First evidence of recruitment in critically endangered Galpagos pink land iguanas (Conolophus marthae)

We present the first estimate of population dynamics parameters for critically endangered Galapagos pink land iguanas, Conolophus marthae, leveraging mark-recapture data collected between 2006 and 2021. Demographic parameters were estimated using the POPAN formulation of the Jolly-Seber model. This approach provided a solid and robust estimate, consolidating the results obtained from previous estimates based on the Lincoln-Petersen method evaluating only two sampling occasions. Our results suggest that the abundance of males was higher than that of females at each sampling occasion, probably due to differences in sex-specific behavior during the reproductive season. Our analyses also provide no evidence of a change in population size during the sampling period, estimated at 150-270 adult individuals, while suggesting positive entry rates. Finally, by comparing the biometric features of first-captured versus recaptured iguanas, we found that the former have more juvenile-like characteristics (i.e., they are, on average, smaller) than the latter. Although juvenile pink iguanas have rarely been recorded (only four sampled juvenile-like individuals in over 16 years of field work), our combined results provide the first clear indication that the only known C. marthae population actively recruits new members from younger age classes. Such recruitment may have prevented any measurable population decline in the last 16 years, but it was also not sufficient to clearly increase the population size. These results are of the utmost importance for the conservation of this species. They will guide future high-priority actions: (i) aiming at increasing population size by removing or mitigating threats and (ii) increasing the number of individuals by implementing a headstart program and/or founding a second viable population, as identified in the recently published IUCN Conservation and Management Plan.