Nesting ecology, current status, and conservation of sea turtles on an uninhabited beach in Florida, USA

Although nesting beaches are critical resources for sea turtles, most beaches in the United States are disturbed by human influence, including human access, artificial lighting, and habitat alteration. In contrast, very few undisturbed beaches remain along the Atlantic coast, and these areas represent unique habitats that can help decipher the impacts of development on various species. We monitored nesting patterns and hatching success of three sea turtle species (Caretta caretta, Chelonia mydas, and Dermochelys coriacea) from 1985 to 2003 on Canaveral National Seashore, an uninhabited 38.3 km stretch of beach in Florida. We monitored the number of nests deposited annually, hatching success, predation rates, and spatial nesting patterns. Clutch sizes varied within, but not among years, most likely due to variation in size of nesting females rather than climate change or resource availability. The number of nests increased over the study period for all three species, indicating growing populations. Higher numbers of nests were deposited on the southern end of our beach than on the northern end. Hatching success did not vary by species, but was dependent on nest-protection effort, which increased during the study period. Protecting more nests with wire screens resulted in lower predation rates. We did not find any evidence suggesting that predators are using nest markers to locate eggs, even after using the same method of marking nests for 19 years. Our conservation efforts have lowered predation levels through increased screening effort, and over time the number of nests laid increased for each species. Collecting baseline data on nesting patterns in undisturbed locations will allow comparisons to be made on nesting trends and patterns at geographically close, but disturbed, localities.     

Sex ratio bias in hatchling sea turtles from artificially incubated eggs

Artificial incubation of eggs of green sea turtles, Chelonia mydas, above ground in styrofoam boxes results in a 23% drop in the number of hatchlings with ovaries, compared with samples from clutches left on the beach in natural conditions. This masculinization is consistent with the well-known effects of temperature on sexual differentiation in chelonians and with measurements showing that the styrofoam boxes were 1–1·5°C cooler than the sand on the beach at the depth of turtle nests. These findings verify previous suspicions about the use of styrofoam boxes in management programmes for sea turtles, and have implications for the conservation and husbandry of reptiles in general.     

Breeding success of hawksbill turtles Eretmochelys imbricata at Cousin island,seychelles and the implications for their conservation

The Cousin Island population of hawksbill turtles Eretmochelys imbricata has been studied for ten years. Each season new (untagged) and return (tagged) turtles are seen on the beaches; having once nested successfully these females are apparently faithful to the island.Most of the females breeding in the 1981–1982 and 1982–1983 seasons were intercepted and 144 nests were followed through to the emergence of young. Egg losses were mainly attributable to crab predation.Individual females laid up to six times (mean 3·1 times) in a season; clutch size and hatchling weight declined significantly in their later nests. Hatching and emergence success were high, especially in early nests; late in the season proportionally more developed embryos died.It is suggested that the completion of early, more successful and more productive nests could be safeguarded by delaying the start of the turtle hunting season.     

Managing predation on ground-nesting birds: The effectiveness of nest exclosures

Ground-nesting birds have declined world-wide, probably partly due to high nest predation. A non-lethal method for decreasing predation uses protective cages at nests. Tests have mainly looked at the effect of such nest exclosures on hatching success and adult predation, but several additional aspects need to be explored for a comprehensive evaluation of this conservation technique. Here, we test the effect of nest exclosures in two common European shorebirds: northern lapwing (Vanellus vanellus) and redshank (Tringa totanus), measuring hatching success, incubation length, hatching synchrony, hatchability, partial clutch loss, chick condition, and adult predation. In both species, protected nests had higher hatching success than unprotected nests. Taking into account incubation time, nest abandonment, hatchability and partial clutch loss, protected nests still hatched more young than unprotected controls. In lapwings, but not in redshanks, protected nests were incubated longer, but this did not impair the condition of lapwing chicks. Protected redshanks suffered increased predation on incubating adults, which often sit on the nest until a predator is close by. Our results emphasize the need for caution in the use of nest exclosures, particularly in redshanks and other species with similar incubation behaviour. Exclosures can, however, be a useful management tool in shorebirds that leave their nest early, when an approaching predator is still far away.     

