Alligator Nests Research Articles

American Black Bears Depredate American Alligator Nests in South Florida

American Black Bears Depredate American Alligator Nests in South Florida

Incubation determines favorable microbial communities in Chinese alligator nests.

Nest materials are a major heat source due to rotting promoted by microbial activity. Additionally, they are a potential microbial source given their direct contact with eggshells. Microbial dynamics during incubation have been studied in wild birds; however, similar studies in reptiles remain elusive. Here, the study characterized microbial communities in the nest materials of Chinese alligator (Alligator sinensis) using high-throughput sequencing of bacterial 16S rRNA genes and fungal internal transcribed spacer (ITS) region sequences. The results showed that significant changes in the diversity and structure of microbial communities according to different incubation periods. The diversity and richness of bacterial species increased significantly over time, but the relative abundance of the most dominant bacteria in pre-incubation period, including some pathogenic bacteria, declined after incubation. In contrast, fungal species diversity and richness decreased significantly with time. Additionally, nest material composition significantly influenced microbial community structure rather than species diversity and richness. Notably, the fungal community structure showed a stronger response than bacteria to nest material composition, which varied due to differences in plant litter composition. Our results demonstrate the significant response of microbial community diversity and structure to differences in incubation periods and nest material composition in reptiles. It is further emphasized that the importance of incubation period in the conservation of the Chinese alligator and could inform similar studies in other reptiles and birds.

Wetland Habitat Characteristics Predict Nest Site Selection of American Alligators (Alligator mississippiensis) in an Inland Freshwater Ecosystem

Habitat characteristics can have large effects on nest site selection of oviparous vertebrates. It is thought that habitat preference in many species is driven by natural selection because of habitat-specific fitness consequences. However, long-term studies on nesting of oviparous reptiles, in particular, are less common in comparison with other nesting vertebrates. As a result, specific habitat associations that define nesting habitat for many species are largely unknown. We studied habitat characteristics and selection of American Alligator (Alligator mississippiensis) nest sites in inland freshwater wetlands. We investigated the habitat characteristics associated with 112 nests studied during the 2013–2019 nesting seasons, and quantified habitat characteristics in relation to nest locations and random points. A nearest neighbor analysis indicated that American Alligator nests are not randomly distributed across wetlands, but are more representative of a clumped spatial distribution, suggestive of habitat preference and site selection. We measured habitat variables such as wetland vegetation cover, average water depth, island density, bank slope, canopy cover, and wet bulb globe temperature, as well as alligator population demographics such as relative adult proportion, at each nest and random site. Subsequently, we found that the best variables for predicting American Alligator nest site selection included island density, slope of bank, canopy cover, and wet bulb globe temperature. The best predictive model demonstrated that the odds of nest site selection increased with increasing canopy cover, wet bulb globe temperature, island density, and decreasing bank slope. These habitat choices presumably reduce the risk of nest predation and provide thermal cover for proper balance of nest site microclimate. Based on our results, practices focused on alligator nesting habitat should consider these specific habitat characteristics in outlining applied strategies and working toward management and conservation goals.

Evaluation of Effects of Harvest on Alligator Populations in Louisiana

ABSTRACTBiologists with the Louisiana Department of Wildlife and Fisheries, Louisiana, USA, have managed statewide annual harvest of alligators (Alligator mississippiensis) for 35 years (1981–present). We collected and analyzed harvest data for Louisiana alligators to determine the effects of harvest on the population structure, focusing on the larger size classes (≥274 cm) of this slow‐growing species. Linear regression analyses revealed that body size‐class structure, based on overall average size and the percentage of animals harvested in the larger size classes was relatively stable. Annual aerial alligator nest counts indicated a continual growth of the population, and over time harvested alligators maintained a constant average size. Analyses of population size (based on number of nests and population modeling) indicated that the current annual harvest represents approximately 3% of the population. Linear regression analysis showed that annual hunter success declined only slightly during the study period, and the scheduling of the hunt season after the hatch period and recommended hunting in areas not frequented by breeding females provides economic opportunities for hunters to participate in a sustainable harvest that preserves the larger size classes of alligators in the population. Strict enforcement of existing laws was a key factor responsible for the success of this harvest program. Comparison of alligator population size and number of harvest‐related citations indicated that illegal harvest did not have a negative effect on population size, and linear regression analyses revealed that the rate of increase in citations was lower than the increase in populations over the study period. The results of this harvest program indicated that alligators can be hunted in a sustainable manner if hunting is conducted after the hatch period and occurs in areas that primarily exclude the harvest of adult females, and strict law enforcement curbs illegal activities that negatively affect populations. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.

