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2011 SOUTHEASTERN NATURALIST 10(4):659–672
Food Habits of American Alligators (Alligator
mississippiensis) in East Texas
David T. Saalfeld1,*, Warren C. Conway1, and Gary E. Calkins2
Abstract - American Alligator (Alligator mississippiensis) food habit data are important
when establishing management strategies, as diet can directly influence growth rates,
body condition, behavior, and reproduction. Diets of American Alligators are hypothesized
to vary among habitats as well as geographically; however, few diet studies have
been conducted outside of Florida and Louisiana. To address this information gap, 62 diet
samples were obtained from alligators ranging in size from 94.7 cm to 386.0 cm (total
length) from June 2006–September 2008 in inland freshwater wetlands in East Texas.
A total of 33 different prey items (comprising 670 individual prey items) and 1 parasite
were identified. Irrespective of size class, sex, and study site, >85% of individual prey
items were invertebrates. Nearly all diet samples contained some sort of organic by-catch
and/or non-food items (i.e., woody debris, aquatic plants, seeds, rocks, fishing tackle,
etc.). Although alligator diets were similar between sexes, non-breeding (<183.0 cm in
total length) alligators consumed more invertebrate prey items by biomass and percent
occurrence than breeding-size alligators. In general, alligators forage opportunistically;
therefore, most habitat-based, local, or geographic variability in food habits among populations
are most likely influenced by food availability. As such, regional differences in
food availability likely result in geographic variability in life-history characteristics such
as growth rates and condition, important factors to consider when establishing management
Throughout the southeastern United States, Alligator mississippiensis Daudin
(American Alligator) exist as top carnivores in aquatic and wetland systems,
and perform important functions in structuring coexisting animal populations
within their environment (Barr 1994, 1997; Mazzotti et al. 2009; Rosenblatt and
Heithaus 2011). Opportunistic predators, alligators exhibit a varied diet, and are
adept at exploiting local prey resources that encompass a wide diversity of sizes
and taxa, ranging from small insects and crustaceans to large vertebrates (Chabreck
1971, Delany and Abercrombie 1986, Rice 2004, Valentine et al. 1972).
Alligator diets vary by specific geographic location, habitat, prey encountered,
and prey vulnerability and size, as well as by alligator size (Barr 1994, 1997;
Delany and Abercrombie 1986; Dodson 1975; McNease and Joanen 1977; Platt et
al. 1990; Wolfe et al. 1987). For example, smaller (juvenile) alligators typically
consume invertebrates and small fish (Barr 1994, Chabreck 1971, Delany 1990,
Dodson 1975, Fogarty and Albury 1967, Giles and Childs 1949, Platt et al.
1990, Valentine et al. 1972), whereas larger adults mainly consume vertebrates
1Arthur Temple College of Forestry and Agriculture, Stephen F. Austin State University,
Nacogdoches, TX 75962. 2District 6 Wildlife Division Field Office, Texas Parks and
Wildlife Department, 1342 South Wheeler, Jasper, TX 75951. *Corresponding author -
660 Southeastern Naturalist Vol. 10, No. 4
(Delany and Abercrombie 1986, Giles and Childs 1949, McNease and Joanen
1977, Shoop and Ruckdeschel 1990).
Alligator diet studies have been concentrated in Louisiana (Platt et al. 1990,
Taylor 1986, Valentine et al. 1972, Wolfe et al. 1987), north central and central
Florida (Delany 1990, Delany and Abercrombie 1986, Delany et al. 1999, Rice
2004), and southern Florida (Barr 1994, 1997; Fogarty and Albury 1967). Such
basic, descriptive studies of alligator diet and food habits allow for speculation
about ontogenic, geographic, and temporal variation in resource utilization and
food habits for alligators throughout their geographic range (Barr 1994). Diet
analyses and food habits are essential data for understanding functional roles of
key predators in any ecosystem, but also reveal basic predator-prey relationships
and allow comparisons among individuals of different sizes and among habitats
(Barr 1994, Rice 2004). Moreover, diet can directly affect growth rates and body
condition (Chabreck 1971, McNease and Joanen 1981), which are important lifehistory
characteristics to understand when establishing management strategies. As
such, food-habit data are important for identifying and isolating possible causes for
geographic variation in growth rates and body condition among alligator populations.
