Nesting ecology of the American crocodile in La Encrucijada Biosphere Reserve, Mexico

Abstract

Nesting of the American crocodile (Crocodylus acutus) is affected by natural and anthropogenic processes. In Mexico, few studies exist on reproductive traits of wild populations. We assessed the key reproductive characteristics ofC. acutusin the La Encrucijada biosphere reserve and the environmental and anthropogenic factors that influence them. From February to June 2014, we searched for nests in the reserve. Clutch incubation temperature was recorded by data loggers and climatic variables were obtained from La Encrucijada meteorological station. Additionally, outside the study area, net primary productivity was obtained for different sites in Mexico to relate it to clutch characteristics. We found 34 nests in nine nesting areas. Egg laying occurred in March, and hatching took place from mid-May to early June. Mean clutch and eggs characteristics are among the higher reported forC. acutus. Some egg attributes had a relationship with the net primary productivity. There was no relation between hatching success and external and internal characteristics of the nest. A high percentage of nests was poached (50%) mainly for egg consumption and fear of crocodiles, and the nests closer to the river, trees or human settlements are more likely to be poached.

Factors influencing the occurrence of negative interactions between people and crocodilians in Mexico

“…Five of the six negative interactions recorded occurred close to nesting sites (Table 2), where we observed 34 nests of C. acutus and 19 of C. crocodilus chiapasius in 2014 (Fig. 1; González-Desales et al, 2016a,b).…”

“…Since 2011, following the incidents with crocodiles, people living along El Hueyate estuary no longer engage in fish harpooning for fear of being attacked; they also destroy crocodile eggs (Sigler & Martínez-Ibarra, 1998; Sigler et al, 2000; González-Desales et al, 2016a) and no longer swim or bathe in the estuary. Negative human–crocodilian interactions affect both parties (Table 2; Pooley, 2015).…”

“…Monthly records of negative interactions with C. acutus in Mexico, with geographical coordinates, were compiled from CrocBITE (2018) for 15 August 1993–8 June 2018. From the coordinates we calculated the Euclidean distances to the nearest nesting site (Casas-Andreu, 2003; Cedillo-Leal et al, 2013; Cupul-Magaña et al, 2004; Valtierra-Azotla, 2007; Charruau et al, 2010; Sigler, 2010; Charruau et al, 2011; Hernández-Hurtado et al, 2011; González-Desales et al, 2016a; Charruau et al, 2017) and to the nearest site for which relative abundance data were available (Table 1), using ArcGis 10.2 (Esri, Redlands, USA). The distance of interactions to nesting sites and the distance of interactions to sites where abundance of C. acutus had been evaluated were classified in intervals, based on the Rule of Sturges (Sturges, 1926).…”

“…There are 64 human settlements and 26,992 inhabitants in the Reserve, of which 28.5% do not receive school education of any level; the main economic activities are fishing, agriculture and livestock breeding (INE-SEMARNAP, 1999). Reports indicate there are more crocodilians in the core zone than elsewhere (Sigler & Martínez-Ibarra, 1998; Peña, 2011) and nesting of both species has been recorded (Sigler & Martínez-Ibarra, 1998; González-Desales et al, 2016a,b), and therefore we examined human–crocodilian interactions and abundance of crocodilians only in the core zone.

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Crocodylus acutus (American crocodile) bite marks on a nest data logger

“…Previous studies have successfully deployed similar data loggers with built in sensors and data storage (López-Luna et al, 2015;González-Desales et al, 2016;Murray et al, 2016). However, these projects did not experience the same apparent level of instrument loss (Charruau, 2012).…”