When do endangered pygmy bluetongue lizards move and why should we care?
Animal species with different behaviors will require different conservation management. For instance, less mobile species will be easier to retain within defined conservation areas, but will be more likely to need assisted colonization to respond to climate change. The pygmy bluetongue lizard, Tiliqua adelaidensis, considered extinct for 40 years, was rediscovered in 1992. It is now known from a few isolated remnants of native grassland in a small region of South Australia, where it lives in single-entrance, vertical burrows constructed by lycosid and mygalomorph spiders. Lizards rarely move far from the burrow entrance, where they ambush passing invertebrate prey. Hazards from further movement include the risk of predation while exposed on the surface, and the risk of moving beyond the boundaries of their small habitat patches. Our question concerned the amount of movement among burrows, and how that affects management of a population.
We combined multiple sources of data to deduce patterns of movement. We included data from field observations, from video recordings over 23 burrows for 10 days each month, from pitfall trapping over two years, from genetic analyses using microsatellite DNA, and from experimental releases into artificial burrows (and video records of lizard behavioural responses).
We found that movements away from burrows were short and infrequent, and that those movements occurred more often early in the spring than later in the summer. Video records showed 25 of 48 monitored lizards remained in the same burrow for one, and sometimes two years. Pitfall trapping confirmed the most active time out of the burrow was the austral spring (October: 208 captures per 1000 trap nights, November: 42 captures, December: 4 captures, no adult captures in other months) and that 95% of all adult trap captures were males, probably seeking mating partners. At least 78% (of 38 litters) (mean of 3.23 live offspring/ litter) had multiple paternity, implying high promiscuity. When simulated translocations happened in early spring, over 80% of lizards moved away from their new burrows, but less than 10% moved in summer.
We imply that site management to reduce predators and discourage dispersal should be focused around spring, the time of maximum movements, and, if assisted colonization is considered as a management option, the best time to allow released lizards to adjust to a release site might be later in summer when natural movements are low.