However, no dietary studies have been performed in the western portion of
the American Alligator’s geographic range. Previous work from east Texas inland
wetlands has shown that alligators exhibit faster growth rates and poorer body condition
than most other populations throughout their range (Saalfeld 2010, Saalfeld
et al. 2008, Webb 2005). Therefore, quantifying diets regionally could elucidate
potential causes for regional discrepancies in growth rates and body condition.
The objectives of this study were to quantify food habits of inland alligators within
three wetlands in east Texas and determine any potential variability in dietary habits
between sexes and as a function of size or location.
Field Site Description
This research was conducted on three freshwater wetlands in east Texas: Angelina-
Neches/Dam B Wildlife Management Area (Dam B WMA), Kurth Lake, and
Little Sandy National Wildlife Refuge (NWR) (Fig. 1). Study sites were arranged
along a longitudinal gradient throughout east Texas (Fig. 1) and were selected
based upon presence of suitable habitats (i.e., mosaic of open water, floating vegetation,
and emergent vegetation) for American Alligators (Webb 2005), annual
hunts and spotlight surveys conducted by the Texas Parks and Wildlife Department
(TPWD), and landowner permission. Although study sites are representative of
most east Texas wetlands, few other wetlands within this region had adequate densities
of American Alligators to include as study sites.
Dam B WMA is a 5113-ha area located within Jasper and Tyler counties at the
confluence of the Angelina River, Neches River, and B.A. Steinhagen Reservoir.
Dam B WMA is characterized by riverine, open lake, and shallow marsh habitats,
with an average depth of 1.2 m (Webb 2005, Webb et al. 2009). Dominant aquatic
plants include Eichhornia crassipes (Mart.) Solms (Common Water Hyacinth),
Salvinia minima Baker (Common Salvinia), S. molesta D.S. Mitchell (Giant Salvinia),
Alternanthera philoxeroides (Mart.) Griseb. (Alligatorweed), Hydrilla
verticellata (L.f.) Royle (Hydrilla), Polygonum spp. (smartweed), and Nelumbo
2011 D.T. Saalfeld, W.C. Conway, and G.E. Calkins 661
lutea Willd. (American Lotus). Dominant woody species include Taxodium distichum
(L.) Rich. (Bald Cypress), Cephalanthus occidentalis L. (Buttonbush), Salix
nigra Marshall (Black Willow), Triadica sebifera (L.) Small (Chinese Tallow),
Quercus nigra L. (Water Oak), Q. lyrata Walter (Overcup Oak), Nyssa aquatica L.
(Water Tupelo), and Pinus spp. (pine species) (Godfrey and Wooten 1981).
Kurth Lake is a 294-ha reservoir located in Angelina County, comprised
of an abundance of deep (i.e., maximum depth of 12.2 m and average depth
of 2.4 m) open-water habitat (80.5% is deep open water) and a few shallow
bays with isolated pockets of emergent marsh (Saalfeld 2010). Dominant
aquatic species include American Lotus, Hydrilla, Ceratophyllum demersum
L. (Coontail), and Nuphar lutea (L.) Sm. (Yellow Pond Lily). Dominant woody
species along wetland margins include Buttonbush, Black Willow, Chinese Tallow,
Water Oak, Overcup Oak, and pine (Godfrey and Wooten 1981).
Little Sandy NWR consists of 1539 ha, of which ≈1100 ha are bottomland
hardwood forest, located on the northern bank of the Sabine River in southern
Wood County. Little Sandy NWR contains four main lentic bodies: Overton
Lake, Brumley Lake, Bradford Lake, and Beaver Lake. Of these, only Brumley
Lake (an impoundment of Little Sandy Creek) and Overton Lake (an impoundment
of Jim Ned Creek) were used as study sites. Overton Lake is approximately
175 ha, and Brumley Lake is approximately 200 ha. Both are connected by
several creeks and canals, essentially making these lakes one large wetland,
hereafter referred to as Little Sandy NWR. Little Sandy NWR is characterized
Figure 1. Location of counties and study sites in east Texas used to study food habits of
American Alligators (Alligator mississippiensis), 2006–2008.
662 Southeastern Naturalist Vol. 10, No. 4
primarily by shallow marsh with little open water or creek channels (i.e., average
depth of 0.8 m). Dominant aquatic species include Limnobium spongia (Bosc)
Rich. ex Steud. (American Frog-bit), American Lotus, Cabomba caroliniana
A. Gray (Carolina Fanwort), Coontail, Zizaniopsis miliacea (Michx.) Döll and
Asch. (Giant Cutgrass), and Yellow Pond Lily. Woody species include Chinese
Tallow, Buttonbush, Black Willow, and Morella cerifera (L.) Small (Southern
Wax Myrtle) (Godfrey and Wooten 1981).
