2012 SOUTHEASTERN NATURALIST 11(2):205–218 Effects of Feral Swine (Sus scrofa) on Alligator (Alligator mississippiensis) Nests in Louisiana Ruth M. Elsey1,*, Edmond C. Mouton, Jr.2, and Noel Kinler2 Abstract - Rapid spread of the introduced Sus scrofa (Feral Hog) is a major concern for many landowners and land managers due to its destructive rooting behavior which damages natural habitats. Feral Swine have also been reported as infrequent predators of Alligator mississippiensis (American Alligator) eggs, with only seven nests lost in three prior studies combined (Fogarty 1974, Ruckel and Steele 1984, Woodward et al. 1992). In response to increasing reports by Louisiana landowners of Alligator nest losses due to Feral Swine, we sent a questionnaire addressing this issue to licensed Louisiana Alligator farmers who are permitted to collect eggs from wild nests. Over half (51.4%) of the farmers reported loss of Alligator nests in 2011; some 590 nests were damaged or destroyed on 36 separate properties across the state. Four farmers, some of whom have twenty or more years of experience collecting Alligator eggs, reported this is the first year in which they have lost nests to Feral Swine. Other farmers reported seeing wild hogs while in the field or seeing sign of hogs, which suggests future potential losses may be incurred and that the range and population level of this non-native species is expanding in important Alligator nesting habitat in Louisiana. Nearly all farmers who had nests destroyed by Feral Swine (94.7%) reported hog damage is increasing on their properties. Some farmers reported that hog removal efforts limited their Feral Swine damage this year relative to past years. In addition to deleterious effects on wetlands habitats caused by Feral Swine, the financial impact of loss of the Alligator egg revenue is significant. Introduction Many landowners across the United States are experiencing problems with property damage from Sus scrofa L. (Feral Swine), which are expanding their range (Ditchkoff and Mayer 2009, Mayer and Brisbin 2009). In addition to agricultural and residential damage, Feral Hogs can destroy crops, damage wildlife habitat, compete with other species for food, prey on wildlife, and transmit diseases to wildlife, livestock, and humans (Kimmel 2011, Perot 2011). They have established populations in at least 38 states and are spreading rapidly, with estimated economic losses to agriculture and the environment at $800 million annually (Mouton 2009). Additionally, their extensive rooting of soils can disrupt wetlands and lead to wetlands losses in already fragile ecosystems (Mouton 2009). Methods are being developed to accurately survey wild pigs (Williams et al. 2011), and recent legislation has been enacted in Louisiana to provide more options for property owners to take outlaw quadrupeds, including 1Louisiana Department of Wildlife and Fisheries, 5476 Grand Chenier Highway, Grand Chenier, LA 70643. 2Louisiana Department of Wildlife and Fisheries, 2415 Darnall Road, New Iberia, LA 70560. *Corresponding author - relsey@wlf.la.gov. 206 Southeastern Naturalist Vol. 11, No. 2 Feral Hogs (Louisiana Department of Wildlife and Fisheries press release, 14 July 14 2011; Perot 2011). Studies are underway in Louisiana to evaluate the possible effect of soil quality on reproductive efficiency in this prolific species (O’Boyle and Tolson 2011) that may help elucidate why their range is expanding in certain regions, and a recent report (Mayer and Brisbin 2009) reviews management and control techniques for this damaging species. Although Feral Hogs have only rarely been noted as a predator of Alligator mississippiensis Daudin (American Alligator; hereafter just Alligator) eggs in Louisiana (McIlhenny 1935), their recent population growth and range expansion could make this mortality factor of greater import adversely affecting Louisiana’s valuable Alligator population. Numerous studies have been conducted on the nesting ecology of Alligators in southeastern states, and wildlife managers in Louisiana, Florida, South Carolina, Texas, and Georgia have documented nest losses due to flooding and predation (Cooper and Slaughter 2008, Deitz and Hines 1980, Fleming et al. 1976, Goodwin and Marion 1978, Hunt and Ogden 1991, Joanen 1969, Metzen 1977, Platt et al. 1995, Ruckel and Steele 1984, Wilkinson 1983). Procyon lotor L. (Raccoons) are the most often cited mammalian predator in these studies, but in some cases Lontra canadensis Schreber (River Otters) have been suspected as predators on Alligator eggs (Deitz and Hines 1980), and Ursus americanus Pallas (American Black Bears) have also been documented as causing nest/egg