throughout the Delta region of Mississippi since 2001.
According to the Mississippi Ornithological Society, a Neotropic Cormorant
observed in the Delta region on 28 February 2003 represents the third published
sighting for the state and the first record away from the Mississippi
Gulf Coast (Knight and Knight 2003). The first and second records for the
state were seen at Bellefontaine Beach in Jackson County in 1979 and 1980,
respectively. An unconfirmed sighting was reported in 1990 at Waveland
Lagoon in Hancock County.
2010 K.C. Hanson, T.L. DeVault, and S.J. Dinsmore 387
We describe the increased abundance of the Neotropic Cormorant, the
presence of sexually mature adults, and first documented breeding attempt in
Mississippi based on recent observations. We also suggest that these recent
findings may be linked to the abundant food source provided by commercial
Channel Catfish aquaculture in the Delta region of the state.
From 2003 to 2008, we completed a mixture of opportunistic surveys and
targeted surveys of known and suspected colonial waterbird roosts, breeding
colonies, and catfish pond complexes during the spring and summer
months (late February through August) in the Delta region of Mississippi.
Opportunistic surveys (2003–2007; S.J. Dinsmore, unpubl. data) consisted
of systematic vehicular visits to catfish pond complexes and neighboring
natural water bodies to count waterbirds with an emphasis on shorebirds and
long-legged wading birds. Opportunistic surveys often visited >100 catfish
ponds in a day and were not surveys for nests. Targeted surveys (2005–2008;
K.C. Hanson, unpubl. data) were conducted on known colonial waterbird
roosts and breeding colonies and included nest counts of Double-crested
Cormorants, the presence of other species of nesting colonial waterbirds, and
their proximity to nesting Double-crested cormorants.
Upon observation, Neotropic Cormorants were assigned to 1 of 3 age
classes based on plumage characteristics described by Telfair and Morrison
(2005). Individuals were classified as adults if they displayed adult breeding
plumage, with glossy, nearly black feathers, a white-bordered gular pouch,
and white filoplumes present on sides of the head. Individuals were classified
as sub-adults if plumage was nearly black to fuscous in color, with a whitebordered
gular pouch but lacking any filoplumes on the sides of the head.
Individuals that lacked a white-bordered gular pouch and were fuscous in
color were classified as juveniles (young-of-the-year).
Two Neotropic Cormorant specimens were recovered during management
control operations of Double-crested Cormorants in the Delta region
of Mississippi during 2007 and 2008. Morphometric measurements were
collected and necropsies were performed on both specimens.
Surveys completed from 2003 to 2008 yielded repeated sightings of
adult, sub-adult, and juvenile Neotropic Cormorants at breeding colonies
of other waterbirds, night roosts of Double-crested Cormorants, and commercial
Channel Catfish aquaculture facilities (Table 1). The presence of
both breeding adults and juveniles in the Delta region during the spring and
summer months may be indicative of Neotropic Cormorants actively breeding
in the area. All sightings of Neotropic Cormorants were observed in the
presence of Double-crested Cormorants.
388 Southeastern Naturalist Vol. 9, No. 2
All but one observation of Neotropic Cormorants were in Humphreys,
Sunflower, and Washington counties, which are in the Delta region of Mississippi
(Fig. 1). These three counties comprise more than 50% of the total
water surface area (>20,000 ha) of Channel Catfish aquaculture in the state
of Mississippi (USDA 2008). Neotropic Cormorants that we observed at
aquaculture facilities often were loafing on pond levees with Double-crested
Cormorants, presumably because Channel Catfish aquaculture ponds provide
a readily available food source.
Neotropic Cormorants have been sighted multiple times at both Dutch
Brake and Cold Lake, which are adjacent to commercial Channel Catfish
aquaculture facilities and are Double-crested Cormorant roost sites. Neotropic
Cormorants also were observed in Washington County at Deer Lake and
Swan Lake at Yazoo National Wildlife Refuge, and at Swamp Roost. Both
Swan Lake and Swamp Roost serve as Double-crested Cormorant winter
roost sites and breeding colonies. Swamp Roost and Yazoo National Wildlife
Refuge are less than 9 km apart, with the closest aquaculture facility within
One adult male Neotropic Cormorant was shot unintentionally on 15
June 2007 by USDA APHIS Mississippi Wildlife Services personnel during
Double-crested Cormorant control operations at Swamp Roost, with birds
being salvaged as part of a Double-crested Cormorant reproductive status
Table 1. Recent observations of Neotropic Cormorants on the alluvial plain of Mississippi. A =
adult, S = subadult, and J = juvenile.