Capture and handling
From May–October 2006, 2007, and 2008, we captured, uniquely marked,
and released American Alligators at Dam B WMA, Kurth Lake, and Little Sandy
NWR using several capture techniques (i.e., snake tongs, pole snares, by hand,
and swim-in live traps; see Saalfeld et al.  and Webb  for complete
capture descriptions). At night, spotlights affixed with red filters were used to
locate alligators with a 4.9-m Go-Devil® boat outfitted with a 20-hp Go-Devil®
mud motor. Alligators <125.0 cm in total length (TL) were captured using snares,
tongs, or hands, while swim-in live traps (Ryberg and Cathey 2004) were used to
capture larger alligators (>160.0 cm).
Upon capture, alligators were restrained with duct tape, and each individual
was sexed by cloacal examination (Chabreck 1963, Joanen and McNease 1978).
For all captured individuals (regardless of size), we measured the following
morphological features: total length (cm; ventral tip of snout to tip of tail), snout–
vent length (cm; ventral tip of snout to proximal tip of vent), eye to nare length
(cm), total head length (cm; dorsal tip of snout to distal part of head scute), tail
girth (cm; circumference of tail directly behind rear legs), right hind leg length
(cm), chest girth (cm; circumference of chest directly behind front legs), and
mass (kg). All length measurements were obtained using a flexible tape measure,
and mass was obtained using a Pesola® hanging scale (Baar, Switzerland).
We obtained diet samples from alligators ranging in size from 94.7–386.0 cm in
TL. After capture, we fastened alligators ranging in size from 106.0–244.0 cm (i.e.,
alligators <106.0 cm TL were too small, and alligators >244.0 cm TL were too large
to safely and/or effectively collect diet samples using the hose-Heimlich method)
to a plywood board and placed them at an incline with jaws secured open with a
piece of PVC pipe and duct tape. We then utilized the hose-Heimlich method (Barr
1994, Fitzgerald 1989, Rice et al. 2005) to remove all stomach contents, by carefully
inserting a Teflon hose down the esophagus and into the alligator’s stomach.
An external mark for the distance the Teflon hose was inserted into the esophagus/
stomach corresponded to the fourth whirl of scutes anterior to the hind legs (Rice
2004, Rice et al. 2005). A bilge pump connected to a garden hose was then connected
to the Teflon hose in the alligator’s stomach, and water was pumped (≈50 L/min)
into the stomach until full. With the hose still in place, a mixture of stomach contents
and water was then expelled into a collection basin. We continued this procedure
until the water flushing the stomach was clear and free of any particulate matter. We
2011 D.T. Saalfeld, W.C. Conway, and G.E. Calkins 663
then poured each stomach content sample through a 0.5-mm mesh sieve, placed the
sample into a labeled plastic bag, and stored at -20 °C for subsequent identification.
A 0.5-mm mesh sieve was selected as it retained all food items, but allowed for mud
and other particulates to flow through the sieve without clogging.
We also obtained diet samples (i.e., whole stomachs) of alligators >244 cm
in TL from harvested individuals during the TPWD’s annual alligator harvest at
Dam B WMA. Individuals were harvested by hook and line baited with chicken.
Prior to sieving, baits were removed from stomach contents, as they were easily
recognizable (i.e., harvested alligators did not have time to digest the chicken,
and usually chicken was still attached to the hook). Similar to those obtained
from the hose-Heimlich method, all stomach contents were poured through a 0.5-
mm mesh sieve, placed into a labeled plastic bag, and stored at -20 °C. Because
the hose-Heimlich method is nearly 100% effective in removing all food contents
from an alligator’s stomach (Barr 1994, Fitzgerald 1989, Rice et al. 2005), diet
samples from whole stomachs were directly compared with diet samples from the
hose-Heimlich in all analyses.
