long-distance movement by american alligators in southwest ... · 2011 southeastern naturalist...

SOUTHEASTERN NATURALIST2011 10(3):389–398

Long-distance Movement by American Alligators in Southwest Louisiana

Valentine A. Lance1,*, Ruth M. Elsey2, Phillip L. Trosclair III2, and Leisa A. Nunez2

Abstract - As part of an ongoing study on growth and sexual maturation of Alligator mississippiensis (American Alligator) on Rockefeller Wildlife Refuge, LA, 3601 speci-mens, ranging in total length from 28 to 361 cm, were captured from June 2000 through August 2004. Additionally, 70 alligators were collected opportunistically as part of a teaching exercise in August 2005, and 248 more were collected in 2006 (and one in January 2007) as part of a study evaluating the effects of Hurricane Rita on alligators. Representative samples from size classes greater than 60 cm were collected in most months of the year between 2000 and 2004. Each animal was tagged, measured, sexed, and released immediately at the site of capture. A large number of these marked alli-gators were recaptured outside the refuge boundaries during annual alligator hunts in September. Of the 286 recaptured alligators, 214 were males, 68 were females, and four were of undetermined sex. From each recaptured alligator, total body length and date of recapture were recorded, and minimum distance from initial capture site estimated. From these preliminary data, we calculated the time interval between captures, and plotted minimum distance moved. The number of days between first capture and recap-ture ranged from 29 to 3336 days (9.1 years). Distance moved from initial capture site to final capture site ranged from 0.3 to 90.2 km. Eleven alligators moved between 30.0 and 39.9 km, and eight moved ≥40 km. Six of these moved between 40.0 and 49.9 km, and the others moved 87.4 and 90.2 km. These results greatly extend previous estimates of long-distance movement by alligators and demonstrate that both sub-adult and sexu-ally mature animals move considerable distances. These data also showed that smaller alligators moved greater distances than larger alligators (P = 0.0002), and that the lon-ger the time between captures, the greater the distance moved (P < 0.0001).

Introduction

Home range and dispersal (total distance moved) have been studied in a number of Alligator mississippiensis Daudin (American Alligator) populations using capture-recapture of marked animals or radiotelemetry. One of the earliest studies (Chabreck 1965) involved a total of 2024 alligators marked over a seven-year period on Rockefeller Wildlife Refuge (RWR) and Sabine National Wildlife Refuge in coastal southwest Louisiana. Of these marked alligators, 131 were recaptured; of these, eighteen were recaptured twice, and two were recaptured three times. The conclusions of the study were that immature alligators moved greater distances than adults, and that the longer the interval between fi rst and second capture the greater the distance moved. The longest movement recorded was approximately 16 km for an animal recaptured after four years. This study

1Graduate School of Public Health, San Diego State University, San Diego, CA 92128. 2Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA 70643. *Corresponding author - [email protected].

Southeastern Naturalist Vol. 10, No. 3390

was limited to recapture attempts made within the refuge boundaries, and it is likely that any alligators that had moved greater distances to surrounding private lands would not have been recaptured. In the Florida Everglades, Hines et al. (1968) marked approximately 1000 alligators and recaptured 33. The longest reported distance moved was 11 km for an alligator recaptured after 850 days. Joanen and McNease (1970) were the fi rst to use radio-telemetry to study the movement of alligators on Rockefeller Refuge. Five adult females were fi tted with radio-collars and monitored for a period of six months. The results showed that nesting females did not move far from the nesting/den site, with home ranges of 2.6 to 16.5 ha. Taylor (1984) fi tted radio-collars on nine adult female alligators in a lake habitat in north Louisiana and reported home ranges of 0.6 to 256 ha. A study by Rootes and Chabreck (1993a), in which fi fteen adult female alligators (in southwest Louisiana) were fi tted with radio-collars and followed for one year, indicated home ranges of 6.1 to 165 ha. In none of these studies on female alliga-tors was the longest distance from initial site of capture reported. On the other hand, 14 adult male alligators on Rockefeller Refuge fi tted with radio-collars and followed for up to one year, moved considerable distances and had estimated home ranges of 183 to 5083 ha (Joanen and McNease 1972). The greatest dis-tance an adult male alligator moved from the initial capture site to where it was observed 146 days later was approximately 53 km; another adult male moved 22 km (Joanen and McNease 1972). Elsey (2005) reported an adult alligator photo-graphed in the Gulf of Mexico some 63 km from the nearest land. Studies on juvenile alligators fi tted with radio-collars (McNease and Joanen 1974, Taylor et al. 1976) reported no differences in home range between male and female alligators, but found that juveniles exhibited greater daily activity than adults and moved greater distances overall. Rootes (1989) suggested that radio-telemetry units attached as “collars” placed over the neck of alligators are likely stressors that could greatly limit mobility. Thus, distances moved by alliga-tors monitored with telemetry units might be biased toward lower distances due to restricted movement. Similar observations on juvenile alligator activity (i.e., that they generally moved greater distances than adults) were made by Chabreck (1965) and Hines et al. (1968) using mark-recapture rather than telemetry. In this paper, we present data on long-distance movements of alligators based on a large sample of juveniles and adults of both sexes captured and recaptured over a period of nine years in southwestern Louisiana.