loss (Hunt and Ogden 1991, Metzen 1977). In McIlhenny’s (1935) classic study on Alligators, he noted Alligator eggs to be eaten by a number of animals, including “’coons, opossums, skunks, hogs, and bears”. Fogarty (1974) noted a hog was seen rooting through one of 64 nests (1.6%) studied in the Florida Everglades. More recently, Ruckel and Steele (1984) noted that four of 31 nests at their Rhetts Island study site in Georgia were destroyed by Feral Hogs, and one other nest was destroyed by a combination of Raccoons and Feral Hogs; thus, 5 of 31 nests (16.1%) were lost all or in part to Feral Hogs. In a long-term, multi-year study in Florida, Woodward et al. (1992) noted one nest was depredated by Feral Hogs, as evidenced by extensive rooting and hoof-prints around the nest. Biological staff from our agency noted signs of hog presence in nesting areas and nests destroyed by hogs in 1997 during a pilot study evaluating Alligator nests in swamp habitat with a cooperating eggcollection permittee (Campbell 1997). Commercial Alligator farming programs exist in many southeastern states, including Louisiana. A major component of the program in Louisiana involves egg “ranching”, wherein Alligator farmers may collect eggs from nests in the wild to stock Alligator farms under permits and quotas established by the Louisiana Department of Wildlife and Fisheries (LDWF). This program has been described in detail (Elsey et al. 2001), and can have an economic value of nearly $60 million in strong market years for the valuable leather industry (LDWF 2009). To better evaluate Alligator nest losses and quantify potential impact to Alligator nesting habitat in Louisiana due to Feral Hogs, we developed a brief 2012 Ruth M. Elsey, Edmond C. Mouton, Jr., and Noel Kinler 207 questionnaire to request information on nest destruction due to this species. Information obtained might be of use in assisting wildlife managers in controlling Feral Hogs on their properties which may damage valuable wetland resources, including Alligator eggs. Methods A brief (one page) questionnaire was developed and sent to licensed Alligatoregg permittees (licensed Louisiana Alligator farmers, who have permits to collect Alligator eggs from the wild). Thirty-seven farmers have such egg permits and were mailed the questionnaire. Self-addressed stamped return envelopes were provided to facilitate replies to the brief survey, and a cover letter assured respondents their replies would in no way affect future egg quotas which are determined by our agency. One Alligator farmer/permittee was coincidentally in the LDWF office on the day the questionnaire was to be mailed; he was provided his copy in person. Another Alligator farmer had provided some information on Feral Hog damage when an informal inquiry was sent to him via e-mail; he was not mailed another form, and details were obtained in follow up e-mail correspondence and by telephone. The form also indicated farmers could telephone the LDWF office and discuss their answers and observations over the telephone, rather than having to complete the written questionnaire, if this was easier. The brief questions included: 1. Did you see any evidence of hog (Feral Pig) damage to Alligator nests during your collections this year? 2. If so, on which land companies did you see hog damage to Alligator nests? (please list how many nests damaged on each property; and whether they were slightly damaged or completely destroyed). Please provide as much detail as is possible. Any photos are appreciated as well. 3. Have you ever seen hog damage to Alligator nests in past years? List years if possible. 4. Does hog damage seem to be increasing on your properties, decreasing, or staying about the same? 5. Have you observed live hogs in the marsh when collecting eggs or flying to mark nests? If so, which properties? 6. Have you seen hog sign (footprints/tracks, scats/droppings, etc.) near nests while collecting nests? 7. How many years have you been collecting eggs from the wild? The questionnaire was mailed in mid-July (July 19), by which time a few farmers may have already recently completed the summer’s egg collections, but many would still be actively collecting eggs. Thus, we hoped most farmers would remember if they had seen any evidence of Feral Swine damage, but we did not want to seem to be “encouraging” reporting of questionable findings or cause over interpretation of damage to Alligator nests caused by other means. The number of licensed egg permittees is low (n = 37), and we had a 100% response rate. In some cases, this was done via telephone and we recorded the information supplied. 