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Predation and Scavenging by American Alligators on Whooping Cranes and Sandhill Cranes in Florida
Martin J. Folk, Allan R. Woodward, and Marilyn G. Spalding

Southeastern Naturalist, Volume 13, Issue 1 (2014): 64–79

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Southeastern Naturalist M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 64 2014 SOUTHEASTERN NATURALIST 13(1):64–79 Predation and Scavenging by American Alligators on Whooping Cranes and Sandhill Cranes in Florida Martin J. Folk1,*, Allan R. Woodward2, and Marilyn G. Spalding3 Abstract - We documented 15 cases of Grus americana (Whooping Crane) mortality in 6 Florida counties during 1997–2010 that may have been associated with Alligator mississippiensis (American Alligator; hereafter Alligator) predation or scavenging. In four cases, Whooping Crane remains were identified within Alligator mouths or stomachs. The latter is a first in the literature. Other cases were less conclusive but suggestive that Alligators were involved with predation or scavenging of Whooping Cranes. An Alligator was videotaped eating the eggs of G. canadensis pratensis (Florida Sandhill Crane), plus Alligators were implicated in the depredation of eggs from another Sandhill Crane nest and a Whooping Crane nest; the latter was the first record of Alligators depredating Whooping Crane eggs. All 4 populations of Whooping Cranes and 4 populations of Sandhill Cranes in the southeastern United States spend at least part of the year within the range of Alligators. To improve survival of cranes in areas where water management is practiced, water depths should be maintained at optimal levels (10–20 cm) for crane nesting and roosting to discourage intrusion by larger Alligators and to allow the cranes to detect approaching Alligators. Introduction Alligator mississippiensis (Daudin) (American Alligator; hereafter Alligator), Grus americana (L.) (Whooping Crane), and G. canadensis (L.) (Sandhill Crane) share wetland habitats in the southeastern United States, yet little has been published concerning predation by Alligators on cranes. Alligators are opportunistic carnivores that occasionally prey on wading birds (Giles and Childs 1949, McNease and Joanen 1977, Rice et al. 2007, Valentine et al. 1972), but food-habit studies indicate that wading birds are a minor part of their diet. Neither Sandhill Cranes nor Whooping Cranes have been identified in stomach contents in studies of Alligator food habits in Florida (Barr 1997, Delany and Abercrombie 1986, Delany et al. 1999, Rice et al. 2007). Alligators have been identified as a predator on Porphyrio martinicus L. (Purple Gallinule) eggs (Giles and Childs 1949) and as a major predator on Branta canadensis (L.) (Canada Goose) eggs (Chabreck and Dupuie 1976) in Louisiana. In Florida, however, no bird eggs have been identified in food-habit studies (Barr 1997, Rice et al. 2007), suggesting that egg predation by Alligators is uncommon there. 1Florida Fish and Wildlife Conservation Commission, 1475 Regal Court, Kissimmee, FL 34744. 2Florida Fish and Wildlife Conservation Commission, 1105 SW Williston Road, Gainesville, FL 32601. 3Department of Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida, Box 110880, Gainesville, FL 32610. *Corresponding author - marty.folk@myfwc.com. Manuscript Editor: Scott Markwith Southeastern Naturalist 65 M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 Allen (1952), in his monograph on Whooping Cranes, did not mention Alligators as potential predators of Whooping Cranes. Nor do species accounts of Whooping and Sandhill Cranes (Lewis 1995, Tacha et al. 1992) mention Alligators as predators. Likewise, management plans such as those for the eastern population of Sandhill Cranes (Ad Hoc Eastern Population Sandhill Crane Committee 2010) and the eastern migratory Whooping Cranes (Wisconsin Department of Natural Resources 2006) make no mention of Alligators. Bennett and Bennett (1990a, b) described Alligators preying on G. c. pratensis (F.A.A. Meyer) (Florida Sandhill Cranes) and their eggs in the Okefenokee Swamp of Georgia. Alligators depredated one nest and killed a 50-day-old prefledged chick and subadult crane. Thompson (1970) noted that Florida Sandhill Cranes nesting at the Loxahatchee National Wildlife Refuge (northern edge of the Everglades) often nested within 100 m of active Alligator dens and that several nests had been built within a few meters of active Alligator trails, but he did not discuss the significance of these observations. Butler (2009) documented an Alligator depredating eggs of a G. c. pulla Aldrich (Mississippi Sandhill Crane). John James Audubon (1838) portrayed the Whooping Crane apparently about to prey on Alligator hatchlings (Fig. 1). Ironically, we describe Alligators preying on cranes. The endangered Whooping Crane is an iconic symbol of the recovery of an endangered species, having progressed from a minimum of 21 individuals in 1954 (CWS and USFWS 2007) to almost 600 birds today (W.B. Brooks, USFWS, Jacksonville, FL, pers. comm.). All 4 wild populations of Whooping Cranes are sympatric with Alligators for at least part of their life cycle. The only self-sustaining population breeds in and adjacent to Wood Buffalo National Park in Canada and winters in and adjacent to the Aransas National Wildlife Refuge on the Gulf Coast of Texas (Aransas-Wood Buffalo Population [AWBP]). This population has grown to >250 individuals (USFWS 2012). Whooping Cranes were raised in captivity and released into Florida during 1993–2006 in an effort to establish a nonmigratory population (Folk et al. 2010). Efforts there to create a self-sustaining population have been hampered by excessive mortality and low productivity (Spalding et al. 2010); consequently, releases were discontinued in 2006. Migratory Whooping Cranes were reintroduced in the eastern United States beginning in 2001 (Urbanek et al. 2010); this project is ongoing. A third reintroduction of nonmigratory Whooping Cranes was initiated in Louisiana in 2010 (LADWF 2010). Four populations of Sandhill Cranes also occur within the range of the American Alligator. Two migratory populations include the midcontinent population that winters primarily in Texas (Tacha et al. 1992) and the eastern population that winters primarily in Florida and southern Georgia (Ad Hoc Eastern Population Sandhill Crane Committee 2010). Two nonmigratory populations of Sandhill Cranes in the southeast are in Mississippi and in Florida and southern Georgia. Mississippi Sandhill Cranes are listed as federally endangered (Gee and Hereford 1995); Florida Sandhill Cranes occur in Florida and southern Georgia and are state-listed as threatened (State of Florida 2012). Southeastern Naturalist M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 66 Figure 1. Whooping Crane preparing to eat small alligators, painting by John James Audubon. The Birds of America, Vols. I–IV, Special Collections, courtesy of the University Library System, University of Pittsburgh. Southeastern Naturalist 67 M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 During several decades of intensive studies of Whooping and Sandhill Cranes in Florida, we accumulated observations of Alligators preying on these species and their eggs. In this paper, we summarize our cases for Florida and those of investigators in other southeastern states. Finally, we discuss the impacts of Alligators on reintroduced and natural populations of Whooping and Sandhill Cranes. Field-Site Description We include information from regions in the Southeast in which the ranges of Alligators and cranes (Whooping and Sandhill) overlap. This area extends from coastal Texas to Georgia and Florida. We collected most of our data in the northern half of peninsular Florida. Methods We closely monitored Whooping Cranes in central Florida from 1993 through 2012. Each bird was checked visually daily (aided by VHF telemetry) for the first 3–6 months following release and 2–3 times each week thereafter for the life of the bird (Folk et al. 2010). We necropsied dead birds to determine the cause of death, general health condition, and level of disease and parasites. The primary predator of Whooping Cranes in Florida has been Lynx rufus (Schreber) (Bobcat) (Nesbitt et al. 2001). Of 175 Whooping Crane mortalities where cause of death could be determined via necropsy, 95 were suspected of being killed by Bobcats (M.J. Folk and M.G. Spalding, unpubl. data). Diagnostic characteristics of Bobcat predation on Whooping Cranes were: the base of the neck broken and spinal cord severed by biting, flesh mainly eaten from the pectoral muscle, carcass dragged from the kill site to cover usually in upland (not wetland) habitats, and remains covered with vegetation or soil. There was no evidence of biting of transmitters or bands among the remains of cranes identified as killed by Bobcats. In contrast, for the only other predator identified as preying on Whooping Cranes, the American Alligator, bite marks on the birds’ bands and transmitters were common. Whooping Cranes mortality incidents did not occur