The diving behavior of African clawless and spotted-necked otters in freshwater environments

Abstract

Understanding the diving behavior of semiaquatic mammals, particularly in relation to estimated aerobic dive limits and diet, is important to understand their adaptability and potential vulnerability to changes in prey type and distribution. The diving behavior of African clawless otters, Aonyx capensis, and spotted-necked otters, Hydrictis maculicollis, is poorly known, and no estimates of their dive performance in relation to targeted prey and calculated dive limits have been reported previously for freshwater environments. We investigated the diving behavior of both these otter species in freshwater environments within South Africa through video recordings of direct observations and subsequent video analyses where dive and recovery durations and dive function were recorded. African clawless otters were found to perform longer dives (mean ± SD = 26.9 ± 12.2 s), compared to spotted-necked otters (8.5 ± 7.6 s). African clawless otters showed substantial variation in dive durations, with the shortest dives sometimes lasting < 5 s, and the longest recorded dive being 70 s. The majority of spotted-necked otter dives lasted < 10 s, with the shortest recorded dive lasting 0.66 s and the longest recorded dive lasting 50.9 s. Spotted-necked otters performed different dive types that were evidently dependent on prey targeted, with dives targeting crabs (16.10 ± 1.91 s) being longer than dives targeting rainbow trout, Oncorhynchus mykiss (5.58 ± 0.17 s). The theoretical dive durations of African clawless otters were exceeded during play dives, while spotted-necked otters sometimes exceeded their theoretical dive durations when performing successful foraging dives. The results of this study suggest that spotted-necked otters can vary behavior in relation to prey and exceed theoretical dive duration during successful foraging dives to maximize the net rate of energy gain. Furthermore, when considering known individual-level dietary specialization and plasticity in these species, it may be predicted that dive behaviors are likely to vary substantially among individuals, and in relation to prey availability and localized habitat conditions.

Latrine site selection by African clawless otters, Aonyx capensis, and their behavior during latrine visitations

“…Observations recorded in this study confirm the findings by Jordaan et al (2017), where foot stomping behavior and ‘jiggle dance’ are associated with anal gland secretions and defecation. A common behavior recorded in otters at latrine sites is body rubbing, documented in the Giant Otter ( P. brasiliensis ; Leuchtenberger and Mourão 2009), the Neotropical Otter ( Lontra longicaudus ; Michalski et al, 2021), the North American River Otter ( L. canadensis ; Green et al 2015), the Spotted-necked Otter (Reed-Smith et al 2014), and the African Clawless Otter (Estes 1991; Jordaan et al 2017). Body rubbing is hypothesized to play a role in scent marking (Leuchtenberger and Mourão 2009; Green et al 2015).…”

Dive Performance and Aquatic Thermoregulation of the World’s Smallest Mammalian Diver, the American Water Shrew (Sorex palustris)

“…The mean dive time of this species is also slightly longer than predicted from allometry (cf., Fig. 4 of Jordaan et al 2021). That said, dive times in the 20-min dive trials were likely skewed towards shorter mean (but not maximum) durations than expected in nature.…”

“…In contrast, most dives in the wild by the smallest (~50 g) avian diver, the dipper (Cinclus mexicanus; <6 sec; Calder 1968), are shorter than for foraging water shrews, while the much larger 325-450 g bufflehead (Bucephala albeola) has a mean dive time of only 12.5 sec (Gauthier 1993). Even larger mink (Mustela vison; 850 g) and spotted necked otters (Hydrictis maculicollis; 4 kg) have comparable mean dive durations of 9.9 and 8.5 sec, respectively (Dunstone and O'Connor 1979;Jordaan et al 2021). Finally, only moderately longer average dive times are observed for juvenile (300-500 g) and adult muskrats (650-900 g) (19.2-22.0 sec; MacArthur et al 2001), and 1.5-2.0 kg free-ranging platypus, Ornithorhynchus anatinus (31.3 sec; Bethge et al 2003).…”

“…Given the significant physiological challenges facing small-bodied amphibious divers, it is surprising that relatively few studies have examined the diving capacity and aquatic thermal biology of mammals weighing less than 5 kg (e.g., Dawson and Fanning 1981; MacArthur 1984a; Evans et al 1994; Hindle et al 2006; Harrington et al 2012; Jordaan et al 2021). Moreover, to our knowledge, comparable data for the smallest mammalian divers (<100 g) are available only for star-nosed moles, Condylura cristata (McIntyre et al 2002), European water shrews, Neomys fodiens (Köhler 1991; Vogel 1998), and, to a more limited extent, American water shrews, Sorex palustris (Calder 1969; McIntyre 2000).…”

“…Given the significant physiological challenges facing small-bodied amphibious divers, it is surprising that relatively few studies have examined the diving capacity and aquatic thermal biology of mammals weighing less than 5 kg (e.g., Dawson and Fanning 1981;MacArthur 1984a;Evans et al 1994;Hindle et al 2006;Harrington et al 2012;Jordaan et al 2021).…”