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.