Effects of landscape change on clutches of Phyllomedusa tarsius, a neotropical treefrog

Phyllomedusa tarsius is an arboreal frog species that suspends its eggs on leaves above water in order to achieve the high relative humidity necessary for embryo development. I compared the hatching success of P. tarsius in ponds located in pasture, Vismia spp. regrowth, Cecropia spp. regrowth, forest fragments and continuous forest at a site in central Amazônia. Reproductive success of P. tarsius is measured as percentage of clutches producing at least one tadpole and number of tadpoles produced per clutch. Reproductive success was higher in Cecropia regrowth, forest fragments and continuous forest, compared to pasture and Vismia regrowth. Desiccation and flooding were the main causes of clutch loss in pasture and Vismia regrowth, while predation was more frequent in forest and Cecropia regrowth. The levels of successful of P. tarsius clutches observed across all habitat types suggests that a landscape mosaic including pasture, secondary growth and forest fragments may allow for recolonization and genetic exchange to occur in isolated forest patches.     

Low reproductive success of leatherback turtles, Dermochelys coriacea, is due to high embryonic mortality

We examined the mechanism responsible for low reproductive success in leatherback turtles (Dermochelys coriacea) at Playa Grande, Costa Rica: low egg fertilization versus high rates of embryonic death. Leatherbacks at this beach had a high rate of fertility (=93.3%±2.5%, n=819). We incubated 10 eggs from every clutch encountered of 19 females during 3 months of the 1998-1999 nesting season. Fertility rate of some females decreased during the nesting season, but overall was high. Detection of fertility was difficult using standard methods because fertility rates cannot be determined accurately from nests excavated after hatching because of egg decomposition. Removal and incubation of eggs from nests provided a better estimate. Embryonic death, particularly in the beginning of incubation before embryos are visible to the unaided eye, was the cause of low hatching success in this population. Hatching success increased with increasing fertility and differed between females, with some mothers having 71-81% success and others 23-32%. Embryonic death and not low egg fertility drives poor recruitment at Playa Grande. Improved conservation of this species at Playa Grande will require a better understanding of the mechanism behind embryonic death.     

Signage reduces the impact of human disturbance on little tern nesting success in Portugal

This study evaluated the influence of human disturbance in nesting success of little tern (Sterna albifrons) and its interaction with the intrinsic seasonal variation in the birds’ breeding biology. During 2003-2005 we studied little tern nesting ecology in southern Portugal in two different types of habitat: their natural habitat (sandy beaches) and a man-made habitat (salinas). In both habitat types, annual variations were found in the distribution of nest initiation over the breeding season and in the size of the clutches. The percentage of nests producing hatched chicks varied between 26.7% and 66.4% in different years and habitats. The main causes of hatching failure varied between years and habitats, but predation, flooding and human activities were very common. No consistent differences in breeding parameters or nesting success were found between habitats. On sandy beaches, the effect of protective measures (warning signs and wardening) on nesting success, together with differences between years and within each breeding season, were assessed using a logistic regression model. The presence/absence of protective measures was the most important predictor of nesting success, with birds being up to 34 times more likely to succeed with protective measures. Seasonal declines were found for clutch size and egg volume, and season was also an important predictor of nesting success, with nests more likely to succeed earlier in the season. Hence, earlier breeders will be those that benefit more from protective measures, suggesting that conservation efforts for little tern can be maximised if concentrated earlier in the season.     