Materials and Methods

Rockefeller Wildlife Refuge (RWR) is a coastal marsh in southwestern Loui-siana encompassing some 29,380 ha (Fig. 1) of wetlands of varying salinities (fresh: <2 ppt, intermediate: 2 to 6 ppt, brackish: 6 to15 ppt, and saline: >15 ppt; Keddy et al. 2007). As part of an ongoing study on growth and sexual maturation of American Alligators (immature: 50 to 180 cm; adult: >180 cm TL) on RWR, 3920 specimens (1960 males, 1926 females, 34 of unknown sex) ranging in total length (TL) from 28 to 361 cm were captured from June 2000 through January 2007; however, the majority of captures (3601) were made by August 2004. Representative samples from size classes ≥ 60 cm were taken in most months.

V.A. Lance, R.M. Elsey, P.L. Trosclair III, and L.A. Nunez2011 391

Small alligators were caught by hand from an airboat, and larger animals were captured using a cable noose snare attached to a long pole (see Lance et al. 2009 for details). Each animal was marked with a monel tag in the webbing of both rear feet (Elsey et al. 2000), TL was measured, a blood sample was collected from the spinal vein (Zippel et al. 2003), a dorsal scute was removed from the tail, and sex was determined before being immediately released near the site of capture. During the annual fall alligator harvest, Louisiana Department of Wildlife and Fisheries (LDWF) employees were stationed at checkpoints where harvested al-ligators were brought for processing. Recaptures were identifi ed by presence of tail notches and web tags; these specimens were measured, and distance from site of original capture was calculated by plotting the minimum distance between the property where the alligator was captured to the capture site on RWR. Alliga-tor trappers are issued harvest tags to be used on specifi c wetlands they own or lease, thus enabling determination of the approximate capture area. Additional data were provided on mail-in forms for reporting the take of a marked alligator, which were supplied to all licensed trappers prior to the harvest season. Data were analyzed using SAS® statistical software. First, multiple regres-sions were used to determine if there was a linear relationship between total distance moved and either initial body size or number of days between release and recapture. Multiple rather than simple regression was used because the data collected on a single alligator are not independent from one another. Data were

Figure 1. Satellite map of coastal southwest Louisiana showing Rockefeller Wildlife Ref-uge (outlined) and locations of alligators that moved the greatest distance from site of fi rst capture (white-fi lled circles). The Gulf of Mexico is due south of the Refuge.


separated by sex, as plots of the raw data suggested an obvious difference be-tween males and females. These regressions were performed without an intercept, as the distance moved should be zero when either initial body size or number of days is zero. The model for each sex was: Distance = 1 (Days) + β2 (Length) + ε, where ε represents the random variation for each subject. Both models violated the assumption of normality of residuals (P-values for both sexes were <0.0001), and also showed evidence of violating the assumption of homogeneity of vari-ance. Consequently, the Spearman rank correlation coeffi cient was calculated to determine the nature of the relationship between total distance moved and either initial size or number of days between release and recapture. This statistic does not require the relationships to be linear, and the distribution need not be either normal or defi ned. The values of this coeffi cient fall between -1 and 1, with nega-tive values indicating a decreasing relationship, and positive values indicating an increasing relationship. The P-values correspond to the hypothesis that the coeffi cient is zero (no relationship). Alligators recaptured on Rockefeller Refuge were not included in the analysis.

