The lattice FED had to be removed prior to hatchling emergence due to the inability of the hatchlings to emerge en masse through openings that were smaller than those in the standard and aluminium FEDs. Since their introduction in the season, the aluminium FEDs continue to be used occasionally when foxes appear to be showing a persistent interest in a nest, and occasionally to prevent nest compaction on beaches with high human traffic.
TurtleCare volunteers monitored nests continuously throughout the season. All disturbances, including predator impacts, hatchling emergence, and nesting success and failure data were recorded using the Queensland Turtle Conservation Project protocol [ 18 ]. We recorded the incidence of sea turtle nesting and fox depredation of sea turtle clutches for the 10 year period of the study. The nesting and emergence census in the study area was conducted each season from the date of the first nesting occurrence usually in November until the final natural nest emergence for the season usually in April.
Empty nests breached after emergence were noted Table 1 but were not treated as breached. If unsure whether breach occurred during or post emergence, the nest was recorded as breached. Due to the large area of potential nesting beach relative to the size of the volunteer base, monitoring was optimised by focusing on early morning track searches and evening turtle searches, particularly when females were expected to return to lay approximately 14 days after previous nesting.
Turtle nest depredation by foxes was recorded during the whole study, but other fox activity on beaches in the study area was not monitored prior to In September , an annual sand plot monitoring program was implemented to track fox activity. Ten sand plots were established at approximately 1 km intervals on beaches within the study area Fig 1 [ 19 ]. The 1.
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Surveys were conducted annually between and During each survey, sand plots were prepared each evening between and hrs, and then checked between and hrs the following morning for three consecutive days between August 30 and September 15 each year. All fox track incursions onto the sand plots were counted. A set of fox tracks heading in any direction across the sand plot was deemed an intrusion. Tracks are expressed as the number of track intrusions per sand plot per night.
To enable the plots to be raked out and checked within the one-hour timeframe each evening and morning, half of the plots were used simultaneously, with the second half being operated following a break of one or two nights. A total of 19 foxes were trapped and humanely euthanised by firearm during Period 1, and an unrecorded number of dens were fumigated.
One successful den fumigation i.
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Despite the formal cessation of lethal fox control in June , three foxes were removed from the study area in Period 2 for reasons unrelated to this study. A further 14 nests were untouched by foxes during incubation and emergence but were disturbed after successful nest emergence Table 1. This study documented reductions in fox depredation of turtle nests over a period of ten years, despite the cessation of lethal fox control after five years.
The observed reduction in the depredation of turtle nests in Period 2 was somewhat counter intuitive given that one might expect a higher level of clutch depredation in the period when no lethal fox control was undertaken. The Period 1 results showed that meshing played an important role in protecting nests from clutch depredation by foxes.
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Results for Period 2 appear to indicate that the reduced clutch depredation was not attributable to nest meshing. However, these results should be interpreted cautiously. All located turtle nests were covered with a standard FED as soon as possible after locating a nest. With the exception of and , the known number of nests going undetected and unmeshed was declining Table 1. Generally, since its humble beginnings in , the growth of the volunteer base has resulted in fewer nests going undetected and unmeshed in most seasons.
On occasion, this has required the use of a range of FED options to prevent clutch depredation. Given that the fox had successfully breached the FED and received some reward for its effort, it was expected that the fox would return the following night. As predicted, the fox returned on the night following the first depredation and attempted to breach the nest again. The stronger FED proved to be impenetrable and the nest remained intact. On the third night the fox again returned but did not attempt to dig.
No further attempted nest digging occurred at Buddina beach, despite the presence of fox tracks for the remainder of the season near all the Buddina nests. The use of the lattice FED was extended to other beaches as required in the season, and foxes did not breach any other nests that season on any beach in the study area. In this regard, the timely introduction of the impenetrable lattice FED may have contributed to foxes learning to ignore an interesting potential food odour that was consistently proving to be unobtainable.