We first obtained total wet mass (g) of all stomach contents and then sorted diet
samples into identifiable prey items (e.g., fish, reptiles, mammals, birds, amphibians,
gastropods, insects, crustaceans, or bivalves) and non-prey items (e.g., rocks,
plant material, artificial objects, etc.) and identified the prey items to lowest possible
taxa. We determined minimum number of individuals based upon the occurrence of
specific items (e.g., fish otolith, water bug thoraxes, etc.). Along with occurrence, we
obtained wet masses for each taxon within a given stomach sample. All prey items
that were unidentifiable down to species were sorted into categories (e.g., fish, bird,
insect mammal, and amphibian/reptile) and included in relevant analyses.
We used a chi-square analysis (PROC FREQ; SAS Institute 1999) to examine
variation in prey presence/absence (i.e., fish, amphibians/reptiles, mammals,
birds, and invertebrates) between or among wetlands, sexes, and sizes (breeding
size [>183.0 cm TL] and non-breeding size [<183.0 cm TL]; Giles and Childs
1949, Joanen and McNease 1975, Klause 1984, McIlhenny 1934). Because most
large alligators were from Dam B WMA, no large-size comparisons were made
among wetlands. Additionally, we used an analysis of variance (ANOVA, PROC
GLM; SAS Institute 1999) to examine differences in percent composition of
prey items by wet mass (i.e., proportion [%] a prey taxon mass comprised of the
total mass of a sample) and percent occurrence (i.e., proportion [%] a single prey
item comprised of the total number of prey items within a diet sample) between
or among sizes, sexes, and wetlands. We could not examine interactions among
these variables (i.e., sex, size class, and wetland) due to sample-size limitations.
An alpha level of 0.05 was used for these analyses, and least squared means separation
was used to examine differences (P < 0.05).
From 1 June 2006–31 September 2008, we obtained a total of 62 American
Alligator diet samples (24 from Dam B WMA, 35 from Little Sandy NWR, and
664 Southeastern Naturalist Vol. 10, No. 4
3 from Kurth Lake; Table 1). We obtained samples from alligators ranging in
size from 94.7 cm to 386.0 cm TL. The majority of the diet samples (49) were
obtained non-lethally using the Hose-Heimlich technique, while fewer (13)
were obtained from harvested alligators collected during hunts conducted at
Dam B WMA in 2007 (n = 9) and 2008 (n = 4).
Although many prey items were damaged (i.e., presumably due to digestion,
jaw pressure, and/or prey capture), we identified a total of 33 different prey taxa
(comprising 670 individual prey items) and 1 parasite (Table 2). Irrespective of
size class, sex, and wetland, 47.8% of individual prey items identified were giant
water bugs (Belostomatidae), with one or more giant water bug documented
in 66.0% of all samples. Nearly all (97.3%) samples contained organic by-catch
(e.g., woody debris, aquatic plants, seeds, etc.), whereas 52.3% of samples contained
rocks/stones and 19.1% contained foreign matter (e.g., plastic bottle caps,
fishing tackle, tent spike, shotgun shell). Additionally, 53.0% of all samples had
at least 1 parasite.
Invertebrates, fish, birds, mammals, and amphibians/reptiles occurred equally
between males and females (P > 0.05). Invertebrates, fish, birds, and amphibians/
reptiles occurred at similar frequencies among wetlands (P > 0.05); however,
mammals occurred more often in alligator diets at Dam B WMA than at other
wetlands (Table 3). Irrespective of wetland, invertebrates occurred more often
in non-breeding than breeding-size alligators (Table 4). Conversely, mammals
and amphibians/reptiles occurred more often in breeding-size alligator’s diets,
whereas birds and fish occurred in both size classes equally (Table 4).
Irrespective of size, wetland, and sex, percent composition (by wet mass) was
48.2% food and 51.8% non-food (e.g., stones/rocks, plastic, woody debris, etc.).
Overall, percent composition by wet mass of invertebrates, fish, birds, mammals,
and amphibians/reptiles (P > 0.05) was similar between male and female
alligators. Additionally, percent composition by wet mass of invertebrates, fish,
amphibians/reptiles, birds, and mammals was similar among wetlands (Table 5).
However, similar to frequency of food items, percent composition by wet mass
for breeding-size alligators contained a greater percentage of vertebrates (mean
= 42.7%) as compared to non-breeding-size alligators (mean = 25.7%). Additionally,
breeding-size alligators consumed more mammals by wet mass (Table 6)
than smaller alligators. Both size classes contained similar percent composition
Table 1. Sample size (n), average mass (kg), average length (cm), and sex for American Alligators
(Alligator mississippiensis) in which diet samples were obtained by month from Angelina-Neches/
Dam B Wildlife Management Area, Kurth Lake, and Little Sandy National Wildlife Refuge, TX,
Month n mass (kg) length (cm) Males Females
June 13 7.5 133.5 3 10
July 16 9.8 132.1 10 6
August 16 6.8 131.5 12 4
SeptemberA 17 51.8 215.6 13 4
AAlligator harvests occurred only in September resulting in larger average mass and length measurements
for this month.
