Reptile and amphibian monitoring: Channel Islands National Park 2010–2015 annual report

Coonan, Timothy; Lee, Lena; Shaskey, Laura

doi:10.36967/nrr-2286638

In 2010–2015, staff at Channel Islands National Park monitored reptile and amphibian populations on three of the park’s five islands, using methods developed in the 1980s for the park’s long-term ecological monitoring program. Herpetofauna have been monitored regularly since 1993 by recording lizard and amphibian abundance on cover board transects located in areas of representative native habitat on Santa Barbara, Anacapa, and San Miguel Islands. We collect data on all five herpetofauna species that are present on these three islands. The methods return adequate abundance data for island night lizards (Xantusia riversiana), southern alligator lizards (Elgaria multicarinata), and Channel Islands slender salamanders (Batrochoseps pacificus), but do not pick up sufficient numbers of island fence lizards (Sceloporus occidentalis beckii) or side-blotched lizards (Uta stansburniana) to determine their status. In the park, island night lizards occur only on Santa Barbara Island, and in 2014 they were removed from the Federal list of endangered and threatened species. They are long-lived and occur at high densities. Our 20-year dataset indicates high recruitment of night lizards in the mid-1990s, after the end of a six-year drought, and then lower but apparently cyclic recruitment following that. The age structure is dominated by older individuals, which may have suffered some mortality in the droughts of 1986–1992 and 2011–2015. However, overall, night lizards have increased in abundance, and may generally be buffered from the effects of drought by their underground habits. Channel Islands slender salamander numbers also increased over time on San Miguel Island cover board transects, even throughout the current drought. Like night lizards, they may also be buffered from drought by their proclivity to remain underground unless sufficient precipitation has fallen. Alligator lizard abundance declined over time on all three San Miguel Island cover board transects and on two Anacapa Island transects. Unlike the other two species analyzed, alligator lizards are active mainly aboveground, and may be more susceptible to the effects of drought. For the two larger species (night lizards and alligator lizards), we assessed annual body condition, using the slope of the regression line of weight on snout-vent length cubed. The regression slope coefficient varied over time in night lizards, and the species also showed some cyclicity in recruitment. For alligator lizards on East Anacapa, the slope of the weight-length regression generally increased over time.

Reptile and amphibian monitoring: Channel Islands National Park 2010–2015 annual report

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