within the range of Ursus americanus floridanus Merriam (Florida Black Bear) or Puma concolor coryi Bangs (Florida Panther); Canis latrans Say (Coyote) was a potential predator, but we did not document diagnostic evidence of predation by Coyotes (M.J. Folk and M.G. Spalding, unpubl. data) For this paper, we reviewed necropsy reports and records and summarized cases involving suspected predation or scavenging by Alligators. We did not directly observe Alligators preying on cranes or other large wading birds, nor are we aware of such observations documented in the literature. However, evidence suggests Alligators prey on cranes, and we assumed the following, based on general Alligator predatory behavior: • Predatory Alligators would have to be ≥1.2 m in total length (TL) to effectively injure or kill a full-grown crane. Southeastern Naturalist M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 68 • Alligators probably do not actively feed when water temperatures are <15.5 °C (Joanen and McNease 1971), as they usually are from mid-December through February in central Florida. Exceptions to this pattern would be extended warm fronts during the winter. • Water levels at predation sites would have to be ≥20 cm deep to allow Alligators to be fully or partly submerged while effectively stalking or ambushing cranes. • Alligators would prey on cranes in water or on a shoreline near water, but not on dry land more than 3 m from the shoreline, where cranes would be likely to detect their presence. Contrary to popular belief and conjecture that they effectively hunt on land (Dinets 2010), Alligators are awkward on land and have not been documented to stalk and attack free-roaming birds on land. Full-grown cranes are alert when foraging on land and would be difficult for predators to approach. Bobcats stalk cranes and use a burst of speed to pounce on them. • Because cranes rarely wade in depths of water that would touch their feathers, most predation attempts would be in shallow (<46 cm) water. • An Alligator would first seize a crane by one or both legs or, less likely, the lower torso or head during predation. • A crane would likely sustain leg injuries while struggling against an Alligator that had seized its leg. An Alligator would likely twist the leg as they shake their head or rotate their body during predation. • Once the crane was secured, an Alligator would bite and crush the crane’s body until it was subdued (Busbey 1989). It might also hold the crane under water until it drowned (McIlhenny 1935). • After the crane was killed, an Alligator would manipulate the crane into a position where it could crush the bones of the crane in preparation for swallowing (Buseby 1989). Smaller (1.2–3 m TL) Alligators would first feed on appendages, the head, or the neck, so it is likely that cranes that were not completely consumed would be missing appendages. Very large Alligators (>3 m TL) could swallow an entire crane. We regarded the following diagnostic characteristics of a kill as consistent with Alligator predation or scavenging: • remains of cranes found in or near water deeper than what cranes in Florida normally use (i.e., ≥46 cm deep); • twisting of appendages or neck consistent with Alligator feeding behavior; • dismemberment/amputation of appendages, head, or neck; • tooth marks in radio transmitters, bird bands, or remains; • presence of Alligators near remains; and • presence of Whooping Crane parts in stomachs of Alligators trapped at mortality sites. As part of a comprehensive study of nesting Sandhill and Whooping Cranes in Florida, we employed video surveillance cameras, temperature-logging artificial eggs, and camera traps during the breeding seasons of 2010–2012. Our goals for this research were to determine what species of predators visited nests and how Southeastern Naturalist 69 M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 cranes responded to them. We used time-lapse video-surveillance cameras to document diurnal nest attendance and detect nest disturbances; we deployed these video systems ≥100 m away from nests (to preclude disturbing the birds) within 1 day of discovery of a nest. Five to 10 days later, we deployed a temperature-logging egg in some of those nests to measure incubation temperature. These eggs, when damaged by the bites of predators, also provided evidence of predators at nests. At the time of deployment of an egg, we installed a camera trap (Reconyx PC-900 HyperFireTM Professional High Output Covert IR Camera Traps) 3–10 m from the nest to document nest disturbances and the