2011 D.T. Saalfeld, W.C. Conway, and G.E. Calkins 665
Table 2. Food items documented in American Alligator (Alligator mississippiensis) stomach content
samples (identified to lowest possible taxon) from Angelina-Neches/Dam B Wildlife Management
Area (DMB), Kurth Lake (Kurth), and Little Sandy National Wildlife Refuge (LSNWR), TX,
Taxon DMB LSNWR Kurth
Unionidae (freshwater mussel) X X X
Cestoda (tapeworm) X X
Clitellata (leech) X X
Palaemonidae (freshwater shrimp) X
Cambaridae (crayfish) X X X
Lestidae (spreadwing damselfly) X X
Aeshnidae (dragonfly) X X
Orthoptera (grasshopper) X X
Nepidae (water scorpion) X X
Belostomatidae (giant water bug) X X
Coleoptera (beetle) X X X
Gyrinidae (whirligig beetle) X
Psephenidae (water penny) X
Tipulidae (cranefly larva) X X
Pisauridae (fishing spider) X X
Lepisosteus oculatus Winchell (Spotted Gar) X X
Cyprinella lutrensis Baird and Girard (Red Shiner) X
Fundulus spp. Lacèpéde (Top Minnow) X
Gambusia affinis Baird and Girard (Western Mosquitofish) X X
Lepomis gulosus Cuvier (Warmouth) X
Lepomis macrochirus Rafinesque (Bluegill) X X
Lepomis miniatus Jordan (Redspotted Sunfish) X
Micropterus salmoides Lacèpéde (Largemouth Bass) X
666 Southeastern Naturalist Vol. 10, No. 4
Table 2, continued.
Taxon DMB LSNWR Kurth
Hyla cinerea Schneider (Green Tree fFrog) X
Kinosternon flavescens Agassiz (Yellow Mud Turtle) X
Trachemys scripta Wied-Neuwied (Red-eared Slider) X X
Nerodia spp. Baird and Girard (unidentified water snake) X X
Agkistrodon piscivorus Lacèpéde (Water Moccasin) X X
Alligator mississippiensis Daudin (Alligator) X
Anhinga anhinga L. (Anhinga) X
Bubulcus ibis L. (Cattle Egret) X
Gallinula chloropus L. (Common Moorhen) X
Myocastor coypus Molina (Nutria) X
Sus scrofa L. (Feral Hog) X
Table 3. Presence/absence (n), chi-square (χ2), and P-values resulting from chi-square analysis of
invertebrate, fish, amphibian/reptile, bird, and mammal prey item frequency among wetlands for
American Alligators (Alligator mississippiensis) at Angelina-Neches/Dam B Wildlife Management
Area (Dam B WMA), Kurth Lake, and Little Sandy National Wildlife Refuge (LSNWR), TX,
Dam B WMA Kurth Lake LSNWR
Variable Present Absent Present Absent Present Absent χ2 P
Invertebrates 10 1 3 0 30 3 0.30 0.862
Fish 5 6 2 1 17 16 0.43 0.805
Amphibians/reptiles 3 8 1 2 6 27 0.69 0.710
Birds 1 10 0 3 9 24 2.49 0.287
Mammals 3 8 0 3 1 32 6.53 0.038*
2011 D.T. Saalfeld, W.C. Conway, and G.E. Calkins 667
by wet mass of fish, amphibians/reptiles, and birds (Table 6). However, diets of
smaller alligators had greater percent composition by wet mass of invertebrates
than breeding-size alligators (Table 6).
Males and females had similar percent occurrence of invertebrates, fish, amphibians/
reptiles, birds, and mammals (P > 0.05). Among wetlands, alligators
also had similar percent occurrence of invertebrates, fish, amphibians/reptiles,
birds, and mammals (Table 7). Similar to previous analyses, a greater percentage
of invertebrate prey items were detected within non-breeding-size alligator diets
(Table 8) when compared to breeding-size alligators, and breeding-size alligators
had a greater percentage of amphibians/reptiles and mammals in their diet
samples than non-breeding-size alligators (Table 8). Both size classes had similar
percentages of birds and fish within their diet samples (Table 8).
