Merritt Island National Wildlife Refuge Research Articles

Striped Mullet Migration Patterns in the Indian River Lagoon: A Network Analysis Approach to Spatial Fisheries Management

AbstractStriped Mullet Mugil cephalus are numerically abundant forage fish, highly valuable as prey, and commercially valuable to humans. From September to December, Striped Mullet in the Indian River Lagoon (IRL), Florida, undergo an annual migration from inshore foraging habitats to oceanic spawning sites. However, their migratory pathways—particularly their intra‐estuarine movement pathways—remain unknown. To address this knowledge gap, we utilized passive acoustic telemetry to assess the movement patterns of Striped Mullet within the IRL. Thirty‐two fish were tagged, generating usable tracks from 18 individuals. The mean (±SD) time that fish were detected in the array was about 38 ± 90 d, with the longest detection period being 444 d. We also document the first evidence of skipped spawning in Striped Mullet inhabiting waters of the southeastern United States. These data suggest that impoundments around the Merritt Island National Wildlife Refuge serve as important refugia for Striped Mullet, while the Banana and Indian rivers act as corridors during their inshore migratory movements. Through spatial fisheries management, high‐value habitat and connective elements utilized by Striped Mullet and other vital forage fish may be identified so as to benefit both natural and human dynamics in estuarine systems.

Nonlinear patterns in mercury bioaccumulation in American alligators are a function of predicted age

Mercury is a widespread, naturally occurring contaminant that biomagnifies in wetlands due to the methylation of this element by sulfate-reducing bacteria. Species that feed at the top trophic level within wetlands are predicted to have higher mercury loads compared to species feeding at lower trophic levels and are therefore often used for mercury biomonitoring. However, mechanisms for mercury bioaccumulation in sentinel species are often poorly understood, due to a lack of long-term studies or an inability to differentiate between confounding variables. We examined mercury bioaccumulation patterns in the whole blood of American alligators (Alligator mississippiensis) from a long-term mark-recapture study (1979–2017) in South Carolina, USA. Using a growth model and auxiliary information on predicted age at first capture, we differentiated between age- and size-related variation in mercury bioaccumulation, which are often confounded in alligators due to their determinate growth pattern. Contrary to predictions that the oldest or largest individuals were likely to have the highest mercury concentrations, our best-supported model indicated a peak in mercury concentration at 30–40 years of age, depending on the sex, and lower concentrations in the youngest and oldest animals. To evaluate the robustness of our findings, we re-analyzed data from a previously published study of mercury in alligators sampled at Merritt Island National Wildlife Refuge in Florida. Unlike the South Carolina data, the data from Florida contained minimal auxiliary information regarding age, yet the best supported model similarly indicated a peaked rather than increasing relationship between mercury and body size, a less-precise indicator of age. These findings highlight how long-term monitoring can differentiate between confounding variables (e.g., age and size) to better elucidate complex relationships between contaminant exposure and demographic factors in sentinel species.

Tipping Points in the Mangrove March: Characterization of Biogeochemical Cycling Along the Mangrove–Salt Marsh Ecotone

Coastal wetland vegetation communities can respond to sea level rise via the encroachment of more salt- and inundation-tolerant species into existing vegetation communities. Black mangroves (Avicennia germinans L.) are encroaching on saltgrass (Distichlis spicata L.) within the Merritt Island National Wildlife Refuge in east central Florida (USA). Nine soil cores collected along three transects captured the transitions of both perceived abiotic drivers (salinity and inundation) and vegetation communities during both high- and low-water seasons to investigate patterns in soil biogeochemical cycling of carbon (C), nitrogen (N), and phosphorus (P). Results showed no change in soil carbon dioxide production along the ecotone during either season, though changes in enzyme activity and mineralization rates of N and P could indicate changes in C quality and nutrient availability affecting C degradation along the ecotone. All parameters, excluding microbial biomass carbon, showed higher rates of activity or availability during the low-water season. Long-term soil nutrient stores (total C, N, P) were greatest in the saltgrass soils and similar between the mangrove and transition zone soils, indicating a ‘tipping point’ in biogeochemical function where the transition zone is functionally equivalent to the encroaching mangrove zone. Indicators of current biogeochemical cycling (that is, enzyme activity, potentially mineralizable N rates, and extractable ammonium concentrations) showed alterations in activity across the ecotone, with the transition zone often functioning with lower activity than within end members. These indicators of current biogeochemical cycling change in advance of full vegetation shifts. Increases in salinity and inundation were linked to mangrove encroachment.