Results

A total of 286 alligators were recaptured outside of RWR, including 214 males, 68 females, and four of unknown sex. Eleven alligators moved between 30.0 and 39.9 km, and eight moved more than 40 km. Six of these moved between 40.0 and 49.9 km, and the other two moved 87.4 km, and 90.2 km (Table 1). Al-though more than half of the alligators (155) moved <10 km from point of fi rst capture, there was a signifi cant positive relationship between number of days since capture and distance moved (Fig. 2). There was also a signifi cant negative rela-tionship between size at initial capture and distance moved; i.e., smaller alligators moved greater distances than larger alligators (Fig. 3). Although the correlation coeffi cients for each of these relationships are low, the results were highly signifi -cant (Spearman Rank Correlation [n = 281] for distance moved and number of days since fi rst capture, ρ = 0.26652, P < 0.0001; distance moved and length at fi rst cap-ture, ρ = -0.22354, P = 0.0002) when a non-parametric analysis is conducted. Thus, smaller alligators tended to move greater distances, and distances moved were greater with increasing time since fi rst capture.

Table 1. Distances moved by American Alligators marked on Rockefeller Wildlife Refuge, LA and later recaptured outside of the refuge boundaries. Of the 286 total, only data for those that moved ≥10 km are shown.

Distance moved (km) Number of alligators

10.0–19.9 73 20.0–29.9 39 30.0–39.9 11 40.0–49.9 6 50.0–59.9 0 60.0–69.9 0 70.0–79.9 0 80.0–89.9 1 90.0–99.9 1


The multiple regression analysis for females had an r2 value of 0.8273 (F2,65 = 161.5, P < 0.0001), and for males had an r2 = 0.5544 (F2,212 = 134.15, P < 0.0001). Larger females tended to move greater distances than smaller females (regression parameter = 0.11808, P < 0.0001); this relationship was not evident in males; i.e., smaller males tended to move greater distances. Greater distances were moved over longer time periods (number of days) for both sexes, with regression

Figure 2. Plot of days between fi rst and fi nal capture and distance moved of American Alli-gators (n = 286) captured outside of the boundaries of Rockefeller Wildlife Refuge, LA.

Figure 3. Plot of distance moved and total length at fi rst capture for American Alligators (n = 286) captured outside of the boundaries of Rockefeller Wildlife Refuge, LA.


parameters of 0.00664 (r2 = 0.8325, P = 0.0035) for females and 0.00302 (r2 = 0.5586, P < 0.0001) for males. In addition to obtaining recapture data from the recovery of marked alligators outside RWR during annual hunts, 551 of previously marked alligators were cap-tured alive during mark-recapture efforts on RWR. Of these, 423 were recaptured once, 54 were recaptured twice, and six individuals were recaptured three times. As these were all caught within the refuge boundaries, we did not expect many to have traveled a great distance (minimum distance between eastern and western boundaries of sampling sites = 22.9 km). However, seven alligators moved over 10 km (range = 12.5 to 21.3 km) within RWR, and 154 (27.9%) moved from the impoundment in which they were initially caught to adjacent areas, although distances were <10 km. Most live recaptures (390 of 551, 70.8%) within RWR re-mained within the same impoundment in which they were originally caught. This result was not unexpected as live recapture efforts were limited to the original area wherein the alligators were marked. Most of these impoundments are rectan-gular in shape, 2 to 3 km in length and width, and encompassing areas of 600 to 800 ha; thus alligators could move substantial distances, but still remain within a single impoundment. Additionally, 208 marked alligators were recaptured in the nuisance harvest on RWR. As expected, most did not move long distances, and recoveries were all within the boundaries of RWR. However, fi ve of the nuisance alligators moved >10 km from the initial capture site (range of minimum disper-sal distance = 10.7 to 16.3 km), and two others moved a minimum of 9.1 and 9.3 km from the initial capture site to the harvest site.

Discussion

The results of this study document unusually long distance movements by ju-venile and adult alligators over a nine-year period. In this study, we were able to collect data unavailable to previous researchers, and thus greatly increase both recovery of marked individuals and confi rmation of distances moved. One of the unplanned benefi ts of a well-regulated hunting program is the ability to col-lect biological data from captured alligators; thus, with a small number of trained biologists and technicians, we were able to monitor numerous sites for marked animals captured during the hunt. Hence, we were able to collect data that previous studies, carried out before legal hunting was established, were unable to do. For ex-ample, Chabreck (1965) marked 2024 alligators, but only recaptured 131 (6.4%). Likewise, Hines et al. (1968) marked approximately 1000 alligators and recaptured only 33 (3.3%). In contrast, we marked 3920 alligators on RWR and obtained data on 286 (7.3%) recaptured on lands outside of the refuge, a considerably greater number than recovered in previous studies, in part because of the long duration of our study. Long-term studies obviously have a higher likelihood of detecting long-range dispersal over time. For example, Campos et al. (2006) studied a population of Caiman crocodilus yacare Daudin (Caiman) in the Brazilian Pantanal over a 16-year period and recovered 532 of 7618 marked individuals (6.9%). We previously reported a male bias (58%) among sub-adult alligators in Loui-siana (Lance et al. 2000). In the present study, 216 of 283 (76%) alligators were males, a higher percentage than previously reported for this population (Lance et