American Alligators exhibit an extremely varied diet, as evidenced by their
opportunistic strategy of exploiting locally available and/or abundant prey. Many
studies have documented alligator prey encompassing a wide diversity of sizes
and taxa, from small insects and crustaceans to large vertebrates (Chabreck 1971,
Delany and Abercrombie 1986, Rice 2004, Valentine et al. 1972, Wolfe et al.
Table 4. Presence/absence (n), chi-square (χ2), and P-values resulting from chi-square analysis of
invertebrate, fish, amphibian/reptile, bird, and mammal prey item frequency between size classes
(breeding: >183.0 cm in total length, non-breeding: less than 183.0 cm in total length) for American Alligators
(Alligator mississippiensis) at Angelina-Neches/Dam B Wildlife Management Area, Kurth
Lake, and Little Sandy National Wildlife Refuge, TX in 2006–2008.
Variable Present Absent Present Absent χ2 P
Invertebrates 43 4 9 6 8.34 0.004*
Fish 24 23 8 7 0.02 0.878
Amphibians/reptiles 10 37 8 7 5.67 0.017*
Birds 10 37 1 14 1.66 0.197
Mammals 4 43 7 8 11.34 0.001*
Table 5. Means, standard errors (SE), and F and P-values resulting from analysis of variance of percent
(%) composition by wet mass of invertebrate, fish, amphibian/reptile, bird, and mammal prey
items for American Alligators (Alligator mississippiensis) among wetlands (Angelina-Neches/
Dam B Wildlife Management Area [Dam B WMA], Kurth Lake, and Little Sandy National Wildlife
Refuge [LSNWR]), TX, 2006–2008.
Dam B WMA Kurth Lake LSNWR
Variable Mean (%) SE Mean (%) SE Mean (%) SE F P
Invertebrates 15.7 5.3 34.6 18.6 16.7 3.4 0.93 0.402
Fish 5.9 4.2 0.8 0.8 10.2 2.8 0.68 0.513
Amphibians/reptiles 11.9 5.1 26.0 26.0 0.3 0.1 1.43 0.248
Birds 0.0 0.0 0.0 0.0 11.3 4.6 2.28 0.111
Mammals 11.4 5.4 0.0 0.0 2.0 2.0 1.94 0.153
668 Southeastern Naturalist Vol. 10, No. 4
1987). Alligator food habits in this study mirrored those observed in previous
studies, in that alligators appear to forage opportunistically, and in the feeding
process, often ingest relatively large quantities of non-food items. Although most
food habit studies documented similar vertebrate prey items (i.e., amphibians/
reptiles, mammals, and fish; Barr 1994,1997; Delany and Abercrombie 1986;
Table 6. Means, standard errors (SE), and F and P-values resulting from analysis of variance of percent
(%) composition by wet mass of invertebrate, fish, amphibian/reptile, bird, and mammal prey
items between size classes (breeding: >183.0 cm in total length, non-breeding: <183.0 cm in total
length) for American Alligators (Alligator mississippiensis) at Angelina-Neches/Dam B Wildlife
Management Area, Kurth Lake, and Little Sandy National Wildlife Refuge, TX, 2006–2008.
Variable Mean (%) SE Mean (%) SE F P
Invertebrates 21.5 3.6 3.5 1.8 7.80 0.007*
Fish 8.0 2.2 8.2 6.7 0.00 0.967
Amphibians/reptiles 7.6 3.0 14.6 6.7 1.17 0.283
Birds 8.4 3.5 0.0 0.0 1.85 0.178
Mammals 1.8 1.5 17.2 8.4 8.29 0.006*
Table 7. Means, standard errors (SE), and F and P-values resulting from analysis of variance of
percent (%) occurrence of invertebrate, fish, amphibian/reptile, bird, and mammal prey items for
American Alligators (Alligator mississippiensis) among wetlands (Angelina-Neches/Dam B Wildlife
Management Area [Dam B WMA], Kurth Lake, and Little Sandy National Wildlife Refuge
[LSNWR]), Texas, 2006–2008.
