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Across their worldwide distribution, bottlenose dolphins (Tursiops spp.) use a variety of techniques to detect, pursue, and capture prey. Dolphins may hunt independently or in groups, and specialized foraging behaviors have been identified at both the individual and population levels. These behaviors can involve tool use (Patterson & Mann, 2011), coordinated herding of prey (Engleby & Powell, 2019), benthic foraging techniques (Rossbach & Herzing, 1997), and even cooperative interactions with fishermen (Daura-Jorge et al., 2012). In many bay, sound, and estuary populations along the U.S. coast, dolphins have developed foraging strategies that incorporate local habitat features (Wells, 2019). For example, along the southeast coast of the U.S., strand-feeding dolphins utilize exposed mud and sand banks to drive prey onto shore (Hoese, 1971; Fox & Young, 2012). Other strategies are more specifically adapted to target and handle individual prey species. For instance, in the northern Gulf of Mexico, several dolphin populations have developed a technique to remove the spiny heads from catfish (Ariidae), consuming the remaining bodies (Ronje et al., 2017).
Following the Deepwater Horizon (DWH) oil spill in 2010, the Barataría Bay Estuarine System (BBES) Stock (Hayes et al., 2020) of common bottlenose dolphins (Tursiops truncatus; hereafter referred to as dolphins) became the focus of a long-term, multifaceted study. Over the course of this study, dolphins were observed engaging in a previously undescribed behavior, which we term drilling (or drill feeding), in which a single dolphin positions itself almost vertically in shallow water and thrashes its flukes/tailstock across the surface, presumably to forage for prey in the substrate below. Herein, we report on observations of this behavior and discuss its significance for the BBES Stock.
The Barataria Basin is a large estuarine-wetland system in southeastern Louisiana (USA), extending from Bayou Lafourche in the west to the Mississippi River in the east (Figure 1). The southern boundary consists of a series of barrier islands that separate the estuary from the Gulf of Mexico. The estuarine waters are turbid and shallow, with a mean depth of ~2 m and salinities that range from tidally influenced saline waters (~25%o) in the south to freshwater lakes (~0%) in the north (U.S. Environmental Protection Agency [U.S. EPA], 1999; Das et al., 2012). The substrate is soft and muddy, primarily composed...