Microbial Assemblage Dynamics Within the American Alligator Nesting Ecosystem: a Comparative Approach Across Ecological Scales.

Understanding the ecological processes that shape species assemblage patterns is central to community ecology. The effects of ecological processes on assemblage patterns are scale-dependent. We used metabarcoding and shotgun sequencing to determine bacterial taxonomic and functional assemblage patterns among varying defined focal scales (micro-, meso-, and macroscale) within the American alligator (Alligator mississippiensis) nesting microbiome. We correlate bacterial assemblage patterns among eight nesting compartments within and proximal to alligator nests (micro-), across 18 nests (meso-), and between 4 geographic sampling sites (macro-), to determine which ecological processes may drive bacterial assemblage patterns within the nesting environment. Among all focal scales, bacterial taxonomic and functional richness (α-diversity) did not statistically differ. In contrast, bacterial assemblage structure (β-diversity) was unique across all focal scales, whereas functional pathways were redundant within nests and across geographic sites. Considering these observed scale-based patterns, taxonomic bacterial composition may be governed by unique environmental filters and dispersal limitations relative to microbial functional attributes within the alligator nesting environment. These results advance pattern-process dynamics within the field of microbial community ecology and describe processes influencing the American alligator nest microbiome.

Examining maternal and environmental transfer of mercury into American alligator eggs.

American alligators are exposed to mercury (Hg) throughout their natural range and may maternally transfer Hg into their eggs. Wildlife species are highly sensitive to Hg toxicity during embryonic development and neonatal life, and information on Hg transfer into eggs is critical when attempting to understand the effects of Hg exposure on developing oviparous organisms. To examine Hg transfer in alligators, the objectives of the present study were to 1) determine Hg concentrations in yolk (embryonic and neonatal food source) from wild alligator eggs collected from three locations - Yawkey Wildlife Center SC (YWC), Lake Apopka FL (LA), and Lake Woodruff FL (LW); 2) examine the relationship between THg concentrations in wild alligator nest material and egg yolk at Merritt Island National Wildlife Refuge, FL; 3) examine the Hg concentrations in wild maternal female alligators (blood) and the THg in corresponding egg yolks and embryos across three nesting seasons at a single location (YWC), and evaluate the relationship between nesting female THg concentrations (blood) and their estimated age and number of nesting years (YWC); and 4) assess the transfer of biologically-relevant Hg concentrations (based on Hg measured in maternal female blood) into embryos using an egg-dosing experiment. Mean total Hg (THg) concentrations observed at each site were 26.3ng/g±11.0ng/g (YWC), 8.8ng/g±5.1ng/g (LA), and 22.6ng/g±6.3ng/g (LW). No relationship was observed between THg in alligator nest material and corresponding yolk samples, nor between THg in maternal alligator blood and estimated age and number of nesting years of these animals. However, significant positive relationships were observed between THg in blood of nesting female alligators and THg in their corresponding egg yolk. We observed that 12.8% of the maternal blood THg is found in the corresponding egg yolk, and a highly significant correlation was observed between the two sample types (r=0.66; p<0.0001). The egg dosing experiment revealed that Hg did not transfer through the eggshell at developmental stage 19. Overall, this study provides new information regarding Hg transfer in American alligators which can improve biomonitoring efforts and may inform ecotoxicological investigations and population management programs in areas of high Hg contamination.

