Mammals as prey: Estimating ingestible size

Abstract

Most mammals have deformable bodies, making it difficult to measure the size of living or freshly killed ones accurately. Because small rodents are common prey of many snakes, and because nearly all snakes swallow their prey whole, we explored four methods for determining the ingestible size (the smallest cross-sectional area that the largest part of the rodent can be made into without breaking bones or dislocating joints) of 100 intact rodents, including 50 Musmusculus and 50 Rattus norvegicus. Cross-sectional areas derived from maximal height and width of specimens at rest or the same specimens wrapped snout to pelvic girdle are roughly 1.5× higher than areas calculated either by the height and width of the same specimens rolled into cylinders or by volumetric displacement. Rolling rodents into cylinders reduces cross-sectional area by straightening the vertebral column, lengthening the abdominal cavity, elevating the sternum, compressing the thoracic cavity, and protracting the shoulder joint, that is, changes similar to those seen in rodents eaten by snakes. Reduced major axis regression of the smallest attainable cross-sectional area, y, on mass, x, shows that y (in log mm(2) ) approximates 1.53x (in log grams)(0.69) for rats and 1.63x(0.64) for mice. Our results suggest that visual cues provided by live rodents might lead most predators, like snakes, to overestimate ingestible size and hence rarely attack prey too large to ingest.

A Model of the Anterior Esophagus in Snakes, with Functional and Developmental Implications

“…When snakes feed on prey with a relatively large cross-sectional area (Cundall and Deufel, 2006;Close and Cundall, 2012), the prey fills the oral cavity and the esophagus. To fill the oral cavity, the mandibles are depressed (Fig.…”

Heavy, Bulky, or Both: What Does “Large Prey” Mean to Snakes?

“…6a), or a combination of those variables, as well as structural components of predator gape (e.g., cranial bones, soft tissues; Fig. 3)—attributes difficult to measure for both prey and predators in ways that are functionally relevant, variable across taxa and methods, and controversial (e.g., King, 2002; Martins et al, 2002; Close and Cundall, 2012; Hampton and Moon, 2013; Hampton, 2018; Cundall, 2019; Moon et al 2019; Gripshover and Jayne, 2021; Cundall and Irish, 2022; Jayne et al, 2022). Nonetheless, qualitative comparisons and experimental studies indicate significant relationships between RPB and structural correlates of gape (e.g., Cundall and Greene, 2000:324; Close and Cundall, 2012; Gripshover and Jayne, 2021; Cundall and Irish, 2022; Jayne et al, 2022).…”

“…Bulk describes a key aspect of snake feeding and has been used in this sense (e.g., Marques et al, 2010; Passos et al, 2019:9; Barends and Maritz, 2022a; Solórzano and Sasa, 2022) and yet provides an umbrella for more precise terms and elaborations (e.g., Close and Cundall, 2012; Cundall, 2019; Moon et al, 2019; Gripshover and Jayne, 2021; Jayne et al, 2022); moreover, this overarching descriptor is useful in realms as different as functional morphology and public outreach (a child alerted us to the pillow example). High RPB implies high handling costs (more time and energy for ingestion and concomitant risks from other predators), separate from but interacting with those imposed by high RPM (King, 2002; see especially Close and Cundall, 2012; Jayne et al, 2022; Kornilev et al, 2022). Another core prediction of MBT is that snakes feeding on high RPB prey are specialized for enhanced gape regardless of RPM, whereas feeding frequencies depend on eating type III (high RPM, less often) versus IV prey (low RPM, more often).…”

“…In terms of prey ID and shape, earthworms, centipedes, and some chordates are elongate (type II); limbed squamates and mammals span fusiform to ovoid, and some amniote eggs are spherical (type III). Type IV prey vary in overall dimensions, density, and/or deformability relative to mass but are defined by a need for wide predator gape at lower RPM—note that fusiform or roundish prey can differ in density and/or deformability, such that a bird or a tortoise would yield lower RPM than a rodent with equivalent cross-sectional area (Close and Cundall, 2012; Jayne et al, 2022; see below). Thus, although high RPB is obvious for shad and many other fishes because of disparate major and minor cross-sectional axes (Fig.…”

Perils of ingesting harmful prey by advanced snakes

“…may consume anuran internal organs (Arroyo‐Trejos & Mora, 2016; Bringsøe et al ., 2020, 2021; Bringsøe & Holden, 2021), and species from the subfamilies Dipsadinae and Pareinae and genus Storeria pull snails from their shells (Rossman & Myer, 1990; Danaisawadi et al ., 2016; Arteaga et al ., 2018). However, the majority of snakes swallow their victims whole (see Cundall & Greene, 2000; Cundall, Tuttman & Close, 2014), and this behaviour sometimes constrains their diet (Close & Cundall, 2012). For many ophidians, predator and prey size are positively correlated, with larger snakes consuming larger prey and excluding small items; this may be especially pronounced for constrictors (Arnold, 1993; Cundall & Greene, 2000).…”