208 Southeastern Naturalist Vol. 11, No. 2 We were confident Alligator farmers could distinguish nest depredation by Feral Swine from other predators (mainly Raccoons), as nests depredated by Raccoons typically have numerous small penetration holes, apparently made Figure 1. An Alligator nest depredated by Raccoons. The nest damaged by Raccoons is mostly structurally intact, with eggshells scattered about the exterior of the nest. Figure 2. A typical undamaged Alligator nest. The typical nest has eggs concealed within the inner egg cavity. 2012 Ruth M. Elsey, Edmond C. Mouton, Jr., and Noel Kinler 209 as Raccoons probed for eggs (Figs. 1, 2; Woodward et al. 1992). Feral Hogs would generally create more nest damage and disrupt the integrity of the nest mound with rooting activities, and hoof prints and tracks of pigs might be seen at the nest site (Fig. 3). Additionally, nearly 68% of licensed Louisiana Alligator farmers have over twenty years of experience collecting Alligator eggs and thus were felt to be reliable observers in submitting the requested data. Figure 3. Photo showing an Alligator nest damaged by Feral Swine. Note the extensive damage and disruption of nest integrity caused by Feral Swine. Photograph © Jeff Donald. 210 Southeastern Naturalist Vol. 11, No. 2 The survey was not developed until after the egg collection season started; thus, the results in this study are in many cases estimates the farmers made after completing egg collections. If a farmer reported a range of nests damaged (for example, “3–4 nests lost on Property A”), we would assume the lesser quantity and consider three nests lost. If they reported a range such as “8–10 nests lost on Property B”, we considered this as nine nests lost. The farmer with the most nests damaged reported an estimate based on a percentage of nests damaged in each section that the ultra-light aircraft pilot surveyed, and the number of nests ultimately marked (the pilot did not throw a nest marker at nests already destroyed by Feral Swine at the time of survey, as ground crews would not need to visit that individual nest site). Some farmers specifically reported they did not have hog damage but did lose a few nests to Raccoons; others reported some Feral Swine damage but more Raccoon damage, which lent support to our supposition that Alligator farmers could distinguish the two factors. One farmer reported rare Alligator nest losses due to bears; the property manager has frequently observed bears on the area but has not observed hogs. Hundreds of Alligator egg permits are issued to licensed Louisiana Alligator farmers annually; in 2011, 531 permits were issued to individual properties with a total egg quota total of over 785,000 eggs. The number of egg permits individual farmers have varies widely (range = 1–75); the number of eggs in each farmer’s quota total ranges from 700 eggs to 95,915 eggs. The single smallest permit has an egg quota of 35 eggs, and the largest single permit has a quota of 55,535 eggs. Alligators occur statewide in Louisiana, but the majority of the Alligator habitat (and thus Alligator nests, population, and egg quotas) occur in the coastal parishes. A variety of habitats exist, including large lakes, upland areas, cypress tupelo swamps, and coastal marshes (Elsey and Kinler 2004). Results Alligator nest damage in 2011, extent of nest damage, and properties affected Numerous farmers (51.4%) reported Feral Swine damage to Alligator nests in 2011. Nineteen farmers reported losing approximately 590 Alligator nests to Feral Swine in 2011. Properties affected were broadly distributed across the state (Fig. 4), although more occurred in the coastal zone where Alligator populations are greatest. Two farmers who collect eggs on one large property lost some 315 nests as a conservative estimate for their combined collections. They successfully collected 40,500 eggs combined; but lost approximately 25% of the nests produced to Feral Hogs. One farmer with 75 egg permits lost 132 nests on nine properties; fifty nests were lost on his largest property, which had about one third of his entire egg quota. One farmer lost 27 nests on a single large wetland property; another farmer with a single egg permit lost 10 of 39 (25.6%) Alligator nests he located to hog damage. In 2011, Louisiana Alligator farmers collected over 352,000 eggs from some 13,000 nests. Thus, the estimated 600 nests damaged by hogs represents approximately 4–5% of the nests collected. 