Estimates of sea turtle mortality from poaching and bycatch in Bahía Magdalena, Baja California Sur, Mexico

Bahia Magdalena on the Pacific coast of Baja California Sur, Mexico, is an important feeding and nursery ground for black turtles Chelonia mydas, loggerhead turtles Caretta caretta, olive ridley turtles Lepidochelys olivacea, and hawksbill turtles Eretmochelys imbricata. Despite international and national protection, sea turtles continue to be caught incidentally and hunted for consumption in large numbers. This study examines the mortality of sea turtles in Bahia Magdalena, focusing on (1) species distribution and number of carcasses found, (2) causes of death, (3) size frequency distribution and % juveniles in the catch, and (4) changes in average size over the past years. A total of 1945 turtle carcasses were found from April 2000 to July 2003 along beaches and in towns of the region with loggerhead (44.1%) and black turtles (36.9%) being the dominant species. Slaughter for human consumption was the primary cause of death of carcasses found in towns (95-100%), while carcasses on beaches mostly died of unknown causes (76-100%). Circumstantial evidence suggests however, that incidental bycatch was the main mortality cause on beaches. Black turtles suffered the highest consumption mortality overall (91%), followed by olive ridley (84%), hawksbill (83%) and loggerhead turtles (63%). Over 90% of all turtles found were juveniles or subadults. Carapace length of black turtles declined consistently over the sampling period, while that of loggerhead turtles increased. Our results strongly suggest that turtles are being taken at high and unsustainable rates; this may partially explain why the populations have not recovered despite widespread protection on nesting beaches.     

Effectiveness of different conservation measures for loggerhead sea turtle (Caretta caretta) nests at Zakynthos Island, Greece

In this paper, we evaluate the effectiveness of different well-tested conservation techniques in an effort to successfully protect sea turtle nests. From an eight-year study on the island of Zakynthos, West Greece, we have experimentally investigated the effectiveness of two different conservation techniques applied to loggerhead sea turtle nests and provided statistical measures to evaluate their conservation value. The categories of nests evaluated include: (i) nests incubated in situ, (ii) translocated into a beach hatchery, or (iii) protected by metal cages. Results of the analysis showed significant interannual variations in hatching success as obtained for each one of the three groups of nests. Significant differences were also observed when comparing hatching success data among the three groups of nests during the eight-year period. Overall, our results indicate that relocation of nests laid at highly threatened locations and the placement of protective cages on nests in situ provide adequate conservation measures that could allow an increase in hatchling production; although their choice and application should be based on the specific conditions and threats of each nest.     

Life history traits and food supplementation affect productivity in a translocated population of the endangered Hihi (Stitchbird, Notiomystis cincta)

We studied the effect of food supplementation, female age and clutch order on productivity in a translocated species. Food supplementation increased clutch size from 3.9 to 4.4 (average) eggs per nesting attempt, and more than doubled fledging and recruitment success. Supplemented females started a second clutch 9 days sooner after fledging first clutch chicks than unfed females. During second clutches, supplemented females incubated the eggs for a shorter period of time (15.2 days vs. 16.8). Older females laid larger clutches (4.6 vs. 3.7 eggs) than yearlings and incubated second clutch eggs for a shorter period (15.4 vs. 16.6 days). Females laid more eggs in first clutches (4.2 vs. 3.8 eggs), and those eggs took approximately 30% longer to lay than eggs in second clutches. The successful maintenance of hihi populations on the available islands may be dependent on the permanent provision of supplemental food at nest sites.     

The effects of heat stress, predation risk and parental investment on Malaysian plover nest return times following a human disturbance

Waders leave nests and conduct distractive displays when approached by people. The time taken for waders to return to nests depends on numerous factors that affect the costs and benefits of incubation and anti-predator behavior. Understanding this trade-off may help assess the reproductive consequences of different nest return times and identify variables to consider in breeding disturbance studies. We subjected 73 Malaysian plover (Charadrius peronii) nests to standardized human disturbances and an analysis of covariance was used to determine how weather, time of day, embryonic age, weeks into breeding season and nest attendance (proportion of time adults incubated nests) influence nest return times. Egg temperatures were estimated using a regression model that predicted the temperature inside unshaded eggs from air temperature, cloud cover and time of day (r² = 0.88). We assessed the relationship between nest return times and hatch success. Plovers returned to nests faster at higher modeled egg temperature (P = 0.010), in the morning (P = 0.003), if they had younger clutches (P = 0.038), and if they had high nest attendance prior to the disturbance (P = 0.015). Pairs that returned to nests faster had lower hatch success (P = 0.021). This may be because pairs that spend more time distracting humans may also do so for predators. These results suggest that short nest return times may not indicate low fitness costs of disturbance. The thermal and predation environment in addition to nest return times should be taken into account when assessing the deleterious effects of human disturbance.     