reactions of the birds to the disturbances. Results We documented 15 cases of Whooping Crane mortality in 6 Florida counties during 1997–2010 that may have been associated with Alligator predation or scavenging (Table 1). Eight of these cranes were female and 7 were male, and they varied in age from 0.5 to 9.9 years; 1 1 of the cranes were ≤2 years of age. Most (13) of the 15 dead Whooping Cranes we attributed to Alligator predation or scavenging were part of the Florida nonmigratory population, which represented 7.4% of 175 mortalities for which cause of death could be attributed and 11.5% of the 113 mortalities for which the likely predator was identified (M.J. Folk, A.R. Woodward, and M.G. Spalding, unpubl. data). Two Whooping Crane deaths associated with Alligators were members of the eastern migratory population (Table 1). These 2 deaths represented 2.4% of 85 mortalities where cause of death could be assigned to a predator during 2001–2011 and 11.8% of mortalities in which the likely predator was identified (Whooping Crane Eastern Partnership 2012). In four cases, whooping crane remains were identified within Alligator stomachs or mouths (Table 1). Other cases were less conclusive but suggestive that Alligators were involved with predation or scavenging of Whooping Cranes. One case appeared to involve predation on Whooping Crane eggs and attempted predation on the female incubating those eggs. This bird (Bird 1008; Table 1) was observed at the time of nest failure to be missing its left leg. Even though it was missing a leg, the bird could fly. The crane was found dead the next day, probably killed by a Bobcat based on evidence from the remains. Necropsy showed that the left leg had been amputated mid-tibiotarsus. We suspect that an Alligator twisted the right leg sufficiently to break the ligament that attached it to the hip. We do not think any other predator would be capable of amputating the leg. Although it was remarkable that the bird survived the initial attack, it probably would not have survived long if it had not been killed by a Bobcat. The nest contained an artificial egg for monitoring temperature; the egg had been fractured and contained indentations consistent with an Alligator bite (Fig. 2). The marks on the egg were not like those typically made by known mammalian predators such as Procyon lotor (L.) (Raccoon). The natural egg was missing from the nest and presumably eaten by the Alligator. Southeastern Naturalist M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 70 Table 1. Bird ID, evidence of alligator predation, county of mortality, sex of bird, date of mortality, and age (yrs) at mortality of 15 Whooping Cranes that exhibited evidence of possible predation by alligators in Florida during 1997–2010. Bird ID Evidence of alligator predation or scavenging County Sex Date Age 666 Bird’s transmitter recovered from deep water of canal containing 3 large Alligators Lake F 3/22/1997 0.8 500 Bird’s transmitter in deep water, bearing teeth marks, with 2 large Alligators nearby Polk F 1/11/1999 3.7 481 Transmitter recovered from deep water under floating mat of veget ation Brevard F 6/10/1999 5.2 823 Cracked transmitter band with teeth marks; edge of deep water Lake F 7/25/1999 1.2 903 Remains along deep dugout; remains recovered from stomach of 2-m female Alligator Lake F 11/22/1999 0.5 932 Trapped local Alligator and found bird’s aluminum band in its stomach Lake M 3/6/2000 0.8 1002 Remains found in lake; twisting of tissues and crushing Polk M 4/3/2001 0.9 1029 Leg in deep water of lake with 3-m Alligator 150 m away Polk M 10/17/2001 1.4 1022 Alligator observed with crane in mouth, dropped it 12 m from shore; twisted body parts Polk M 10/20/2001 1.5 1183 Wing recovered from deep canal with Alligators present; twisted remains Polk M 4/10/2002 1.0 463 Found midmarsh, left leg missing; holes in abdominal cavity Osceola M 4/12/2004 9.9 23-051 Alligator sign at site, teeth marks on band, no usual evidence of Bobcat predation Levy M 4/1/2007 1.8 1642 Transmitter in deep pond with 11 Alligators Lake F 5/16/2008 2.0 37-08 DAR1 Transmitter signal tracked to a large Alligator confirming it had eaten at least part of Alachua F 4/11/2009 0.8 a missing crane 1008 Bird alive but missing a leg; damaged artificial egg near nest Osceola F 3/31/2010 9.9 1Wintering migratory Whooping Cranes; all others are nonmigratory. Southeastern Naturalist 71 M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 Video surveillance footage documented depredation of a Sandhill Crane nest by an Alligator (see Supplemental