Nest placement and overwash risk of ground-nesting Black Skimmers and Sooty Terns on the Texas coast

There were 256,048 colonial waterbirds nesting on roughly 300 islands on the TX coast in 2024. Six of these species (Sooty Tern, Onychoprion fuscatus; Reddish Egret, Egretta rufescens; American White Pelican, Pelecanus erythrorhynchos; Black Skimmer, Rynchops niger; Least Tern, Sternula antillarum; American Oystercatcher, Haematopus palliatus) are ranked as Critically Imperiled or Imperiled on the state’s list of Species of Greatest Conservation Need. All but the Reddish Egret are ground-nesting birds.

Researchers monitoring waterbirds in Texas have observed that an important cause of nest failure for ground-nesting waterbirds is from islands being overwashed, a trend that has been amplified by colony islands shrinking at 3% per year. 

However, two tropical cyclones that impacted the Texas coast in 2024 showed that nest failure from overwash was not uniform across ground-nesting species. Rather, it was related to island elevation and fine-scale factors such as nest substrate, the elevation of nests within islands, and the stage of nesting at time of overwash.

Although nest counts of colonial waterbirds on islands have been conducted annually since 1973, there is no corresponding information collected on nest placement within islands, the microhabitat around nests, and where that habitat is located, precluding an understanding of the risk of nest failure for these species. 

If we have information on nest placement and an assessment of overwash risk, then we can provide science-based guidance on island design and rehabilitation to improve the nest success of these imperiled species.

Therefore, we propose to fill these knowledge gaps and determine the relative risk of nest overwash for two ground-nesting species for which there are existing nesting data: the critically imperiled Sooty Tern and imperiled Black Skimmer. 

Our objectives are to: (1) provide coastal resource management agencies with baseline data on nest elevation and microhabitat within islands, (2) calculate island-specific risk of nest overwash, and (3) coordinate and augment information for the ongoing colonial waterbird island rehabilitation effort in the Colony Island Network Design and Implementation (CINDI) project in support of science-based island rehabilitation decisions.

We will achieve our objectives by extracting nesting data from existing aerial images of colonies taken by a drone during the CINDI project, and by developing island-specific nest overwash probability models based on long-term water level observations and under different storm surge scenarios in the future.