High levels of hatching failure in an insular population of the South Island robin: a consequence of food limitation?

Endangered birds in insular environments like New Zealand are often translocated to predator-free offshore islands for conservation purposes. Some translocated populations however exhibit reduced fecundity, and it has been suggested that either inbreeding (due to small number of founders) or resource shortages (due to high population density) may limit reproductive success. For example, the South Island robin (Petroica a. australis) population on Motuara Island (59 ha) was founded by only five birds but has increased to ∼600 individuals, or a density >10 times that of the mainland. Despite this apparent success, the rate of hatching failure in this population is three times higher than in mainland populations, with more than a third of eggs failing to hatch. To test if elevated hatching failure is the result of food limitation, we carried out a food supplementation experiment by providing females with mealworms equivalent to ∼50% of their daily energy requirements. Food supplementation had no effect on hatching success, clutch size, incubation attentiveness or nest size. Egg volume increased with food supplementation in one of the two years of this study, but both egg volume and incubation attentiveness were unrelated to rate of hatching failure. As previous genetic analyses confirmed that the bottlenecked population of robins on Motuara Island have significantly less genetic variation than their source population, we conclude that inbreeding depression, and not food limitation, is the most likely explanation for their high rate of hatching failure. We suggest that the experimental translocation of genetically dissimilar individuals be considered as a possible remedy for low productivity in island populations that were initiated with few founders.     

A review of sea turtle nesting activity along the Mediterranean coast of Turkey

Many parts of the Turkish coastline are important nesting grounds for sea turtles. The aim of this study was to assess the present state of sea turtle populations along the coastline of Turkey, by evaluating research conducted at various nesting grounds from 1979 to 2000. The results of the evaluation indicate that the Turkish coastline is the most important nesting area for Chelonia mydas, and the third most important nesting area for Caretta caretta after Greece and Libya (if nesting estimates for Libya are correct) in the entire Mediterranean. The most important C. caretta nesting beaches in Turkey are Dalyan (11.9%), Kumluca (11.3%), Belek (27.9%), Kizilot, (8.9%) and Anamur (8.8%), while those for C. mydas are Kazanli (24.1%) and Akyatan (54.4%). These sites are classified as “Nesting Areas of 1st Degree Importance”. Annual mean nest numbers along the coastline of Turkey are estimated to be ca. 2000 for C. caretta and 650 for C. mydas. Assuming that each adult female sea turtle nests three times per season, the annual numbers of nesting females along the beaches of Turkey range between about 500 and 800 for C. caretta and 130 and 300 for C. mydas. Annual nesting densities along the 204 km beach strip, which includes 17 important nesting grounds in Turkey, were 11.3 nests/km for C. caretta and 19.2 nests/km for C. mydas.     

Conservation and the scarecrow effect: Can human activity benefit threatened species by displacing predators?

Most wild animals show direct negative responses to human disturbance; however, disturbance may also have positive indirect effects by altering species interactions. In the Caribbean, introduced mongooses (Herpestes javanicus) are an important diurnal predator of the nests of critically endangered hawksbill sea turtles (Eretmochelys imbricata). We asked whether daytime visitor activity could benefit hawksbills by reducing mongoose activity in nesting habitat. We used track monitoring sites to measure how mongooses alter their space use in response to fluctuating human beach use and availability of hawksbill nests, and we estimated the indirect impact of human disturbance on nest predation for 5 years of hawksbill nesting. Human activity substantially decreased mongoose use of nesting habitat. Mongoose activity increased with abundance of nests and was lower at the edge than the interior of patches of beach vegetation, but neither factor altered relative sensitivity to disturbance. We estimated that, in addition to deterring mongooses from accessing nests on the open beach, human activity has the potential to reduce predation of nests in vegetation by up to 56% at our site, with the greatest per capita impact at low (<50) visitor numbers. Many forms of human activity negatively affect sea turtles, but our study indicates that there are positive aspects of daytime use of nesting beaches. Optimizing the trade-off between positive and negative impacts of disturbance could provide a useful approach for regulating tourist activity in critical habitat for threatened species.     