Dam B WMA Kurth Lake LSNWR
Variable Mean (%) SE Mean (%) SE Mean (%) SE F P
Invertebrates 52.0 8.4 70.0 6.9 68.5 5.0 1.75 0.183
Fish 16.6 5.7 18.9 11.6 14.6 3.2 0.08 0.920
Amphibians/reptiles 14.7 5.3 11.1 11.1 6.9 3.2 0.93 0.401
Birds 2.1 1.4 0.0 0.0 7.1 3.3 0.92 0.406
Mammals 14.6 5.7 0.0 0.0 2.9 2.9 2.25 0.115
Table 8. Means, standard errors (SE), and F and P-values resulting from analysis of variance of
percent (%) occurrence of invertebrate, fish, amphibian/reptile, bird, and mammal prey items
between size classes (breeding >183.0 cm total length, non-breeding <183.0 cm total length) for
American Alligators (Alligator mississippiensis) at Angelina-Neches/Dam B Wildlife Management
Area, Kurth Lake, and Little Sandy National Wildlife Refuge, TX, 2006–2008.
Variable Mean (%) SE Mean (%) SE F P
Invertebrates 71.7 4.3 32.7 1.8 18.72 <0.001*
Fish 12.7 2.6 24.4 6.7 3.13 0.082
Amphibians/reptiles 6.6 2.7 21.1 6.7 5.41 0.024*
Birds 5.8 2.5 1.7 0.0 0.83 0.365
Mammals 3.2 2.2 20.1 8.4 7.34 0.009*
2011 D.T. Saalfeld, W.C. Conway, and G.E. Calkins 669
McNease and Joanen 1977), food availability estimates are difficult to obtain due
to the diversity of prey items consumed and the apparently very generalized opportunistic
foraging strategy employed by alligators, regardless of region. Such
constraints make it difficult to estimate specific food selectivity or preferences,
where any geographic differences in food habits are most likely influenced by
food availability, rather than species-specific selection processes (Barr 1994,
1997; Delany and Abercrombie 1986; McNease and Joanen 1977).
In this study, fish were the most prevalent vertebrates in diet samples; however,
most fish were found in samples from Little Sandy NWR, where over 70%
of samples in which fish were present were from this study site. Although fish
have short residence times in alligator digestive systems (Barr 1997, Rice 2004),
they still occurred in diet samples more frequently than other vertebrates (that
have longer residence time), indicating that fish may be the most important, or
most available, vertebrate prey item for all size classes at Little Sandy NWR.
Conversely, fish were less prevalent in the samples from Dam B WMA (25.0%
of diet samples contained fish) and Kurth Lake (4.8% of diet samples contained
fish). At Dam B WMA, fewer fish were available due to an extended water drawdown
event occurring during 2006 and 2007 for repairs to the primary dam. This
drawdown lasted over a year and substantially reduced the abundance of both fish
and other aquatic vertebrates (e.g., turtles; Bill Adams and Gary Calkins, Texas
Parks and Wildlife Department, Jasper, TX, pers. comm.). After repairs were
completed and water levels returned to normal pool level, many exotic invasive
plant species such as Alligatorweed, Giant Salvinia, and Water Hyacinth became
re-established, expanded areal extent, and increased their densities throughout
the study site. These exotic invasive plants formed thick mats, and appeared to
both reduce alligator movements and limit their access to shallow water habitat
where alligators tend to feed more efficiently (Saalfeld 2010). Decreased fish
abundances after the drawdown likely forced alligators to focus on alternative
prey items, such as mammals and other alligators. As cannibalism was only documented
at Dam B WMA after the drawdown, it likely resulted when low water
levels and subsequent expansion of exotic invasive plant species led to unusually
high concentrations of alligators of all size classes.