al. 2000). As these alligators were collected during the annual September hunt, a male bias is not unexpected, because this harvest is timed such that most females with young will not be accessible to trappers (Elsey et al. 1994). Instead, predomi-nantly surplus adult males are harvested, limiting the incidental take of breeding females that occupy a different habitat (Elsey et al. 1994). Despite a harvest that se-lects for males, when the percentage of total males is compared with the percentage of total females at the 10 to 20 km (27.6% and 19.1%) and 20 to 30 km distances (14.5% and 10.3%), these differences were not as pronounced (Table 2). In fact, the longest distance traveled (90.2 km) was by a female. This female was initially marked on 10 August 2000, and recaptured on RWR on 17 October 2000 at a site 24.9 km from the initial capture. The alligator was then harvested on private wet-lands outside the refuge on 16 September 2003, some 65.2 km from where it was caught in October 2000. Clearly, a large portion of the total distance moved (90.2 km) occurred within the fi rst two months after capture. The total number of recoveries (n = 1045) by all methods (286 harvested on private wetlands outside the refuge boundaries, 551 recaptured alive on the refuge and released, and 208 recaptured on the refuge during the controlled nui-sance harvest) indicates 29.7% of marked individuals were recovered. These data support the long-held dogma that alligators have few predators, excepting other alligators (Rootes and Chabreck 1993b), after reaching a total length of about 60 cm (approximately two years of age). One factor that appears to facilitate the dispersal of alligators is fl ooding (Cha-breck 1965). High winds and strong currents caused by Hurricane Audrey in 1957 swept alligators northward from RWR for distances “ranging from three to ten miles” (4.8–16.1 km). For alligators marked in our study, a small number (between two and seven annually) were caught from 2001–2005 on privately owned wet-lands, north of RWR. Some of these had moved 10 to 20 km in the interval between being marked and recaptured. Following Hurricane Rita in late 2005, the number of marked alligators recovered in this area increased markedly to 22 in 2006. Another 15 were recovered north of RWR in 2007 (one recovered 33.9 km from the initial capture site), and 16 in 2008, one of which moved 39.8 km from the initial capture location. Some of these may have simply attained a harvestable size, having earlier moved onto privately owned wetlands when they were too small to be harvested. However, a far more likely explanation is that these alligators were pushed north-ward by the extensive storm surge of Hurricane Rita.

Table 2. Sex ratio of American Alligators marked on Rockefeller Wildlife Refuge, LA and later recaptured ≥10 km away, outside of the refuge boundaries.

Distance moved (km) Males Females

10.0–19.9 59 1320.0–29.9 31 730.0–39.9 8 340.0–49.9 4 250.0–59.9 0 060.0–69.9 0 070.0–79.9 0 080.0–99.9 1 1