Effects of the introduced parasite Philornis downsi on nestling growth and mortality in the medium ground finch (Geospiza fortis)

Invasive species have the potential to detrimentally affect native ecosystems by out competing or directly preying upon native organisms, and have been implicated in the extinction of endemic populations. One potentially devastating introduced species in the Galápagos Islands is the parasitic fly Philornis downsi. As larvae, P. downsi parasitize nestling birds and have been associated with high nestling mortality and reduced growth rates. Here I document nestling growth and mortality in a bimodal population of the medium ground finch, Geospiza fortis. Observations were conducted over three years, and under variable ecological conditions. Annual parasite prevalence in nests ranged from 64% to 98%, and nestling mortality in nests with parasites ranged from 16% to 37%. Parasite load and parasite load per nestling follow a skewed distribution with many nests having relatively few parasites, and few nest having many. Parasite load, however, was not correlated with onset of breeding, clutch size, the number of nestlings, nestling survival or fledgling success. Parasite load per nestling, on the other hand, was correlated with clutch initiation date and the proportion of nestlings that died in parasitized nests. Neither nestling size nor growth rate differed between parasitized and unparasitized nests. In addition, male and female beak morphology was not correlated with parasite load, breeding variables or nestling survival. Thus, while overall mortality due to parasitism is high, ecological conditions and possible host defenses may potentially counter some of the detrimental affects of P. downsi on nestling size and growth. These results taken together suggest that parasitism of P. downsi larvae on nestling G. fortis has the potential to lead to large population declines.     

Long-term conservation efforts contribute to positive green turtle Chelonia mydas nesting trend at Tortuguero, Costa Rica

Worldwide, green turtle Chelonia mydas populations have declined and the species is classified as globally endangered. Tortuguero, Costa Rica, hosts the largest remaining green turtle rookery in the Atlantic basin. Tortuguero green turtles have been hunted since pre-Columbian times. Monitoring and conservation of the green turtle population began in 1955. The long-term efforts provide an excellent opportunity to evaluate the success of sea turtle conservation action and policies. Nest counts conducted 1971-2003 were analyzed to: (1) determine the nesting trend, (2) estimate rookery size and (3) identify events and policy decisions influencing the trend. A nonparametric regression model indicates a 417% increase in nesting over the study period. Rookery size was defined as the mean number of nests 1999-2003 and estimated at 104,411 nests year⁻¹, corresponding to 17,402-37,290 nesting females year⁻¹. A comparison with 34 index populations verifies Tortuguero as one of the two largest green turtle rookeries worldwide. Events and policy decisions in Costa Rica, Nicaragua, and Panama that comprise the main nesting, feeding and mating grounds for the Tortuguero population are likely to have had the greatest influence on green turtle survivorship. Conservation efforts and policies catalyzing increased hatchling production and decreased adult and juvenile mortality since 1963 have contributed to the positive nesting trend. The trend demonstrates that long-term conservation efforts can reverse nesting declines and offers hope that adequate management can result in recuperation of endangered sea turtle species.     