Observations of an Alligator (Alligator mississippiensis) Nest and Behavior of Hatchlings in Clark County, with anecdotal observations of other Alligator Nests in Arkansas

Observations of an Alligator (Alligator mississippiensis) Nest and Behavior of Hatchlings in Clark County, with anecdotal observations of other Alligator Nests in Arkansas

Baseline Alligator Nesting Data in Arthur R. Marshall Loxahatchee National Wildlife Refuge to Inform Monitoring

Abstract Monitoring key ecological attributes helps land managers understand the current state of the resource and decide if management action is necessary. Baseline data on spatial and temporal variability of attributes to be monitored is important for development of successful monitoring programs. In this study, I collected data from 2000 to 2004 on American alligator Alligator mississippiensis nesting in the Arthur R. Marshall Loxahatchee National Wildlife Refuge to determine feasibility of conducting alligator nest surveys and collect baseline data on alligator nesting status and variability. I used nest data to provide examples of potential monitoring strategies for tracking trends over time or understanding the effects of different hydrologic conditions on alligator nesting. Conducting ground surveys with airboats in Arthur R. Marshall Loxahatchee National Wildlife Refuge proved to be an effective method of finding alligator nests. Number of nests per 1.6 km × 1.6 km (256-ha) plot ranged from 1 to 12, and by year from 28 to 53. Overall, average number of nests per hour ranged from 1.8 ± 0.26 (SE) in 2000 to a low of 0.84 ± 0.08 in 2004. Using data from this study for the six plots sampled each year, and assuming no change in variability, power analysis shows that 10 y of sampling would allow for detection of an annual 10% change in number of nests per hour, with power and level of certainty set equal at 90% (β and α both 0.10). Additionally, 15 y of data would allow for a detection of a 5% change per year. Thirty-seven plots per area would be necessary to assess a 40% difference in number of alligator nests per hour in areas with different hydrologic conditions with power and level of certainty at 90%. Land managers can use these data and analyses, along with examples of monitoring strategies, to guide development of more specific monitoring protocols that address restoration objectives and management actions throughout the Florida Everglades.

Nest Attendance Patterns in the American Alligator (Alligator mississippiensis)

The behavioral variation in alligator nest attendance has characterized the species as iconic in common lore and perplexed biologists for decades. Here, we quantify patterns in nest attendance among mothers as well as variation in such patterns throughout two nesting seasons. We employed camera traps controlled by circuit boards to capture time-lapse photographs of alligator nest areas for the duration of each nesting season. Data revealed a bimodal pattern of nest attendance over time that significantly varied across incubation days in both 2011 and 2012, and also differed between years. Nest attendance also differed among hours in the diel cycle, and this pattern was the same for both years. Nest visits were frequent immediately after the eggs were laid, and attendance behavior attenuated rapidly after the first week of incubation. Nest visitation then increased near the end of the incubation period with the largest portion of visits recorded during hatching and the maternal movement of hatchlings away ...

Commensal Nesting ofScincella lateralis(Little Brown Skinks) inAlligator mississippiensis(American Alligator) Nests andOndatra zibethicus(Muskrat) Houses in Southwestern Louisiana

Abstract Scincella lateralis (Little Brown Skink, hereafter Skink) are ubiquitous throughout the southeastern US and primarily nest in leaf litter on the forest floor. However, their presence in coastal marsh settings necessitates their use of alternate nesting habitats. We investigated Skink nesting ecology in Alligator mississippiensis (American Alligator) nests and Ondatra zibethicus (Muskrat) houses in an intermediate/brackish coastal marsh habitat at Rockefeller Wildlife Refuge in southwestern Louisiana. For our field studies, we found and collected Skink eggs from 16 June through 5 October, and hatched eggshells from 6 July through 5 October. We found Skink eggs/eggshells in 36 of 109 active American Alligator nests (33.0%), 19 of 36 inactive Alligator nests (52.8%), and 13 of 51 Muskrat houses (25.5%). Clutch size ranged from 1 to 5 eggs (average = 3.0). The mean depth of Skink eggs was 24.6 cm in American Alligator nests and 17.1 cm in Muskrat houses. Multiple clutches commonly occurred in a struc...

