Revisiting the behavioural framework of feeding in predatory aquatic mammals.

Abstract

Hocking et al . [1] (hereafter HEA) present a framework for defining and evaluating feeding strategies in predatory aquatic mammals. While we appreciate the review, we address three difficulties with the framework: (i) the tetrapod feeding cycle needs minimal revision to accommodate aquatic mammals, (ii) the proposed feeding strategies need further clarification and (iii) evolution should not be described as a logical sequence. Our goal is to clarify and expand on HEA's feeding framework to ensure that predatory aquatic mammals can be examined in a comparative framework with other tetrapods. First, HEA argue that the four stages of the tetrapod feeding cycle—ingestion, intraoral transport, processing and swallowing [2]—do not adequately address the problems faced by air-breathing aquatic mammals. HEA, therefore, propose an alternative feeding cycle: (I) prey capture, (IIa) prey manipulation and transport and (IIb) prey processing, (III) water removal and (IV) swallowing. These changes constrain our ability to compare feeding behaviour across tetrapod lineages. The tetrapod feeding cycle is already sufficiently flexible to accommodate behaviourally diverse clades, so we propose using the existing tetrapod feeding cycle [2] with some revisions based on HEA (figure 1). Figure 1. Modified feeding cycle of aquatic tetrapods based on Schwenk [2] and Hocking et al . [1]. (Online version in colour.) In the tetrapod feeding cycle, ingestion encompasses all behaviours used to capture, subdue, kill and process prey before it enters the oral cavity [2]. Therefore, HEA's stages I, IIa and IIb are already included in ingestion and can distinguish between different behaviours prior to prey entering the mouth (figure 1). For example, sea otters ( Enhydra lutris ) dive to grab benthic prey (prey capture), move prey using their mouth/forepaws (prey manipulation) and use tools/teeth to open hard-shelled prey (external prey processing) [3]. …