Breeding performance of the Indian sarus crane in the agricultural landscape of western India

The breeding performance of the Indian sarus crane Grus antigone antigone Linn. was studied in the agricultural landscape of western India during 1996-1998. Detailed records of 70 nests were maintained from egg laying till fledging. At least one chick hatched from 50 clutches (71.43%). Nineteen clutches (27.14%) were destroyed due to various factors, but at least 7 pairs re-nested. Egg mortality was mainly due to flooding (7.35%), predation (11.03%) and conflict with farmers (8.09%). Chick mortality due to predation was 8.24% and to unknown factors was 30%. Number of chicks hatched and number fledged did not differ significantly in different microhabitats. Average breeding success was 25.74%. Breeding success was comparatively lower in paddy crop fields than in other microhabitats due to human disturbance and higher predation risk. The juveniles formed only 10.14% of the total sarus sighted during the post-breeding period. An increasing conflict of sarus crane with the farmers in the agricultural landscape is a matter of concern for sarus crane conservation. The economic loss due to nesting in the crop field, if compensated, will help in sarus crane conservation.     

Conserving the terecay (Podocnemis unifilis, Testudines: Pelomedusidae) through a community-based sustainable harvest of its eggs

The exploitation of South American river turtles as a food source has long been considered the main factor contributing to the decline of populations. Along a stretch of the Aguarico River (Ecuador), we investigated the spatial and temporal distribution of terecay (Podocnemis unifilis) nests, factors affecting nest outcome, and the effect of offering a reward for each hatchling captured on the pattern of egg consumption by the local human community. Flooding influence on egg mortality appears to be particularly important in this Amazonian region, destroying 63.1% of all nests. This amount of nests resulted more than sufficient to satisfy the local community’s consumption needs (28.2%). The proposed reward for each hatchling ensured the voluntary participation of the Cofan people in the terecay conservation project, leading to: (i) nests being harvested only from sites where there were likely no hatching possibilities, (ii) efficient management and protection of nesting beaches with abolition of poaching of nests and adult females, and (iii) transplantation of nests from sites that would be flooded (and whose yield exceeds human consumption). Therefore, we argue that in this area of Aguarico River there are both biologically and socially favourable conditions for the establishment of a sustainable harvest of terecay eggs. Possible factors determining high nest mortality due to flooding in this area, as well as opportunities to make the project evolve toward economic self-sustainability, will also be discussed.     

Ecology and nest-site selection of leatherback turtles Dermochelys coriacea

Leatherback turtles Dermochelys coriacea often nest in places where their eggs are destroyed by high tides. Poor nest-site selection ranges from <2·5% in Malaysia to around 40% in the Guianas and appears to be related to beach topography. In the Guianas sparse tree lines and lagoons on the landward side of the nesting areas make sea-finding by the hatchlings more difficult if nests are dug too far away from the sea. It is suggested that, faced with the predicament of not nesting too near the water and not testing too far back from it, leatherbacks have adopted a scatter nesting strategy that ensures that at least some of their nests will be appropriately sited. Relocating poorly sited nests poses certain problems for conservation programmes.     

Sperm storage and low incidence of multiple paternity in the European pond turtle, Emys orbicularis: A secure but costly strategy?

The freshwater pond turtle, Emys orbicularis, has recently suffered from population declines throughout its range, mainly due to habitat destruction. The mating strategies of this species were studied using genetic data from successive clutches within and between years. To test for the occurrence and frequency of multiple paternity and sperm storage, genetic paternity at six microsatellite markers was assessed in 114 embryos and hatchlings from single and subsequent clutches of 11 females (including clutches from the same or consecutive years). Multiple paternity was rare and only found in two out of 20 clutches from 11 females. All annual successive clutches and 58% of the clutches in the next year, were fertilized with sperm from the same male. The use of stored sperm is thus a frequent strategy in E. orbicularis. However, hatching rate, hatchling mass, and hatchling length decreased in clutches fertilized by stored sperm, suggesting sperm depletion or deterioration through time. The occurrence of stored sperm despite an associated reduced reproductive output indicated that mating and/or the fertilization process is costly to females. The low incidence of multiple paternity may simply be the residual consequence of the capacity to store viable sperm. These results provide important and innovative insights for the conservation of E. orbicularis. In threatened populations, management strategies may aim to enhance effective copulations in order to increase the reproductive output of females.