Perfluorinated alkyl acids and fecundity assessment in striped mullet (Mugil cephalus) at Merritt Island national wildlife refuge

This study investigated wild caught striped mullet (Mugil cephalus) at Merritt Island National Wildlife Refuge (MINWR) for levels of 15 perfluoroalkyl acids (PFAA) in tandem with individual fecundity measurements (Oocyte sub-stage 2 late, n=42) and oocyte reproductive stages (Stages 1–5, n=128). PFAA measurements were quantified in striped mullet liver (n=128), muscle (n=49), and gonad (n=10). No significant negative impacts of liver PFAA burden on wild-caught, mullet fecundity endpoints were observed in this study; however, changes in PFAA were observed in the liver as mullet progressed through different sub-stages of oocyte development. Of the PFAA with significant changes by sub-stage of oocyte development, the carboxylic acids (perfluorooctanoic acid, perfluorononanoic acid, and perfluorotridecanoic acid) increased in the liver with increasing sub-stage while the sulfonic acid and its precursor (perfluorooctanesulfonic acid (PFOS) and perfluorooctanesulfonamide, respectively) decreased in the liver with increasing sub-stage of oocyte development. This is a unique find and suggests PFAA change location of compartmentalization as mullet progress towards spawning. Investigations also revealed higher than expected median muscle and gonad levels of PFOS in striped mullet collected at MINWR (9.01ng/g and 80.2ng/g, respectively).

Set AHDriFT: Applying game cameras to drift fences for surveying herpetofauna and small mammals

ABSTRACTThe use of game cameras by wildlife biologists and managers to survey wildlife, particularly medium‐ and large‐bodied mammals, has increased dramatically. Previous attempts to survey small mammals and ectotherms have had limited detection success or were focused solely on a single species. We describe the Adapted‐Hunt Drift Fence Technique (AHDriFT), which combines commercially available game cameras and traditional drift fences to survey reptiles, amphibians, and small mammals. Across 4,502 trap‐nights at the Merritt Island National Wildlife Refuge, Florida, USA (Jun 2014 to Jun 2015), we recorded images for 2,523 unique vertebrate detections (2% unidentifiable) averaging 0.56 unique triggers/night. Using AHDriFT enables long‐duration surveys with high detectability while minimizing observer time. Guide‐boards increased terrestrial vertebrate image capture at minimal cost. During 1 year of usage, no mortality was documented using this camera‐trap system and field time was reduced by 95%, requiring only monthly visits of approximately 3 hr for 9 fence arrays to download images from the camera systems, compared with pitfall or funnel traps that require at least daily monitoring. © 2017 The Wildlife Society.

Evaluating mercury concentrations and body condition in American alligators (Alligator mississippiensis) at Merritt Island National Wildlife Refuge (MINWR), Florida

Concentrations of mercury (Hg) are not well studied in free-ranging wildlife. Atmospheric deposition patterns of Hg have been studied in detail and have been modeled for both global and specific locations and often correlate to environmental impact. However, monitoring the impact of Hg deposition in wildlife is complicated due to local environmental conditions that can affect the transformation of atmospheric Hg to the biologically available forms (e.g., rainfall, humidity, pH, the ability of the environment to methylate Hg), as well as affect the accessibility to organisms for sampling. In this study, Hg concentrations in blood samples from a population of American alligators (Alligator mississippiensis) at Merritt Island National Wildlife Refuge (MINWR), FL, USA, over a seven-year period (2007 to 2014; n=174 individuals) were examined to assess Hg variation in the population, as well as the difference in Hg concentration as a function of health status. While most of this population is healthy, 18 individuals with low body mass indices (BMI, defined in this study) were captured throughout the sampling period. These alligators exhibited significantly elevated Hg concentrations compared to their age/sex/season matched counterparts with normal BMI, suggesting that health status should be taken into account when examining Hg concentrations and effects. Alligator blood Hg concentrations were related to the interaction of age/size, sex, and season. This study illustrates the value of a routinely monitored population of large predators in a unique coastal wetland ecosystem, and illuminates the value of long-term environmental exposure assessment.

