Frank F. Rivera-Milán, G. Scott Boomer, Alexis J. Martínez
The Condor 118 (2), 300-308, (23 March 2016) https://doi.org/10.1650/CONDOR-15-110.1
KEYWORDS: Bayesian state-space model, distance sampling, monitoring, Patagioenas inornata wetmorei, P. leucocephala, population assessment
The Puerto Rican Plain Pigeon (Patagioenas inornata wetmorei) and the White-crowned Pigeon (P. leucocephala) are hunted illegally in Puerto Rico, despite being protected. Data are lacking to estimate how many are hunted illegally each year. For this reason, we used abundance estimates derived from distance sampling surveys conducted in 1986–2014 to (1) fit a Bayesian state-space model, (2) estimate posterior distributions for population and harvest management parameters (e.g., growth rate, carrying capacity, and maximum sustainable harvest rate), and (3) predict abundance in 2025 as a function of potential illegal hunting in 2015–2024. For the Plain Pigeon and White-crowned Pigeon, respectively, the intrinsic rate of population growth was 0.351 (95% credible interval = 0.086–0.737) and 0.352 (0.094–0.699), population carrying capacity was 55,840 (29,649–96,505) and 73,692 (47,225–98,434) individuals, maximum sustainable harvest rate was 0.176 (0.043–0.369 and 0.047–0.349), and predicted abundance was 20,536 (8,167–89,040) and 29,361 (1,779–100,937) individuals in 2025. Both pigeon populations increased from low numbers in the 1980–1990s, recovered quickly after hurricanes in 1989 and 1998, surpassed carrying capacity in 1995–2008, and decreased sharply at the same time that legal hunting of columbids increased in 2008–2014. Our monitoring and modeling results suggest that an increase in illegal hunting may be responsible for some of the abundance decline in 2008–2014, and that population sustainability may be affected by illegal hunting in 2015–2025. Therefore, data collection and the control of illegal hunting should be considered management priorities. Because we are updating model-based abundance predictions annually with monitoring data, we can inform management decisions, evaluate the results of conservation actions taken to maintain the pigeon populations fluctuating around carrying-capacity levels, and learn from the comparison of estimated and predicted abundances. Our monitoring and modeling scheme is applicable to other resident and migratory bird populations in the Caribbean.