Date A S J County Location
28 Feb 2003 1 Humphreys Double-crested Cormorant roost at Cold Lake
01 Mar 2003 1A Humphreys Double-crested Cormorant roost at Cold Lake
03 May 2003 1 Humphreys Catfish aquaculture pond SE of Cold Lake
07 May 2003 1 Humphreys Catfish aquaculture pond SE of Cold Lake
09 Aug 2003 1 1 Adams St. Catherine Creek NWRC
30 Aug 2003 1 Humphreys Catfish aquaculture pond W of Isola, MS
21 Jul 2004 1 Washington Swan Lake, Yazoo NWR
07 Aug 2004 1 Sunflower Dutch Brake
13 Aug 2004 1 Washington Catfish aquaculture pond SE of Hollandale, MS
17 Jul 2005 1 Washington Deer Lake, Yazoo NWR
17 Jul 2005 1 Humphreys Catfish aquaculture pond E of Belzoni, MS
02 Jul 2006 1 Sunflower Dutch Brake
02 Jul 2006 1 Humphreys Catfish aquaculture pond S of Isola, MS
03 Aug 2006 1 Humphreys catfish aquaculture pond S of Isola, MS
03 Aug 2006 1 Sunflower Dutch Brake
15 Jun 2007 1 Washington Swamp Roost
15 Jul 2007 2 1 Sunflower Dutch Brake
07 May 2008 1B Yazoo Stuart Brake Ridge
03 Jun 2008 1B Yazoo Stuart Brake Ridge
09 Jun 2008 1 Washington Swamp Roost
ARepeat sighting of the bird observed the previous day.
BBird observed on nest.
CSt. Catherine Creek is located south of the Delta region of Mississippi.
2010 K.C. Hanson, T.L. DeVault, and S.J. Dinsmore 389
research project. Swamp Roost is an established mixed breeding colony of
Double-crested Cormorants, Anhinga anhinga L. (Anhingas), Ardea albus
L. (Great Egrets), Ardea herodias L. (Great Blue Herons), and Nycticorax
nycticorax L. (Black-crowned Night-Herons). The male Neotropic Cormorant
collected was in adult breeding plumage with white nuptial plumes on
the head and neck. Morphometric measurements taken included body mass
(1.12 kg), culmen length (52.8 mm), tarsus length (52.8 mm), and wing
chord length (258 mm). Upon necropsy, enlarged testes were observed (left
Figure 1. Locations within the Mississippi alluvial plain (Delta region) where Neotropic
Cormorants have been observed (2003–2008). Triangles represent colonial
waterbird breeding colonies. Circles represent Channel Catfish aquaculture pond.
390 Southeastern Naturalist Vol. 9, No. 2
testis length = 18.8 mm, width = 7.4 mm, mass = 0.403 g), indicating that
the bird was in active breeding status.
On 9 June 2008, an adult female Neotropic Cormorant was shot unintentionally
by USDA APHIS WS National Wildlife Research Center
personnel during Double-crested Cormorant control operations at Swamp
Roost, with birds being salvaged as part of a Double-crested Cormorant
food-habits research project. Morphometric measurements taken of the
adult female bird included body mass (1.13 kg), culmen length (49.2 mm),
tarsus length (53.3 mm), and wing chord length (252 mm). Upon necropsy
and examination of the reproductive tract, the presence of a striated and
convoluted oviduct and one pre-ovulatory follicle indicated the bird was
sexually mature and was in active breeding status. No post-ovulatory
follicles were observed, suggesting the bird had not laid eggs within the
previous few weeks. This finding was consistent with the later stage of
nesting (lack of post-ovulatory follicles in sexually mature females, and
presence of chicks and fledglings) observed in Double-crested Cormorants
within the breeding colony.
In the afternoon of 7 May 2008, an adult Neotropic Cormorant was
sighted in Stuart Ridge Brake perched in a Nyssa aquatica L. (Water
Tupelo) next to a nest. Shortly thereafter, the same bird was observed
and photographed climbing into the nest and remained there until dark.
Twenty-seven days later, on 3 June 2008, an adult Neotropic Cormorant
was sighted in the afternoon, at the same tree and nest. The bird remained
on the nest until dark. The presence of eggs or chicks in the nest was undetermined.
Stuart Ridge Brake is an established Double-crested Cormorant
breeding colony, located adjacent to a commercial Channel Catfish aquaculture
facility in Yazoo County. It also contains breeding Anhingas, Great
Egrets, Great Blue Herons, Black-crowned Night-Herons, and Eudocimus
albus L. (White Ibis).