File 1, available online at http://www.eaglehill. us/SENAonline/suppl-files/s13-1-S2016-Folk-s1, and, for BioOne subscribers, at http://dx.doi.org/10.1656/S2016.s1). In this video, the incubating crane can be seen standing and spreading its wings in typical predator-defense posture as the Alligator nears the nest. The bold posturing of the crane fails to intimidate the oncoming Alligator, which can eventually be seen eating the eggs. We estimate this Alligator’s total length to have been 2.0–2.5 m. We documented another Sandhill Crane nest failure possibly associated with an Alligator. At this nest, camera trap images showed the incubating bird leaving the nest at 04:03:36 hrs (Fig. 3). The next images recorded by the camera trap apparently were recorded after the Alligator had left the nest and bumped the camera, triggering a picture of the departing Alligator’s tail at 06:51:57 hrs (Fig. 3). Camera traps are normally triggered by motion of an object with a temperature different from ambient temperature. We suspect the camera failed to trigger when the Alligator was at the Figure 2. Artificial egg recovered from a Whooping Crane nest. The fracturing of the egg and indentations in the surface are consistent with Alligator bites. Southeastern Naturalist M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 72 Figure 3. Camera trap images of a Florida Sandhill Crane nest before and after egg predation by an Alligator. In the second photograph, the departing Alligator’s tail is visible at the bottom center of the image (in circle). Southeastern Naturalist 73 M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 nest because the Alligator’s body temperature was close to the ambient temperature. This camera was 3 m from the nest, so the Alligator had to have been about 3 m TL for its head to have bumped the camera and for its tail to have been in the photograph of the nest. Half of the artificial egg that had been deployed in the nest to measure incubation temperature was recovered near the nest. We did not find remains of the natural egg and presume it was eaten by the Alligator. Not all attempts by Alligators to approach nests were successful. A pair of Sandhill Cranes worked together using postures and calls to intimidate an Alligator near their nest (Fig 4). We estimate that this Alligator was 1.5–2.0 m TL. This nest was successful (Fig 4). Discussion Cases of possible Alligator predation on Whooping Cranes in our study were based primarily on evidence at kill sites and from necropsies. We cannot be certain that all birds listed in Table 1 were killed by an Alligator. Some birds may have been scavenged but not killed by the Alligator. Evidence of hemorrhaging from a traumatic injury (suggesting a kill rather than scavenging) can be washed away from the remains when submerged in water. Most crane mortality we attributed to Alligators, however, occurred in water that was deeper than that preferred (≤46 cm) for nocturnal roosting. When shallow marshes dry out, cranes must roost in deeper-water habitats such as livestock dugouts, canals, and lakes, where they are more vulnerable to Alligators that are concentrated there during dry periods. Alligators have been observed stalking prey on the water’s surface and while submerged (McIhenny 1935), and it could be difficult for cranes roosting in or near deep water to detect the approach of a submerged Alligator. Our finding of Whooping Crane remains in stomachs of Alligators is the first in the literature. We documented possible Alligator predation or scavenging on Whooping Cranes in 6 Florida counties, and there did not appear to be a regional concentration. Observations were from all months except February, August, September, and December. Crane use of shallow, seasonally flooded marshes during August and September may explain the lack of Alligator mortality during those months. Adult (≥1.8 m TL) Alligators rarely feed from mid-December through February. Therefore, the likelihood of predation during this winter period is lower. The significance of Alligator predation or scavenging may differ among populations of Whooping Cranes. The proportion of mortality of the Florida nonmigratory population (7.4%) associated with Alligators was greater than in that of the eastern migratory population (2.4%). This finding might be expected, based on the time each population spends within the range of the Alligator; for the nonmigratory population, it is year-round, whereas for the migratory population it is half the year or less. In addition, in recent years with relatively warm