Impacts of mangrove encroachment and mosquito impoundment management on coastal protection services

The ecosystem services afforded by coastal wetlands are threatened by climate change and other anthropogenic stressors. The Kennedy Space Center and Merritt Island National Wildlife Refuge in east central Florida offer a representative site for investigating how changes to vegetation distribution interact with management to impact coastal protection. Here, salt marshes are converting to mangroves, and mosquito impoundment structures are being modified. The resulting changes to vegetation composition and topography influence coastal protection services in wetlands. We used a model-based assessment of wave attenuation and erosion to compare vegetation (mangrove, salt marsh) and impoundment state (intact, graded). Our findings suggest that the habitat needed to attenuate 90% of wave height is significantly larger for salt marshes than mangroves. Erosion prevention was significantly higher (470%) in scenarios with mangroves than in salt marshes. Intact berms attenuated waves over shorter distances, but did not significantly reduce erosion. Differences in coastal protection were driven more by vegetation than by impoundment state. Overall, our findings reveal that mangroves provide more coastal protection services, and therefore more coastal protection value, than salt marshes in east central Florida. Other coastal regions undergoing similar habitat conversion may also benefit from increased coastal protection in the future.

Adapting coastal management to climate change: Mitigating our shrinking shorelines

ABSTRACTSea‐level rise due to climate change is a major threat to coastal ecosystems worldwide. Current management to reduce beach erosion often focuses on protecting human structures and research on effects on wildlife is lacking. Using a combination of hierarchical models and generalized linear models, we evaluated how the gopher tortoise (Gopherus polyphemus) colonized constructed dunes along coastal scrub at the Merritt Island National Wildlife Refuge, central Florida, USA. Over 2 years, we surveyed tortoise populations along natural dunes and 2 constructed dunes (completed in 2012 and in 2014) and estimated tortoise density each summer and winter. Our models indicated that tortoise density along the 2014 dune was comparable to that of natural dunes ( = 0–8 tortoises/ha), and density peaked at a mean of 21 tortoises/ha along the 2012 constructed dune. Gopher tortoises rapidly colonized constructed dunes, and dune construction may represent effective management against habitat loss for this species. © 2017 The Wildlife Society.

Variation in perfluoroalkyl acids in the American alligator (Alligator mississippiensis) at Merritt Island National Wildlife Refuge

This study aimed to quantify concentrations of fifteen perfluoroalkyl acids (PFAAs) in the plasma of American alligators (Alligator mississippiensis) inhabiting wetlands surrounding the Kennedy Space Center (KSC) in Florida, USA located at Merritt Island National Wildlife Refuge (MINWR). Approximately 10 male and 10 female alligators (ntotal = 229) were sampled each month during 2008 and 2009 to determine if seasonal or spatial trends existed with PFAA burden. PFOS represented the highest plasma burden (median 185 ng/g) and PFHxS the second highest (median 7.96 ng/g). While no significant seasonal trends were observed, unique spatial trends emerged. Many of the measured PFAAs co-varied strongly together and similar trends were observed for PFOS, PFDA, PFUnA, and PFDoA, as well as for PFOA, PFHxS, PFNA, PFTriA, and PFTA, suggesting more than one source of PFAAs at MINWR. Higher concentrations of PFOS and the PFAAs that co-varied with PFOS were collected from animals around sites that included the Shuttle Landing Facility (SLF) fire house and the Neil Armstrong Operations and Checkout (O&C) retention pond, while higher concentrations of PFOA and the PFAA that co-varied with PFOA were sampled from animals near the gun range and the old fire training facility. Sex-based differences and snout-vent length (SVL) correlations with PFAA burden were also investigated.

Perfluorinated alkyl acids in plasma of American alligators (Alligator mississippiensis) from Florida and South Carolina.

The present study aimed to quantitate 15 perfluoroalkyl acids (PFAAs) in 125 adult American alligators at 12 sites across the southeastern United States. Of those 15 PFAAs, 9 were detected in 65% to 100% of samples: perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnA), perfluorododecanoic acid, perfluorotridecanoic acid (PFTriA), perfluorotetradecanoic acid, perfluorohexanesulfonic acid (PFHxS), and perfluorooctane sulfonate (PFOS). Males (across all sites) showed significantly higher concentrations of 4 PFAAs: PFOS (p = 0.01), PFDA (p = 0.0003), PFUnA (p = 0.021), and PFTriA (p = 0.021). Concentrations of PFOS, PFHxS, and PFDA in plasma were significantly different among the sites in each sex. Alligators at both Merritt Island National Wildlife Refuge (FL, USA) and Kiawah Nature Conservancy (SC, USA) exhibited some of the highest PFOS concentrations (medians of 99.5 ng/g and 55.8 ng/g, respectively) in plasma measured to date in a crocodilian species. A number of positive correlations between PFAAs and snout-vent length were observed in both sexes, suggesting that PFAA body burdens increase with increasing size. In addition, several significant correlations among PFAAs in alligator plasma may suggest conserved sources of PFAAs at each site throughout the greater study area. The present study is the first to report PFAAs in American alligators, to reveal potential PFAA hot spots in Florida and South Carolina, and to provide a contaminant of concern when assessing anthropogenic impacts on ecosystem health. Environ Toxicol Chem 2017;36:917-925. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Variations in hepatic biomarkers in American alligators (Alligator mississippiensis) from three sites in Florida, USA

