Behavioural Response to Juvenile Distress Calls as a Measure of Extended Care in Crocodilians

Abstract

Crocodilians are among the last surviving members of the Archosauria clade, of which parental care is thought to be a shared trait (Coombs, 1989; Pough et al., 2001). The distress calls emitted by juvenile crocodilians play an integral role in recruiting this care. At present, most research into Archosauria behaviour and acoustic communication has been conducted on birds, whilst crocodilians have been relatively neglected. It has been reported that extended care in crocodilians is modulated by the size information encoded within juvenile distress calls (Chabert et al., 2015). The extent of this care and the effect that additional variables can have on behaviour has been largely ignored. Here we present evidence gleaned from playback experimentation using juvenile distress calls, that breeding period, socialness of breeding strategy, sex, species, relative body size and relatedness to the juvenile caller, can modulate crocodilian care. We propose that these variables are stronger determining factors of crocodilian response than the body size of a juvenile caller alone. This study sampled seven different species of crocodilian, four of which were categorised as Critically Endangered or Vulnerable. This is the first experimental study conducted into the extended care of male crocodilians and in the species Tomistoma schlegelii, Crocodylus siamensis, Osteolaemus tetraspis, Paleosuchus palpebrosus and Crocodylus rhombifer. We also provide the first scientific evidence of female nest guarding in T. schlegelii, a species that has been generally regarded as providing little or no parental care (Britton, 2009; Vitt & Caldwell, 2009). This study, and research like it, are arguably of importance as 47.8% of extant crocodilian species are either threatened or critically endangered (IUCN, 2019). More research into extended care within crocodilians could aid breeding programmes, both in the wild and captivity.

Date of Award	23 Jan 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Marc W Holderied (Supervisor) & Gareth Jones (Supervisor)