winters, many Whooping Cranes of the migratory population wintered north of the range of Alligators. Most (11 of 15) Whooping Cranes presumed taken by Alligators were ≤2 years of age. This finding may be due to the availability of young birds; most reintroduced Whooping Cranes were released when younger than 1 year, so the populations Southeastern Naturalist M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 74 Figure 4. Camera trap images of: (A) a pair of Florida Sandhill Cranes defending their nest against an Alligator (snout in circle) and (B) later tending their successfully hatched chicks. Southeastern Naturalist 75 M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 usually had a large proportion of relatively young birds. Additionally, released birds were raised in captivity, isolated from predators. Captive cranes lack the behavioral knowledge that wild birds gain from a long period (10–11 months; Lewis 1995) of parental care prior to independence. During this period, wild birds learn not only to avoid habitats inhabited by predators, but also how to react appropriately to threats from predators. We suspect that predation by Alligators is less prevalent in the only existing natural population of Whooping Cranes. The importance of Alligators as predators on that population is largely unknown, although it is unlikely that Alligators are actively feeding during most of the time that Whooping Cranes are wintering in Texas (the primary wintering area is in the same climatic zone as central Florida). Nonetheless, an Alligator has been observed in Texas with a Whooping Crane in its mouth (Stehn 2009). An intensive study using VHF radio transmitters would be required for determining causes of death in this population of cranes. Such work has been limited to a few years in the early 1980s, as part of a study focusing on migration (Kuyt 1992). Whooping Cranes wintering in Texas typically forage in water shallow enough (15–20 cm; F. Chavez-Ramirez, Gulf Coast Bird Observatory, Lake Jackson, TX, pers. comm.) that an approaching Alligator would be visible and perhaps audible. However, when water salinity requires the birds to travel to freshwater ponds to drink, they are more vulnerable to Alligator predation. Numerous Alligators are found in these freshwater ponds (T.V. Stehn, USFWS, Austwell, TX, pers. comm.). The one documented case in Texas of an Alligator with a Whooping Crane in its mouth was at a freshwater pond (Stehn 2009). There is an ongoing effort to reintroduce nonmigratory Whooping Cranes to Louisiana, another state with a thriving population of Alligators (Joanen et al. 1997). The Louisiana release site and vicinity contain more wetland acreage than do the release sites used in Florida, so biologists may expect Alligator predation to be a potential mortality factor. When cranes begin nesting in Louisiana, deployment of camera traps for monitoring the nesting success of that population may be useful in identifying predators. Alligators have not been observed preying on reintroduced Whooping Cranes of the Louisiana nonmigratory population, although the specific cause of death for 8 of 12 dead or missing (presumed dead) birds there could not be determined (S. Zimorski, Louisiana Department of Wildlife and Fisheries, Gueydan, LA, pers. comm.). Because this nonmigratory population shares wetland habitat with Alligators yearround, the likelihood of Alligator predation may be relatively high in Louisiana. Allen (1952) described historical habitat conditions in the range of Whooping Cranes in Louisiana as large areas with water depths 12–20 cm deep, which is perhaps why Alligators and Whooping Cranes could coexist in an environment with such a large Alligator population. Alligators large enough to prey on eggs, young, and adult Whooping Cranes may have been readily detected by cranes in such shallow water. Areas of marsh that are maintained today with water deeper than that described by Allen (1952) may allow more opportunities for Alligators to prey on Whooping Cranes. Southeastern Naturalist M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 76 Predation by American Alligators on Sandhill Crane nests has been documented in the literature at least twice. Butler (2009) documented predation on eggs of a Mississippi Sandhill Crane by an Alligator. Bennett and Bennett (1990a) reported that the nest of a Florida Sandhill Crane had failed because of an Alligator. We attributed failure of 2 Florida Sandhill Crane nests to predation on eggs by Alligators. In a previous study, several failed nests (no eggs or