Sub-individual biomarkers are sub-lethal biological responses commonly used in the assessment of wildlife exposure to environmental contaminants. In this study, we examined the activity of glutathione-s-transferase (GST) and lactate dehydrogenase (LDH), and metallothionein (MT) concentrations among captive-raised alligator hatchlings, wild-caught juveniles, and wild-caught adults. Juveniles and adults were collected from three locations in Florida (USA) with varying degrees of contamination (i.e. Lake Apopka (organochlorine polluted site), Merritt Island National Wildlife Refuge (NWR) (metal polluted site), and Lake Woodruff NWR (reference site)). We examined whether changes in the response of these three biomarkers were age and sex dependent or reflected site-specific variations of environmental contaminants. Juvenile alligators from Merritt Island NWR had higher MT concentrations and lower GST activity compared to those from the other two sites. This outcome was consistent with higher metal pollution at this location. Sexually dimorphic patterns of MT and GST (F > M) were observed in juvenile alligators from all sites, although this pattern was not observed in adults. GST activity was lower in captive-raised alligators from Lake Apopka and Merritt Island NWR as compared to animals from Lake Woodruff NWR, suggesting a possible developmental modulator at these sites. No clear patterns were observed in LDH activity. We concluded that GST and MT demonstrate age and sex specific patterns in the alligators inhabiting these study sites and that the observed variation among sites could be due to differences in contaminant exposure.

Microspatial sampling reveals cryptic influences on gene flow in a threatened mammal

We studied the population structure and historical demography of the last remaining core population of the threatened southeastern beach mouse (SEBM; Peromyscus polionotus niveiventris) located on a federally protected barrier island complex at the Kennedy Space Center (KSC), Merritt Island National Wildlife Refuge (MINWR) and Cape Canaveral Air Force Station (CCAFS) in Florida, USA. Beach mice (N = 171) were collected from 33 trapping locations along 30 km of coastline on KSC/MINWR/CCAFS and were genotyped using 10 microsatellite loci. We found four genetic clusters of mice that likely form a metapopulation. Gene flow among clusters, assessed using assignment tests, was limited suggesting that human development can serve to inhibit dispersal of beach mice. However, when the presence of roads were examined as possible barriers to movement, gene flow appeared to be facilitated suggesting that removal of thick vegetation along roadsides increases movement. We used approximate Bayesian computation (ABC) to estimate divergence time among clusters and effective population sizes for each cluster and for the pre-divergence population. Results of ABC analyses suggest that barriers to movement likely formed following the construction of the John F. Kennedy Space Center beginning in the 1960s but that this has not heavily impacted the effective size of populations. Pre-divergence and contemporary effective sizes are similar, thus, population sizes likely remained relatively large over the last 50–100 years. The population of SEBM on KSC/MINWR/CCAFS appears to be a genetically diverse core population and individuals from this population will most likely be good candidates for any future reintroduction and translocation programs.

Development of a nonlethal health assessment for wild Red Drum using a health index.

Nonlethal methods are needed to assess the health of wild fish and quantify the robustness of the broader population. Results could be used to indicate exposure to various stressors, such as contaminants, infectious disease, external parasite loads, and fishing pressure, to monitor changes in fish population health over time. The wild Red Drum Sciaenops ocellatus population in the Kennedy Space Center Reserve of Merritt Island National Wildlife Refuge was used to develop a protocol to define the health of free-ranging fish using nonlethal techniques. This health index incorporated morphometric measurements, weight, an evaluation for external parasite fauna, notation of physical deformities, and the presence of lesions. A total of 126 adult Red Drum were collected using hook-and-line angling during prespawning (May), spawning (September and October), and postspawning (December) periods. All fish were released alive back into their environment. The nonlethal health assessment scored fish in the "healthy" range of the health index during the prespawning and spawning periods. Fish caught during the postspawning period scored slightly below this range. Parasite load contributed to the depressed score during the postspawning period. Fish collected in all sampling periods were rated on average as "excellent" for condition factor, which suggests that the sampled population in the reserve were thriving.