2012 Ruth M. Elsey, Edmond C. Mouton, Jr., and Noel Kinler 211 Some farmers reported damage on only one property; others noted hog damage to multiple properties. Nest quantities reported damaged ranged from one to approximately 300. Most farmers reported damaged nests were totally destroyed; one farmer verbally reported the nests were “flattened”. Only one farmer noted that in some cases they were able to collect some eggs from nests partially damaged by Feral Swine. Another farmer reported the top of the nest was torn away and a few eggs consumed; the other eggs were scattered and lost due to heat exposure. The damaged or destroyed nests were located on 36 separate properties across the state (Fig. 4). One farmer noted hog damage to nests on seven different properties in 2011 (approximately 15 nests lost). His most severely affected property might have been damaged even more extensively had it not been for the trapping and removal of 69 Feral Swine this year. Another farmer removed over 50 pigs by trapping; he has seen hogs and hog sign near nests for many years, but this is the first year he actually lost two nests to rooting by hogs. Figure 4. Map showing parish locations with hog damage in Louisiana in 2011. Each point represents a property with at least one nest damaged by Feral Swine and indicates the parish wherein that property is located. Points located on the border of two parishes represent land properties with hog damage with sufficient acreage that the properties are located within two adjoining parishes. 212 Southeastern Naturalist Vol. 11, No. 2 Prior Alligator nest damage and trends in Alligator nest damage Most farmers who saw damage in 2011 had seen damage previously over the last few years. One farmer in southwest Louisiana had a decreased nesting effort in 2011 due to severe drought; thus, he did not attempt egg collections and could not asses hog damage, but he had previously seen hog damage to Alligator nests on several properties. Another farmer similarly affected by drought saw so few nests he did not collect eggs in 2011 in southwest Louisiana, but he previously had seen Feral Swine damage in southeast Louisiana. Four farmers noted nest damage attributed to Feral Swine in 2011, but had not seen this previously in the 15 to 22 years experience each had collecting Alligator eggs, indicating Feral Hogs may be just now extending their ranges in coastal Louisiana and/or increasing the overall population level. Nearly all farmers (94.7%) who reported Feral Swine damage in 2011 noted that hog damage was increasing based on their observations. Several farmers noted they would previously observe rare hog damage in isolated locations affecting one or two nests, but now see “areas” with larger regional damage of several nests. Another farmer similarly described “hot spots” of extensive hog damage, and said Feral Swine damage seems to be worse in each successive year over the last three or four years. One farmer noted that they were seeing less hog damage due to their eradication program, but the overall range of hogs on their property had increased. This farmer/land manager had extensive records, and noted a yearly increase in hog damage, beginning with approximately ten nests lost to Feral Swine in 1998 to approximately 100 nests lost in 2008. Due to their hog eradication program, they lost fewer nests (n = 27) in 2011 to hog damage. Thus, three farmers (two others as noted above in “extent of nest damage”) described beneficial effects of hog eradication programs in limiting swine damage to Alligator eggs/nests. Three farmers who did not lose Alligator nests to Feral Swine in 2011 did report that they saw an increase in hog damage to their properties. One farmer verbally reported a “population explosion” of Feral Swine causing problems to him as well as local corn farmers. One farmer said hog damage was decreasing, but this is based on having had one nest destroyed three years ago and none since. Observations of live Feral Swine and hog sign Most farmers who saw egg damage to nests reported having seen live hogs both while collecting eggs or when flying to mark nests for later collection by airboat. One farmer spontaneously remarked he saw Feral Swine “by the dozens” while conducting egg-collecting activities. Several farmers noted their pilots (helicopter or ultra-light aircraft) observed live hogs or nest damage while surveying to locate nest sites; some saw nests already destroyed and thus did not mark those nests for later collection. Five farmers who had not yet experienced nest loss/ damage to hogs (or had no damage this year, but did in the past) saw live hogs on their properties while collecting eggs or marking nests. 