The Mississippi Breeding Bird Atlas lists several criteria based on
the recommendations for North American Breeding Bird Atlas projects
(Laughlin et al. 1990) for confirmation of a breeding species. These criteria
include carrying nesting material, nest building, and observations of an
occupied nest. Based on these criteria, our observations qualify as a first
breeding record for the Neotropic Cormorant, and suggest that the species
may be expanding its range in inland Mississippi. Continued reports of
inland breeding colonies in eastern Texas, northwestern and central Louisiana,
southwestern Arkansas, southeastern and north-central Oklahoma,
and central Kansas further support the likelihood of additional breeding
colonies of Neotropic Cormorants becoming established in Mississippi
(Coldren 1998, Green et al. 2006, Grzybowski and Slicock 2008a, Radamaker
and Corman 2008, Telfair 2006, Telfair and Morrison 2005).
2010 K.C. Hanson, T.L. DeVault, and S.J. Dinsmore 391
Like Double-crested Cormorants, Neotropic Cormorants are opportunistic
foragers, typically foraging on fish that are most abundant (Telfair and
Morrison 2005). Telfair and Morrison (2005) note that the overall growth
pattern of the North American Neotropic Cormorant population is consistent
with expanding growth rates of other species of cormorants (van Eerden
and Gregersen 1995, Hatch and Weseloh 1999, Jackson and Jackson 1995).
Neotropic Cormorant populations have increased in the Greater Antilles and
Cuba in recent years, possibly as a result of fish-farming (Lee and Mackin
2009, Norton 1990, Telfair and Morrison 2005). Radamaker and Corman
(2008) also have noted that range expansion and increases in Arizona populations
of Neotropic Cormorants are likely due to an increase in availability
of prey. Highly prolific species of exotic tropical fish (Tilapia spp.) have
been introduced into Arizona and are frequent prey items of both Neotropic
and Double-crested Cormorants.
We observed Neotropic Cormorants at or nearby Channel Catfish aquaculture
facilities, often among Double-crested Cormorants. Glahn et al.
(2000a) documented improved overwinter body condition of Double-crested
Cormorants in the Delta region of Mississippi due to exploitation of commercially
raised Channel Catfish and hypothesized that the consumption of
Channel Catfish has increased Double-crested Cormorant survival and contributed
to a rapid increase in their population. Double-crested Cormorants
forage extensively at aquaculture facilities (Glahn et al. 1995), and Neotropic
Cormorants probably utilize this food source as well. The increased
abundance of Neotropic Cormorants in the Delta region may be due, in part,
to the overall regional expansion of their range. However, the readily available
cultured Channel Catfish in particular may facilitate their expansion
into the Delta region.
From May through September, Double-crested Cormorant control
operations can be conducted under the authority of a Public Resource Depredation
Order (PRDO), which allows state fish and wildlife agencies, tribes,
and USDA Wildlife Services to lethally take Double-crested Cormorants to
protect natural resources (USFWS 2003). Mississippi is one of the 24 states
covered by the PRDO. The presence and unintentional collection of Neotropic
Cormorants during control activities was unexpected. Until recently,
the presence of Neotropic Cormorants was unknown in any of the managed
Double-crested Cormorant breeding colonies. No other incidental take of
Neotropic Cormorants have been reported while operating under the PRDO
(Terry Doyle, US Fish and Wildlife Service, Arlington, VA, pers. comm.).
In addition to the PRDO, Double-crested cormorant control activities
may be conducted under the authority of an Aquaculture Depredation Order
(AQDO). This depredation order authorizes the take of Double-crested Cormorants
from aquaculture facilities in 13 states when they are committing
or about to commit depredations to aquaculture stocks. It also authorizes
USDA APHIS Wildlife Services to perform control activities at roost sites
392 Southeastern Naturalist Vol. 9, No. 2
in the vicinity of aquaculture facilities during the months of October through
the following April. Persons operating under either depredation order are
required to report the take of any migratory bird species other than Doublecrested
Cormorants to their Regional Migratory Bird Permit Office. To date,
no Neotropic Cormorants have been reported as incidental take under the
AQDO (Terry Doyle, US Fish and Wildlife Service, Arlington, VA, pers.
comm.). However, if numbers continue to increase in the region, potential
for incidental take under this order may also increase.
In conclusion, observations of Neotropic Cormorants at sites used by
Double-crested Cormorants (e.g., breeding colonies and catfish farms) in the
Delta region have increased. Information provided herein on the expansion
of Neotropic Cormorants in the Delta region should minimize inadvertent
take of Neotropic Cormorants during management control of the Doublecrested
Cormorant under both these orders.
We thank Valerie Burton and Wildlife Services, MS for their valuable assistance
in collection of Double-crested Cormorants in the Delta region of Mississippi.
Thanks to Scott Seltman and Rob Graham for their detailed accounts of recent
breeding Neotropic Cormorants in Kansas. We also thank Brian Dorr, Kris Godwin,
Shauna Hanisch, Patrick Smith, Mark Tobin, Linda Wires, and 2 anonymous reviewers
for providing valuable comments while reviewing the manuscript.
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