Examination of metals from aerospace-related activity in surface water samples from sites surrounding the Kennedy Space Center (KSC), Florida.

Metal contamination from Space Shuttle launch activity was examined using inductively coupled plasma-atomic emission spectroscopy in a two-tier study sampling surface water collected from several sites at the Kennedy Space Center (KSC) and associated Merritt Island National Wildlife Refuge in east central Florida. The primary study examined both temporal changes in baseline metal concentrations (19 metals) in surface water (1996 to 2009, 11 sites) samples collected at specific long-term monitoring sites and metal deposition directly associated with Space Shuttle launch activity at two Launch Complexes (LC39A and LC39B). A secondary study examined metal concentrations at additional sites and increased the amount of elements measured to 48 elements. Our examination places a heavy focus on those metals commonly associated with launch operations (e.g., Al, Fe, Mn, and Zn), but a brief discussion of other metals (As, Cu, Mo, Ni, and Pb) is also included. While no observable accumulation of metals occurred during the time period of the study, the data obtained postlaunch demonstrated a dramatic increase for Al, Fe, Mn, and Zn. Comparing overall trends between the primary and secondary baseline surface water concentrations, elevated concentrations were generally observed at sampling stations located near the launch complexes and from sites isolated from major water systems. While there could be several natural and anthropogenic sources for metal deposition at KSC, the data in this report indicate that shuttle launch events are a significant source.

Concentrations of trace elements in American alligators (Alligator mississippiensis) from Florida, USA

Concentrations of 28 trace elements (Li, Mg, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Mo, Ag, Cd, In, Sn, Sb, Cs, Tl, Hg, Pb, and Bi) in the livers of juvenile and adult American alligators inhabiting two central Florida lakes, Lake Apopka (LA), and Lake Woodruff National Wildlife Refuge (LW) and one lagoon population located in Merritt Island National Wildlife Refuge (MINWR; NASA), were determined. In juveniles from MINWR, concentrations of nine elements (Li, Fe, Ni, Sr, In, Sb, Hg, Pb and Bi) were significantly higher, whereas six elements (V, Fe, As, Sr, Hg and Bi) were elevated in adults (p<0.05) obtained from MINWR. Significant enrichment of some trace elements in adults, relative to juveniles, was observed at all three sampling areas. Specifically, Fe, Pb and Hg were significantly elevated in adults when compared to juveniles, suggesting age-dependent accumulation of these elements. Further, As, Se and Sn showed the same trend but only in animals collected from MINWR. Mean Fe concentrations in the livers of adults from LA, LW and MINWR were 1770μgg−1 DW, 3690μgg−1 DW and 5250μgg−1 DW, respectively. More than half of the adult specimens from LW and MINWR exhibited elevated hepatic Fe concentrations that exceed the threshold value for toxic effects in donkey, red deer and human. These results prompted us to express our concern on possible exposure and health effects in American alligators by some trace elements derived from NASA activities.

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.

A Markov Decision Process for Managing Habitat for Florida Scrub-Jays

Abstract Florida scrub-jays Aphelocoma coerulescens are listed as threatened under the Endangered Species Act due to loss and degradation of scrub habitat. This study concerned the development of an optimal strategy for the restoration and management of scrub habitat at Merritt Island National Wildlife Refuge, which contains one of the few remaining large populations of scrub-jays in Florida. There are documented differences in the reproductive and survival rates of scrub-jays among discrete classes of scrub height (&amp;lt;120 cm or “short”; 120–170 cm or “optimal”; &amp;gt;170 cm or “tall”; and a combination of tall and optimal or “mixed”), and our objective was to calculate a state-dependent management strategy that would maximize the long-term growth rate of the resident scrub-jay population. We used aerial imagery with multistate Markov models to estimate annual transition probabilities among the four scrub-height classes under three possible management actions: scrub restoration (mechanical cutting followed by burning), a prescribed burn, or no intervention. A strategy prescribing the optimal management action for management units exhibiting different proportions of scrub-height classes was derived using dynamic programming. Scrub restoration was the optimal management action only in units dominated by mixed and tall scrub, and burning tended to be the optimal action for intermediate levels of short scrub. The optimal action was to do nothing when the amount of short scrub was greater than 30%, because short scrub mostly transitions to optimal height scrub (i.e., that state with the highest demographic success of scrub-jays) in the absence of intervention. Monte Carlo simulation of the optimal policy suggested that some form of management would be required every year. We note, however, that estimates of scrub-height transition probabilities were subject to several sources of uncertainty, and so we explored the management implications of alternative sets of transition probabilities. Generally, our analysis demonstrated the difficulty of managing for a species that requires midsuccessional habitat, and suggests that innovative management tools may be needed to help ensure the persistence of scrub-jays at Merritt Island National Wildlife Refuge. The development of a tailored monitoring program as a component of adaptive management could help reduce uncertainty about controlled and uncontrolled variation in transition probabilities of scrub-height and thus lead to improved decision making.