A few previous reports of long-distance movements by individual adult al-ligators are available. A 1.5-m female alligator fi rst captured on Wasaw Island, GA was seen on Hilton Head Island 15 days later, a straight-line distance of >50 km (Tamarack 1989). Similarly, Joanen and McNease (1972) and Elsey (2005) documented individual alligator movements of 53 km and 63 km, respectively. In contrast to adult alligators, there is a notable paucity of published data con-cerning long-distance movements by juveniles. The distances moved by some juvenile alligators in our study exceed previous estimates by a wide margin. One juvenile was captured >90 km and another >80 km from site of fi rst capture; several others moved >40 km. These fi ndings are consistent with earlier studies by Chabreck (1965) and Hines et al. (1968) that found juvenile alligators move greater distances than adults. However, at the time of fi nal capture, some juveniles in our study had attained adult size; therefore, it is possible that some long-distance movements occurred after these alligators reached sexual maturity. Of note, in May 2007, we incidentally recovered an immature (total length = 103 cm) nuisance alli-gator, which had moved >80 km from the site of its initial capture on 20 May 2002. A long-term study of C. crocodilus in the Brazilian Pantanal reported move-ments of up to 18 km in males and 16 km in females over a 15-year period (Campos et al. 2006). Direct comparison with our study is not possible, because this tropical habitat differs markedly from coastal south Louisiana by having distinct wet and dry seasons and widespread fl ooding in the wet season. During the dry season, caiman are restricted to small pools and rivers, but during the wet season they are able to disperse throughout the fl ooded Pantanal. However, similar to our study, smaller caiman moved greater distances than larger caiman, and there was a signifi cant positive relationship between the number of days from fi rst capture to distance moved (Campos et al. 2006). Long-distance movements by adult crocodiles are well documented. Allen (1974) estimated that a large adult male Crocodylus porosus Schneider (Es-tuarine Crocodile) observed on Ponape, Eastern Caroline Islands had traveled >1300 km across open ocean. Juvenile and sub-adult C. porosus disperse long distances up and down river systems in northern Australia (Kay 2004, Webb and Messel 1978). It is diffi cult to compare marsh-dwelling alligators with crocodiles inhabiting rivers, but most species of crocodilians appear to exhibit a pattern of juvenile dispersal, usually beginning one to two years after hatching (Chabreck 1965, Cintra 1989, Dietz 1979). Dispersal in juvenile Crocodylus johnstoni Krefft (Australian Freshwater Crocodile) was studied by Tucker et al. (1997, 1998). Similar to alligators, immature C. johnstoni had larger home ranges than adults, and males approaching sexual maturity entered a “nomadic” phase before establishing an adult home range (Tucker et al. 1998). Earlier studies indicated that juvenile alligators have larger home ranges than adults (McNease and Joanen 1974, Taylor et al. 1976). However, movements of 30 to 90 km are clearly too large to be considered part of the home range of a juve-nile alligator. The fact that smaller alligators moved greater distances than larger alligators suggests that juveniles are less able to defend a territory from larger con-specifi cs. Aggression towards juveniles and even cannibalism by adults is known to occur in crocodilians (Cott 1961, Hunt 1977, McNease and Joanen 1977, Rootes


and Chabreck 1993b). It is unlikely that juvenile crocodilians actually have large home ranges; instead, the reportedly larger home ranges may be dispersal events that occur when juveniles are driven out of an area by adults. In conclusion, our long-term study clearly documents the great distances al-ligators move over extended periods. Although many alligators remain within a relatively small area for long periods of time, others move unusually long dis-tances. Additional research may provide information on why alligators select one location over another, despite similar habitat and prey availability.

Acknowledgments

We thank Lisa Morris of Louisiana State University for help with the statistics and nu-merous LDWF employees for assistance with capture and sampling of alligators at night and collection of harvest data in the fi eld, especially Dwayne LeJeune, Jeb Linscombe, George Melancon, and Karen McCall.

Literature Cited

Allen, G.R. 1974. The marine crocodile, Crocodylus porosus, from Ponape, Eastern Caroline Islands, with notes on food habits of crocodiles from the Palau Archipelago. Copeia 1974:553.

Campos, Z., M. Coutinho, G. Mourão, P. Bayliss, and W.E. Magnusson. 2006. Long-distance movement by Caiman crocodilus yacare: Implications for management of the species in the Brazilian Pantanal. Herpetological Journal 16:123–132.

Chabreck, R.H. 1965. The movement of alligators in Louisiana. Proceedings of the Southeastern Association of Game and Fish Commissioners 19:102–110.

Cintra, R. 1989. Maternal care and daily pattern of behavior in a family of caimans, Cai-man yacare in the Brazilian Pantanal. Journal of Herpetology 23:320–322.

Cott, H.B. 1961. Scientifi c results of an inquiry into the ecology and economic status of the Nile Crocodile (Crocodilus niloticus) in Uganda and Northern Rhodesia. Transac-tions of the Zoological Society of London 29:211–356.

Dietz, D.C. 1979. Behavioral ecology of young American Alligators. Ph.D. Dissertation, University of Florida, Gainesville, FL. 152 pp.

Elsey, R.M. 2005. Unusual offshore occurrence of an American Alligator. Southeastern Naturalist 4:533–536.

Elsey, R.M., T. Joanen, and L. McNease. 1994. Louisiana's alligator research and man-agement program: An update. Pp. 199–229, In Proceedings of the 12th Working Meeting of the Crocodile Specialist Group. IUCN Publications, Gland, Switzerland. 304 pp.