remains were found) of Sandhill Cranes were observed with Alligators on them; it was not known whether the Alligators had eaten the eggs or had just destroyed them as they crawled onto the nests (S.A. Nesbitt, Florida Fish and Wildlife Conservation Commission, Gainesville, FL, pers. comm.). Our documentation of the failure of a Whooping Crane nest as a possible result of Alligator egg predation is the first in the literature. Nests visited by Alligators were not unduly disturbed and would give no clue as to cause of nest failure were it not for the camera traps, surveillance video cameras, and artificial eggs employed in our study. Comparison of pictures of a Sandhill Crane nest before and after suspected Alligator predation shows little difference in structural integrity (Fig. 3). So, Alligator predation of crane eggs could go undetected in nesting studies. Cranes prefer to roost and nest in shallow marshes (M.J. Folk, pers. observ.), which would reduce the chance of encounters with larger Alligators. The shallower water of marshes also would make it easier for the cranes to detect an approaching Alligator. During drought, however, cranes in the southeastern United States are forced to nest on edges of lakes, borrow pits, and canals. These nests may be more vulnerable to Alligator predation and to disturbance from Lontra canadensis (Schreber) (River Otter) and humans. Nesting of Florida Sandhill Cranes on lakes had not been documented on any scale before 2002. During April, when marsh levels were relatively low, a helicopter survey of water birds on Lake Tohopekaliga in central Florida noted more than 200 Sandhill Crane nests in the emergent vegetation of the littoral zone (Kitchens et al. 2002). Such density of nests had never been documented and suggests that lake edges may provide significant nesting habitat for cranes in Florida. If increased temperature and evapotranspiration associated with climate change reduce the water levels of shallow marshes in Florida, cranes and Alligators may become more concentrated in the remaining nesting habitat. Future research should focus on determining the relative importance of lake edges for nesting Florida Sandhill Cranes. Conclusions All 4 populations of North America’s Whooping Cranes and 4 populations of Sandhill Cranes spend at least part of their year within the range of the American Alligator. Two populations of both crane species are nonmigratory and spend their entire life within the range of Alligators. We have documented evidence of Alligators taking adults and eggs of cranes. Even though Alligators are not the primary source of mortality for cranes, wildlife managers should be aware of their potential as predators, especially with regard to reintroductions of cranes. Cranes raised in captivity and released into the wild may be more susceptible to predation than those Southeastern Naturalist 77 M.J. Folk, A.R. Woodward, and M.G. Spalding 2014 Vol. 13, No. 1 raised by their parents in the wild. Water depths at release sites should be managed at optimal levels (10–20 cm) to discourage movement by larger Alligators and to allow greater visibility of Alligators that might approach the birds. Acknowledgments Thanks to W.B. Brooks, F. Chavez-Ramirez, D.L. Lopez, T.V. Stehn, and S.E. Zimorski for information on Whooping Crane populations. We thank S.B. Baynes, M.K. Chappell, and T.A. Dellinger for assistance with data collection. The manuscript benefited from reviews by B. Crowder, S.A. Nesbitt, J.A. Rodgers, and 2 anonymous reviewers. Major partners of the Florida Non-migratory Whooping Crane Project included the US Fish and Wildlife Service, US Geological Survey’s Patuxent Wildlife Research Center, Canadian Wildlife Service, International Crane Foundation, Windway Capital Corporation, Calgary Zoo, Lowry Park Zoo, Disney’s Animal Kingdom, San Antonio Zoo, and Audubon Zoo Species Survival Center. Funding for this work was supported in part by the US Fish and Wildlife Service via Cooperative Agreement No. 401814–J–035 and by the Florida Fish and Wildlife Conservation Commission. Literature Cited Ad Hoc Eastern Population Sandhill Crane Committee. 2010. Management plan for the Eastern population of Sandhill Cranes. 34 pp. Available online at http://media.timesfreepress. com/docs/2010/09/Sandhill_EP_plan_FINALFeb2010.pdf. Last accessed February 2014. Allen, R.P. 1952. The Whooping Crane. National Audubon Society Research Report 3. National Audubon Society, New York, NY. 246 pp. Audubon, J.J. 1838. The Birds of America. 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