Least tern disturbance observations and colony survey data

Coastal birds that rely on sandy beaches for breeding are vulnerable to catastrophic flooding events resulting from tropical cyclones. The effects of storm surge on annual productivity depend on the propensity and success of renesting attempts post-storm. From 2017-2021, I investigated the effects of storm surge on Least Tern (Sternula antillarum) annual productivity, renesting probability, and nest and chick survival after storms on Mississippi’s Gulf of Mexico Coast. Tropical cyclones made landfall during peak breeding period in three of these years, resulting in complete overwash of all colonies. Observers monitored daily nest survival, productivity (max fledge count/max nest count), and frequency of disturbance from avian predators at each colony. Total annual productivity (fledge count/ nest count across the study area) summed across colonies ranged from 0.00-0.07 in storm years and 0.29-0.66 in non-storm years. Probability of colony re-occupation declined as a function of storm date and increased with pre-storm nest success. Disturbance rate from avian predators did not increase post-storm compared to pre-storm periods. Nest survival increased with colony size and decreased in both late-season (non-storm) and post-storm time periods. Mean probability of chick survival was 0.20 ± 0.06 SD for peak nesting period in non-storm years, whereas mean predicted chick survival was 0.003 – 0.004 in storm years and in renesting periods in all years. Storm surge resulted in nearly complete loss of Least Tern breeding productivity despite renesting attempts and colony re-occupation after storms. I found no evidence that avian predation increased post-storm as a result of habitat changes; rather, similarly low productivity was observed for late-season breeding attempts in non-storm years. Repeated storm surge events could pose a serious threat to the viability of Mississippi’s coastal-nesting Least Tern population, and protection of Least Terns during early and peak nesting seasons is critical for ensuring breeding success.