Elsey, R.M., L. McNease, and T. Joanen. 2000. Louisiana’s alligator ranching pro-gramme: A review and analysis of releases of captive-raised juveniles. Pp. 426–441, In G.C. Grigg, F. Seebacher, and C.E. Franlin (Eds.). Crocodilian Biology and Evolu-tion. Surrey Beatty and Sons, NSW, Australia. 446 pp.

Hines, T.C., M.J. Fogarty, and L.C. Chappell. 1968. Alligator research in Florida: A progress report. Proceedings of the Southeastern Association of Game and Fish Com-missioners 22:166–180.

Hunt, R.H. 1977. Aggressive behavior by adult Morelet’s Crocodiles, Crocodylus more-letii, toward young. Herpetologica 33:195–201.

Joanen, T., and L. McNease. 1970. A telemetric study of nesting female alligators on Rockefeller Refuge, Louisiana. Proceedings of the Southeastern Association of Game and Fish Commissioners 24:175–193.


Joanen, T., and L. McNease. 1972. A telemetric study of adult male alligators on Rock-efeller Refuge, Louisiana. Proceedings of the Southeastern Association of Game and Fish Commissioners 26:252–275.

Kay, W.R. 2004. Movements and home ranges of radio-tracked Crocodylus porosus in the Cambridge Gulf region of Western Australia. Wildlife Research 31:495–508.

Keddy P.A., D. Campbell, T. McFalls, G.P. Shaffer, R. Moreau, C. Draguet, and R. Hele-niak. 2007. The wetlands of Lakes Ponchartrain and Maurepas: Past, present, and future. Environmental Review 15:43–77.

Lance, V.A., R.M. Elsey, and J.W. Lang. 2000. Sex ratios of American Alligators (Cro-codylidae): Male or female biased? Journal of Zoology 252:71–78.

Lance, V.A., D.C. Rostal, R.M. Elsey, and P.L. Trosclair III. 2009. Ultrasonography of reproductive structures and hormonal correlates of follicular development in female American Alligators, Alligator mississippiensis, in southwest Louisiana. General and Comparative Endocrinology 162:251–256.

McNease, L., and T. Joanen. 1974. A study of immature alligators on Rockefeller Refuge, Louisiana. Proceedings of the Southeastern Association of Game and Fish Commis-sioners 28:482–500.

McNease, L., and T. Joanen. 1977. Alligator diets in relation to marsh salinity. Proceed-ings of the Southeastern Association of Fish and Wildlife Agencies 31:36–40.

Rootes, W.L. 1989. Behavior of the American Alligator in a Louisiana freshwater marsh. Ph.D. Dissertation. Louisiana State University, Baton Rouge, LA. 84 pp.

Rootes, W.L., and R.H. Chabreck. 1993a. Reproductive status and movement of adult female alligators. Journal of Herpetology 27:121–126.

Rootes, W.L., and R.H. Chabreck. 1993b. Cannibalism in the American Alligator. Her-petologica 49:99–107.

Tamarack, J.L. 1989. Georgia’s coastal alligators, variation in habitat and prey avail-ability. Pp. 105–118, In Proceedings of the 8th Working Meeting of the Crocodile Specialist Group. IUCN Publications, Gland, Switzerland. 405 pp.

Taylor, D. 1984. Management implications of an adult female telemetry study. Proceed-ings of the Southeastern Association of Fish and Wildlife Agencies 38:222–227.

Taylor, D., T. Joanen, and L. McNease. 1976. A comparison of native and introduced im-mature alligators in northeast Louisiana. Proceedings of the Southeastern Association of Fish and Wildlife Agencies 30:362–370.

Tucker, A.D., C.J. Limpus, H.I. McCallum, and K.R. McDonald. 1997. Movements and home ranges of Crocodylus johnstoni in the Lynd River, Queensland. Wildlife Re-search 24:379–396.

Tucker, A.D., H.I. McCallum, C.J. Limpus, and K.R. McDonald. 1998. Sex-biased dis-persal in a long-lived polygynous reptile (Crocodylus johnstoni). Behavioral Ecology and Sociobiology 44:85–90.

Webb, G.J.W., and H. Messel. 1978. Movement and dispersal patterns of Crocodylus poro-sus in some rivers of Arnem land, northern Australia. Wildlife Research 5:263–283.

Zippel, K.C., H.B. Lillywhite, and C.R.J. Mladinich. 2003. Anatomy of the crocodilian spinal vein. Journal of Morphology 258:327–335.

long-distance movement by american alligators in southwest ... · 2011 southeastern naturalist...

Documents