The Use of an Unmanned Aerial Vehicle to Locate Alligator Nests

Abstract Coastal marshes of Louisiana provide nesting habitat for Alligator mississippiensis (American Alligator). Helicopters are typically used to locate Alligator nests in remote interior marshes. We tested the use of an unmanned aerial vehicle (UAV) to detect Alligator nests on Rockefeller Wildlife Refuge in Grand Chenier, LA. Three brief flights with a combined search time of approximately 25 minutes and 9 seconds were conducted in a single afternoon, covering 28.2 ha. While in the field, we observed 6 Alligator nests with the UAV, and later review of video imagery recorded allowed us to detect an additional 6 Alligator nests. The use of UAVs may be a useful tool for detecting Alligator nests.

Tupinambis merianae as nest predators of crocodilians and turtles in Florida, USA

Tupinambis merianae, is a large, omniv- orous tegu lizard native to South America. Two populations of tegus are established in the state of Florida, USA, but impacts to native species are poorly documented. During summer 2013, we placed auto- mated cameras overlooking one American alligator (Alligator mississippiensis) nest, which also contained a clutch of Florida red-bellied cooter (Pseudemys nelsoni) eggs, and one American crocodile (Crocody- lus acutus) nest at a site in southeastern Florida where tegus are established. We documented tegu activity and predation on alligator and turtle eggs at the alligator nest, and tegu activity at the crocodile nest. Our finding that one of the first two crocodilian nests to be monitored was depredated by tegus suggests that tegus should be further evaluated as a threat to nesting reptiles in Florida.

The reproductive hormone cycle of adult female American alligators from a barrier island population

Comparatively, little data are available detailing the geographic variation that exists in the reproductive endocrinology of adult alligators, especially those living in barrier islands. The Merritt Island National Wildlife Refuge (MI) is a unique barrier island environment and home to the Kennedy Space Center (FL, USA). Seasonal patterns of sex steroids were assessed in adult female American alligators from MI monthly from 2008 to 2009, with additional samples collected at more random intervals in 2006, 2007, and 2010. Plasma 17β-estradiol and vitellogenin concentrations peaked in April, coincident with courtship and mating, and showed patterns similar to those observed in adult female alligators in other regions. Plasma concentrations of progesterone, however, showed patterns distinctly different than those reported for alligator populations in other regions and remained relatively constant throughout the year. Plasma DHEA peaked in July around the time of oviposition, decreased in August, and then remained constant for the remaining months, except for a moderate increase in October. Circulating concentrations of DHEA have not been previously assessed in a female crocodilian, and plasma concentrations coincident with reproductive activity suggest a reproductive and/or behavioral role. Interestingly, plasma testosterone concentrations peaked in May of 2008, as has been shown in female alligator populations in other regions, but showed no peak in 2009, demonstrating dramatic variability from year to year. Surveys showed 2009 to be particularly depauperate of alligator nests in MI, and it is possible that testosterone could serve as a strong indicator of breeding success.

The influence of regional hydrology on nesting behavior and nest fate of the American alligator

AbstractHydrologic conditions are critical to the nesting behavior and reproductive success of crocodilians. In South Florida, USA, growing human settlement has led to extensive surface water management and modification of historical water flows in the wetlands, which have affected regional nesting of the American alligator (Alligator mississippiensis). Although both natural and anthropogenic factors are considered to determine hydrologic conditions, the aspects of hydrological patterns that affect alligator nest effort, flooding (partial and complete), and failure (no hatchling) are unclear. We deconstructed annual hydrological patterns using harmonic models that estimated hydrological matrices including mean, amplitude, timing of peak, and periodicity of surface water depth and discharge and examined their effects on alligator nesting using survey data from Shark Slough, Everglades National Park, from 1985 to 2005. Nest effort increased in years with higher mean and lesser periodicity of water depth. A greater proportion of nests were flooded and failed when peak discharge occurred earlier in the year. Also, nest flooding rates were greater in years with greater periodicity of water depth, and nest failure rate was greater when mean discharge was higher. This study guides future water management decisions to mitigate negative impacts on reproduction of alligators and provides wildlife managers with a tool for assessing and modifying annual water management plans to conserve crocodilians and other wetland species. © 2012 The Wildlife Society.

