Monitoramento de ninhos de tartarugas marinhas: uma análise da atração do predador por falsos ninhos

Abstract

Sea turtles make their nests on the beach and eggs are prone to predation by animals that forage on the coast. TAMAR has monitored nests in the Brazilian coast; especially in the Barreira do Inferno, municipality of Parnamirim, RN, where predation of nests by the fox (Cerdocyon thous) has been a considerable problem. In the 2015/2016 season, for example, most of the nests monitored were visited by foxes. Therefore, in this study we work with the hypothesis that the strategy of monitoring nests using marking stakes is causing the foxes to associate stakes with nests for predation. The hypothesis was tested through an experiment that involved the creation of fake turtle nests. During the period of May / June of 2017, during 5 nights an effort was made to construct false nests as follows: a trainee from TAMAR and a master's degree student in biological sciences went to the quadricycle beach simulating the encounter with a turtle and the posterior marking of the nest. In all cases we tried to reproduce a real encounter including the usual marking stake as well as the protection screen of the false nest. On the day after the experiment, a survey was carried out and it was observed that all of the false nests presented fox footprints in their environment. In later days it was observed even excavations of fox in the immediacy of the screen of protection of the false nests. A survey of footprints of foxes at random points on the beach without false or true nests estimated the visit frequency of foxes on the beach; in 10 random points drawn fox foxes were counted in 7 of them. In the next step, in May / June 2018, we included the analysis of different levels of intervention, such as digging holes without marking, as well as placing only stakes or screens without digging the sand. The experiments occurred after the reproductive seasons of 2017/2018. It was observed that the frequency of visitation of foxes in dug interventions was higher than the interventions with stake and little contact of the monitor with the soil, therefore this species can associate the presence of eggs with other type of stimulus without being only the visual the initial hypothesis suggested). It was concluded, then, that false nests are more visited than any random points on the beach (p = 0.0015). In addition, the three distinct interventions: stake only, digging or false complete nests were equally visited by the fox (p = 0.95).