2012 Ruth M. Elsey, Edmond C. Mouton, Jr., and Noel Kinler 213 As expected, farmers who incurred nest losses to Feral Swine reported seeing hog sign at nests. Of additional concern is that four farmers reported seeing hog sign (tracks, rooting) on their properties (but no damage to nests as of yet), indicating they may have the potential to suffer nest losses as well as continued wetlands disruption or erosion in future years. Experience level of respondents Most farmers who are currently active have been licensed Alligator farmers for many years; many since the inception of the Alligator egg “ranching” program in 1986. Twenty-three of 34 (67.65%) farmers who responded to this question had over twenty years of experience and observations. Only four respondents had less than ten years experience collecting eggs, with the least experienced surveyed farmer having four years of egg-collecting experience. Thus, in total, the farmers surveyed have an extensive experience level and have observed a past lack of Feral Swine and/or seen the influx of this species over the years. Discussion The very high numbers of total nests now being lost and large proportion of Alligator farmers losing valuable Alligator nests and eggs to Feral Hogs was an unanticipated result and cause for some concern. A disturbing trend was also noted of most farmers reporting increasing evidence of hog presence and damage to their wetlands, Alligator habitat, and egg resources. Several experienced Alligator farmers saw hog damage for the first time in 2011, suggesting populations of this non-native species are rising and/or expanding their range in Louisiana. The results presented here are minimums. Some pilots did not mark nests that they saw from the air were already destroyed; thus, ground crews would not have encountered these nests and they would have been unreported as having been damaged by hogs. Also, some remaining uncollected nests (if any were left after a farmer collected his full egg quota on a property) may have been later depredated by Feral Swine. Early egg collection of Alligator nests can prevent flooding, predation, and lightning fire losses; avoiding high natural mortality was a factor considered in implementing egg-collecting programs in Louisiana (Elsey and Trosclair 2008). Avoidance of Feral Hog damage could also be a reason to encourage participation in egg-collecting programs in some regions. One farmer suggested his early egg collections (late June) averted hog losses seen the prior year when he had collected later than usual (mid-July). Farmers who have “hot spots” with extensive hog presence should perhaps be encouraged to collect these areas first to avoid nest losses. It may well be that Feral Swine damage to wild Alligator nests may have been far greater if the egg-collecting program were not in place, which limits some of the natural mortality factors. It may also be that unusually high water levels in 2011 (Mississippi River levels were much higher than normal due to record snowfall in northern states) led to increased hog damage this year. In contrast, however, Fleming et al. (1976) 214 Southeastern Naturalist Vol. 11, No. 2 reported an absence of predation by Raccoons on Alligator nests after prolonged high marsh water levels. Mazzotti (1989) attributed low levels of Crocodylus acutus Cuvier (American Crocodile) nest predation to the low density of active nests in any given year. It may be that the higher than average Alligator nesting in southeast Louisiana in 2011 led to the observed increase in Feral Swine damage seen this year, in addition to what clearly appears to be range and population expansion of Feral Swine statewide. Six farmers noted damage on other properties in past years that were not damaged this year; it would be of interest to determine why some properties are targeted or if Feral Swine move vast distances regularly and thus affect Alligator nests randomly in various locations. Nest losses have also occurred in other crocodilian species due to pigs; Webb et al. (1983) noted Feral Hogs took five nests at one site (6% of the total) in a study on Crocodylus johnstoni Krefft (Australian Freshwater Crocodile) nesting. Similarly, Hall and Johnson (1987) documented losses of nests of Crocodylus novaeguineae Schmidt (New Guinea Crocodile) due to predation by Varanus sp. Merrem (varanid lizards) and Feral Hogs. Platt et al. (2008) noted a nest of Crocodylus moreletii Dumeril, Bibron, and Dumeril (Morelet’s Crocodile) was destroyed by Tayassu tajacu L. (Collared Peccary) in northern Belize. Crawshaw and Schaller (1979) suggested possible local vertebrate predators in their study of Caiman crocodilus yacare Daudin (Yacare Caiman) in Brazil were Sus scrofa domesticus L. (Domestic Pigs) and Tayassu (peccaries), among others. Campos (1993) also documented tracks and feces of Feral Hogs near nests of Yacare Caiman that had been destroyed by predators in the