Although the lattice FEDs are no longer used, their deployment in the season may have played an integral role in the observed changes in nest predation in subsequent seasons. Five egg chambers were unable to be located, which resulted in all five nests remaining unmeshed for the entire incubation period. No predation occurred on any of the nests despite the beach falling within the home range of a known and monitored fox family. In this instance, the five unmeshed nests functioned as unintended control nests. Despite the strength of the lattice FED, it is impractical for routine use due to the difficulty transporting it compared to the standard FED, which can be rolled and the requirement for its removal prior to nest emergence due to hatchling inability to pass through easily en masse.
The aluminium FED Fig 2 was also an available option where foxes appeared to be showing increased interest in a nest meshed with a standard FED. The aluminum FED also has the problem of being difficult to transport, but has the advantage that hatchlings can easily pass through during emergence, which enables it to be left in place up to and beyond hatchling emergence. Without fox density data, and with the fox activity index only commencing in , one cannot discount the possibility that the lethal fox control in Period 1 contributed to a reduction of the fox population in Period 2.
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Virtually all animals have the capacity to learn from experience, which enables them to modify their behaviour in response to situations they could not experience before birth [ 21 ]. Avital and Jablonka [ 22 ] note that the ability to learn allows animals to create new and discard old behaviour patterns in response to changing, but recurring, features in their environment.
Ultimately, learned behaviour enables an animal to use its physiological traits to maximise its fitness. In some instances it may be in response to an acute life or death situation, such as avoiding a predator, but learned experience is also likely to teach it where to best invest its energy for greatest reward. Also, like many other species, foxes are thought to be adept at teaching their young a range of life skills, including where and how to obtain food [ 5 , 23 ].
Thus, learned behavior in relation to which cues are likely to provide an energy benefit, and which are not, could be passed from parent to offspring. This may explain the cross-generational decline in nest depredation found in this study despite the consistent presence of a fox population. Such learned behavior and rationalisation of investment has been well documented in other species too.
Studies in Turkey and the USA have also documented the successful use of predator exclusion mesh and cages to reduce depredation of sea turtle nests by foxes [ 6 , 27 ]. Ratnaswamy et al [ 28 ] found that the meshing and caging of sea turtle nests more effectively reduced depredation by raccoons than lethal predator control.
Some studies, however, have demonstrated that exclosures may actually lead to increased predation [ 29 — 34 ], probably in most cases prompted by the visual stimulus of the potential prey inside the exclosure. For nest exclosures in the study area, the location of the FED below the surface of the sand eliminates, or greatly reduces, the opportunity for discovery through visual cues. The irregularity of nest emergence also makes it impractical for a predator to wait for a turtle nest emergence to access hatchlings. The fox is thought to use mainly olfactory cues, such as turtle body scent on turtle nesting crawls and egg odour to locate turtle nests [ 35 ] and some visual clues [ 34 ].
This may explain why foxes only occasionally dug under the outside edges of the mesh but more often persisted in the centre above the chamber where the odour was likely to be strongest. The success of nest exclosures elsewhere for other species has been variable. In Alaska, where predator exclosures were used to protect nesting western sandpipers Calidris mauri , successful exclusion of arctic foxes Vulpes lagopus decreased as the nesting season progressed [ 32 ].
The persistence of the arctic fox in that study may have been fueled by the additional visual stimulus of sandpipers inside the exclosure. An incubating turtle nest provides olfactory stimuli, and probably auditory stimuli in the few days prior to emergence, but no visual stimuli until the hatchlings emerge. The use of nest exclosures, or FEDs, as a primary conservation tool is not suitable for all locations. In many instances the use of predator exclosures may be impractical due to a range of factors, including cost, nesting density, or remoteness.
Meshing for predator control on that beach would require the use of more than 1, pieces of mesh spread across only 1. In such conditions, the mesh and pegs would become obstacles for nesting turtles and potential hazards for other beach users. There is a range of tools available to control foxes and mitigate their impacts on vulnerable native species. This study has shown that non-lethal fox management can increase hatching success in sea turtle clutches.