Nest success and hatchling survival of American alligators within inland wetlands of east Texas

AbstractBecause of liberalization of American alligator (Alligator mississippiensis) harvest management in Texas, estimates of nest success and hatchling survival for inland populations are essential for long‐term, sustainable population and harvest management. To date, few studies have examined American alligator nest success and hatchling survival. We initiated a 3‐year study from 2006 to 2008 to document alligator nest success and hatchling survival within several wetlands in east Texas. From June 2006 to August 2008, we located 30 nests from 3 wetlands within east Texas, where overall nest success was 44.2% (95% CI = 25.1–63.1%), irrespective of year. Nest circumference and day during the nesting season exerted the greatest influence on nest success. Additionally, from August 2006 to August 2008 we captured, marked, and released 271 hatchling alligators at Little Sandy National Wildlife Refuge, and recaptured an additional 192 hatchling alligators during this time. We estimated yearly apparent survival at 6.0% (95% CI = 2.0–14.6%) for hatchling alligators born in 2006 and 43.0% (95% CI = 28.4–57.8%) for those hatched in 2007. Variation in nest success and hatchling survival was likely attributed to fluctuating water levels and habitat management practices. Alligator harvest regulations need to account for variability in nest success and hatchling survival by including site‐specific estimates of these metrics into harvest models. Failing to account for spatial and temporal variation in nest success and hatchling survival may result in unsustainable harvest and/or overharvest. © 2012 The Wildlife Society.

Effects of Feral Swine (Sus scrofa) on Alligator (Alligator mississippiensis) Nests in Louisiana

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 repo...

Report of case: leptospirosis after exposure to alligator carcass

In the past decade, leptospirosis has emerged as a globally important infectious disease. Mortality remains significant; this may be related to delays in diagnosis because of lack of infrastructure and adequate clinical suspicion, and to other poorly understood reasons that may include inherent pathogenicity of some leptospiral strains or genetically determined host immunopathological responses. Leptospirosis is a spirochete parasitic bacterium most commonly reported from rodents and contracted through contact with rodent urine, but also reported from cows and other domestic animals and contracted through contact with contaminated water. Humans are infected by direct contact with animals or through exposure to fresh water or soil contaminated by infected animal urine. Leptospires enter the body through cuts and abrasions, mucous membranes or conjunctivae, or aerosol inhalation of microscopic droplets. From 1995-1998, approximately nine people working with alligators in south Florida have apparently contracted leptospirosis. All of the victims were working with wild alligators; most had contact with alligator nests and nearly half required hospitalization. Although it has been postulated that leptospires may be transmitted directly from infected, large reptiles to the hands of handlers, it has been felt that it was probably more likely that handlers were indirectly exposed by water contaminated with the urine of leptospiruric reptiles or that the swamps and waterways from which eggs are harvested are contaminated by the infected urine of rodents or other animals. This report describes a case in which a Florida State Trooper became symptomatic after removal of an alligator carcass from a south Florida roadway.

Multiyear multiple paternity and mate fidelity in the American alligator,Alligator mississippiensis

We examined multiple paternity during eight breeding events within a 10-year period (1995-2005) for a total of 114 wild American alligator nests in Rockefeller Wildlife Refuge in south-west Louisiana. Our goals included examining (i) within population variation in multiple paternity among years, (ii) variation in multiple paternity in individual females and (iii) the potential for mate fidelity. To accomplish this, in the current study, eggs were sampled from 92 nests over 6 years and analysed along with 22 nests from a previous 2-year study. Genotypes at five microsatellite loci were generated for 1802 alligator hatchlings. Multiple paternity was found in 51% of clutches and paternal contributions to these clutches were highly skewed. Rates of multiple paternity varied widely among years and were consistently higher in the current study than previously reported for the same population. Larger females have larger clutches, but are not more likely to have multiply sired nests. However, small females are unlikely to have clutches with more than two sires. For 10 females, nests from multiple years were examined. Seven (70%) of these females exhibited long-term mate fidelity, with one female mating with the same male in 1997, 2002 and 2005. Five females exhibiting partial mate fidelity (71%) had at least one multiple paternity nest and thus mated with the same male, but not exclusively. These patterns of mate fidelity suggest a potential role for mate choice in alligators.