Pantanal of Brazil. Larriera and Pina (2000) also found Feral Hog destruction of Caiman latirostris Daudin (Broad-nosed Caiman) nests in northern Argentina. The apparent recent increase in Alligator nest losses due to Feral Swine is a disturbing trend that should be continued to monitored closely, but we do not believe this is an imminent threat to Alligator populations. However, this additional mortality factor could become problematic if it continues to increase unchecked; and we anticipate continued collection of hog-damage data in future years. In recent years, our aerial nesting surveys have estimated over 30,000 nests just in coastal Louisiana; thus, the nearly 600 nests lost to Feral Swine would represent some 2% of the statewide nest production. The possible financial losses due to Alligator egg destruction by pigs to Alligator industry personnel could be significant. If eggs are valued at $10 each and using conservative estimates of 25 eggs per nest, a loss of $147,500 would be incurred for just the egg value; there would be an additional loss of revenue from the finished leather-goods products. Although this study is limited in scope to Alligator nest damage, of greater concern is the negative impact these invasive Feral Swine are having by damaging wetlands along the coast of Louisiana that are recovering from damage by Myocastor coypus Molina (Nutria) (Mouton 2009). Indeed, researchers have determined that Feral Swine damage to coastal wetlands is more severe than Nutria damage (Mouton 2009). 2012 Ruth M. Elsey, Edmond C. Mouton, Jr., and Noel Kinler 215 Many mammalian predators prey upon Louisiana’s resident Anas fulvigula Ridgway (Mottled Duck), affecting nesting females, ducklings, adults during remigial molt, and eggs (Moorman and Gray 1994). Feral Hogs have the potential to prey upon this species, which is of concern due to uncertain population status, and hunter bag limits have recently been decreased from three Mottled Ducks per day to one in Louisiana. Feral Hogs have also been reported to destroy Meleagris gallopavo L. (Wild Turkey) nests (Perot 2011), another popular game species in Louisiana. Other concerns noted by two Alligator farmers were Feral Swine damage to local corn farmers, one egg collector reported sugar cane farmers are also seeing adverse effects due to Feral Swine damage. As far back as 1929 (Kellogg 1929), the range of swine and Alligators have apparently overlapped in Louisiana, as a hog was reported found in an Alligator stomach on Rainey Wildlife Refuge in Vermilion Parish. McIlhenny (1935) also describes witnessing Alligators taking hogs and details one instance of a “duroc boar hog” weighing not less than 500 pounds being taken by a large Alligator while the hog was swimming across a stream. O’Neil (1949) noted hogs as a predator of Ondatra zibethicus L. (Muskrats) in Louisiana coastal marshes. However, Alligators preying on hogs is relatively uncommon; Neill (1971) said “troops of Feral Hogs, so common in parts of the Southeast, are not often menaced by Alligators.” Taylor (1986) noted hogs in two of 111 Alligator stomachs (1.8%) examined. In Georgia, Shoop and Ruckdeschel (1990) noted Feral Swine in five of 28 Alligator fecal samples from scattered localities on Cumberland Island. Although the finding of Alligator nest losses is not new, and the range of Alligators and swine in Louisiana is known to overlap, the recent tremendous increase in extent of damage, apparent Feral Hog range expansion, and potential for future continued losses are of concern. Land managers and industry participants may work together with regulatory agencies to consider eradication programs in the future. Those farmers and land managers who saw live hogs or signs of hog damage to wetlands (despite them not yet having experienced actual Alligator nest losses) might be encouraged to consider eradication in the future to avoid later costly loss of Alligator nests and to collect nests in those areas as early as possible to avoid Feral Swine damage. The role of the female Alligator in nest defense as a deterrent to hog depredation could be an area for future investigation. The Feral Swine may be another example of a non-native introduced species which has led to serious unanticipated consequences. It was encouraging to receive reports that several proactive farmers or land managers who trapped or removed hogs believed it did limit even further Alligator nest damage than was reported. Future research might help elucidate if there is a habitat type preferred by hogs where the most nest damage occurs or if they are generalists and adapt to many habitat types. 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