Seasonal variation in plasma thyroid hormone concentrations in coastal versus inland populations of juvenile American alligators ( Alligator mississippiensis): Influence of plasma iodide concentrations

Thyroid hormones, essential for normal growth and health, are associated with changes in temperature, photoperiod, and reproduction. Iodide, a necessary element for thyroid hormone production, varies in diet, and is more abundant in estuarine environments, which could alter thyroid hormone variation. However, associations between thyroid hormone concentrations in animals from marine versus freshwater environments, which could become more pertinent with rising sea levels associated with global climate change, are not well studied. To determine the importance of dietary iodide in seasonal variation of plasma thyroid hormone concentrations, we analyzed seasonal variation of plasma thyroxine ( T 4) and triiodothyronine ( T 3) concentrations in juvenile alligators from an estuarine habitat (Merritt Island National Wildlife Refuge; MI) and a freshwater habitat (Lake Woodruff National Wildlife Refuge; LW) and compared these results to plasma inorganic iodide (PII) concentrations. Alligators from MI did not display seasonal variation in plasma T 4, but exhibited a seasonal pattern in plasma T 3 concentrations similar to alligators from LW. Plasma thyroid hormone concentrations were consistently higher at MI than at LW. PII concentrations were correlated with plasma T 4 and T 3 concentrations in juvenile alligators from LW but not MI. The data on plasma T 4 and T 3 concentrations suggest altered iodide metabolism in estuarine alligators. Differences in thyroid hormone concentrations between the populations could be due to differences in dietary iodide, which need to be further evaluated.

Seasonal Androgen Cycles in Adult Male American Alligators (Alligator mississippiensis) from a Barrier Island Population1

The seasonal patterns of two primary plasma androgens, testosterone (T) and dehydroepiandrosterone (DHEA), were assessed in adult male alligators from the Merritt Island National Wildlife Refuge, a unique barrier island environment and home to the Kennedy Space Center in Florida. Samples were collected monthly from 2008 to 2009, with additional samples collected at more random intervals in 2007 and 2010. Plasma T concentrations peaked in April, coincident with breeding and courtship, and declined rapidly throughout the summer. Seasonal plasma T patterns in smaller though reproductively active adult males differed from those in their larger counterparts during the breeding season. Both size classes showed significant increases in plasma T concentration from February to March, at the beginning of the breeding season. However, smaller adults did not experience the peak in plasma T concentrations in April that were observed in larger adults, and their concentrations were significantly lower than those of larger males for the remainder of the breeding season. Plasma DHEA concentrations peaked in May and were significantly reduced by June. This is the first study to demonstrate the presence of DHEA in a crocodilian, and the high plasma DHEA concentrations that paralleled the animals' reproductive activity suggest a reproductive and/or behavioral role in adult male alligators. Similar to androgen variations in some birds, plasma DHEA concentrations in the alligators were considerably higher than T concentrations during the nonbreeding season, suggesting a potential role in maintaining nonbreeding seasonal aggression.

Determinants of Nest Survival in a Managed Florida Scrub-Jay Population

Abstract. Bird populations occupying managed transitional habitats often have low nest success because optimal habitat conditions are not maintained. In such cases, quantifying determinants of nest survival provides information for habitat maintenance or restoration. Our goal was to determine the current factors affecting nest survival in a managed but declining population of the Florida Scrub-Jay (Aphelocoma coerulescens) in Merritt Island National Wildlife Refuge. We used an information-theoretic approach and nest-survival models in program MARK to test a priori hypotheses for survival of Florida Scrub-Jay nests. Failure of Florida Scrub-Jay nests was common; only 35% of 614 were successful in producing at least one fledgling. Ninety-four percent of 399 nest failures were due to predation. Nest survival was highest in oak-dominated territories, varied by population center, and decreased with proximity to forest edges, as the season progressed, and with increasing accumulated rainfall prior to the nestin...