Despite generally being opportunistic, alligators appear to shift diets from invertebrates
to vertebrates as they increase in size, a phenomenon documented in
many studies (Barr 1997, Chabreck 1971, Delany and Abercrombie 1986, Delany
et al. 1999, Giles and Childs 1949, McIlhenny 1935, McNease and Joanen 1977,
Taylor 1986, Valentine et al. 1972, Wolfe et al. 1987). Specifically, within this
study, mammals and amphibians/reptiles occurred most often in diets of larger
alligators (>183.0 cm), whereas insects, crayfish, and small fish occurred most
often in diets of smaller alligators (i.e., <183.0 cm). However, insects may be
over-represented in crocodilian diet samples due to longer residence times of
exoskeletons and secondary ingestion (Barr 1994, 1997; Garnett 1985; Jackson
et al. 1974; Wolfe et al. 1987). Additionally, after the drawdown at Dam B WMA,
these species are likely the first to re-colonize, leading to their greater frequencies
in diet samples. Because they occurred at similar frequencies among wetlands,
these are all important food items for alligators in east Texas, especially for smaller
670 Southeastern Naturalist Vol. 10, No. 4
size classes. As alligators increase in size, they become more capable (i.e., due to
changes in ontogenetic skull structure) of exploiting larger food resources (Delany
1990, Delany et al. 1999, Dodson 1975), but also have greater energy requirements
and metabolic costs (Dodson 1975, Thorbjarnarson 1993). Therefore, shifting to
larger prey items meets increased energy demands (Delany et al. 1999) and maximizes
feeding efficiency for larger alligators (Wolfe et al. 1987). Because alligators
shift to larger prey items as they increase in size, the prevalence of mammals in diet
samples from Dam B WMA could be due to the average size of alligators sampled
(Shoop and Ruckdeschel 1990), rather than other compounding factors such as the
drawdown and food availability.
Overall, alligators within these study sites exhibit faster growth rates, but are
in poorer condition (i.e., alligators weigh less than alligators of similar lengths)
compared to alligators in other geographic regions (Saalfeld 2010, Saalfeld et al.
2008). Although the role of food availability on alligator growth and condition
is difficult to assess, it is likely an important factor influencing geographic variation
in growth rates and condition. For example, the water drawdown and rapid
expansion of exotic invasive species at Dam B WMA could have reduced prey
abundances and/or availability, causing a reduction in body condition of resident
alligators. Moreover, the abundance of open water habitat at Kurth Lake could
have limited prey diversity and availability resulting in both slower growth rates
and poorer condition. Little Sandy NWR contained abundant sources of fish
and wading birds (numerous vegetated islands for rookeries); however, many
of these prey items were not always available. For example, only young wading
birds (which most likely fell out of nests) were found in diet samples. Wading
birds synchronize nesting and migration, resulting in only a short time span when
these prey items are available to alligators. Additionally, other large vertebrate
prey items (e.g., mammals) may not occur in high densities within this wetland
due to its small size (375 ha) and control management efforts exerted to reduce
their density. Therefore, relying mainly upon fish and seasonally available wading
birds may result in the poor condition of alligators observed in this study
site. In addition to food availability, the high percentage of non-food by-catch
documented during this study could be an indicator of reduced feeding efficiency
within these wetlands. No studies have reported such high percentage composition
of non-food items (Fogarty and Albury 1967, Platt et al. 1990). Although we
did not find a correlation between percentage of non-food by-catch and condition
(D.T. Saalfeld et al., unpubl. data), it is possible that habitat conditions such as
reduced water clarity or increased vegetation density (both of which were documented
within these wetlands) could influence feeding efficiency and, ultimately,
To date, few studies have focused on inland American Alligators, especially in
Texas. This study supports the notion that faster grow rates and poorer condition
of alligators within this region (Saalfeld et al. 2008) could potentially be attributed
to food availability. To better manage these populations, future work should
assess abundances and nutritive quality of dominant prey items (e.g., mammals,
amphibians/reptiles, fish, wading birds, and invertebrates). As diets tend to
mirror prey abundances (Barr 1994, 1997; Delany and Abercrombie 1986; Mc-
Nease and Joanen 1977), changes in prey populations (e.g., fish kills following
2011 D.T. Saalfeld, W.C. Conway, and G.E. Calkins 671
drawdown), may result in lower quality prey (e.g., invertebrates and small fish)
being consumed. Therefore, understanding food availability and quality could
provide insights into selection patterns influencing growth rates and condition.
Financial, logistical, and technical support was provided in part by the Texas Parks
and Wildlife Department, and the Arthur Temple College of Forestry and Agriculture,
Stephen F. Austin State University. Special appreciation to the staff of Martin Dies, Jr.
State Park, US Fish and Wildlife Service, Jim Neal, and Abitibi Consolidated Industries,
for additional logistical, financial, and technical support. We thank C. Comer, I. Hung,
M. Kwiatkowski, and D. Scognamillo for comments and reviews on previous versions of
this manuscript. Finally, we thank Ragan White, Allen Rainey, Ben Koerth, Jerry Staton,
Austin Wadyko, Matt Buckingham, Jake Rustin, Brandon McNeill, and Sarah Saalfeld
for assisting with data collection for this study.
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