Possible Generational Effects of Habitat Degradation on Alligator Reproduction

ABSTRACT Population decline of the American alligator (Alligator mississippiensis) was observed in Lake Apopka in central Florida, USA, in the early 1980s. This decline was thought to result from adult mortality and nest failure caused by anthropogenic increases in sediment loads, nutrients, and contaminants. Reproductive impairment also was reported. Extensive restoration of marshes associated with Lake Apopka has been conducted, as well as some limited restoration measures on the lake. Monitoring by the Florida Fish and Wildlife Conservation Commission (FFWCC) has indicated that the adult alligator population began increasing in the early 1990s. We expected that the previously reported high proportion of complete nest failure (θ0) during the 1980s may have decreased. We collected clutches from alligator nests in Lake Apopka from 1983 to 2003 and from 5 reference areas from 1988 to 1991, and we artificially incubated them. We used a Bayesian framework with Gibbs sampler of Markov chain Monte Carlo simulation to analyze θ0. Estimated θ0 was consistently higher in Lake Apopka compared with reference areas, and the difference in θ0 ranged from 0.19 to 0.56. We conducted change point analysis to identify and test the significance of the change point in θ0 in Lake Apopka between 1983 and 2003, indicating the point of reproductive recovery. The estimated Bayes factor strongly supported the single change point hypothesis against the no change point hypothesis. The major downward shift in θ0 probably occurred in the mid‐1990s, approximately a generation after the major population decline in the 1980s. Furthermore, estimated θ0 values after the change point (0.21) were comparable with those of reference areas (0.07–0.31). These results combined with the monitoring by FFWCC seem to suggest that anthropogenic habitat degradation caused reproductive impairment of adult females and decreases in θ0 occurred with the sexual maturity of a new generation of breeding females. Long‐term monitoring is essential to understand population changes due to habitat restoration. Such information can be used as an input in planning and evaluating restoration activities.

Multiple paternity and mating patterns in the American alligator, Alligator mississippiensis.

Eggs were sampled from 22 wild American alligator nests from the Rockefeller Wildlife Refuge in south-west Louisiana, along with the females guarding the nests. Three nests were sampled in 1995 and 19 were sampled in 1997. Females and offspring from all clutches were genotyped using five polymorphic microsatellite loci and the three nests from 1995 were also genotyped using one allozyme locus. Genotypes of the hatchlings were consistent with the guarding females being the mothers of their respective clutches. Multiple paternity was found in seven of the 22 clutches with one being fathered by three males, and the remaining six clutches having genotypes consistent with two males per clutch. Paternal contributions of multiply sired clutches were skewed. Some males sired hatchlings of more than one of the 22 clutches either as one of two sires of a multiple paternity clutch, as the sole sire of two different clutches, or as the sole sire of one clutch and one of two sires of a multiply sired clutch. There was no significant difference between females that had multiple paternity clutches and those that had singly sired clutches with respect to female total length (P = 0.844) and clutch size (P = 0.861). Also, there was no significant correlation between genetic relatedness of nesting females and pairwise nest distances (r2 = 0.003, F1,208 = 0.623, P = 0.431), indicating that females in this sample that nested close to one another were no more related than any two nesting females chosen at random. Eleven mutations were detected among hatchlings at the five loci over the 22 clutches. Most of these mutations (eight of 11) occurred at Ami(mu)-17, the only compound microsatellite locus of the five used in this study, corresponding to a mutation rate of 1.7 x 10-3. Finally, most of the mutations (82%) were homoplasious, i.e., mutating to an allelic state already present in this Louisiana population.