Adaptive foraging strategy of an insular snake (Lycodon semicarinatus, Colubridae) feeding on patchily distributed nests of sea turtles

Foraging tactics of predators generally include two major modes, active searching and ambushing. A colubrid snake, Lycodon semicarinatus, is a typical example of a predator, which uses both tactics to forage on sea turtles on islands of the Kerama Group in the Central Ryukyu Archipelago, Japan. To investigate factors that determine the foraging mode of this snake, we conducted a four-year field survey on its foraging behaviour on sea turtles on another island, Okinawa Island. We found that the snake performs only active searching at our study site. Snakes visited a small area exactly above the nest of sea turtles and attempted to burrow a tunnel to feed on eggs and hatchlings in the sand. Tunnels leading from the surface of the beach to the inside of the nest were formed only by large snakes. Many other snakes used the already made tunnels to capture eggs and hatchlings in the nest. When the snakes caught a hatchling, they brought the hatchling away into the nearby bush area without swallowing it above the nest (taking-away behaviour). When snakes failed to find food on a nest, they terminated the intensive search above the nest in approximately 5 minutes irrespective of snake body size, season, and the condition of the nest. Subsequently, they left the nest and resumed extensive searching for other nests. Our findings showed that L. semicarinatus has a different foraging strategy depending on populations. Two environmental traits, diversity of available prey animals other than sea turtles and characteristics of sand that beaches consist of, were considered as factors that might cause the difference in the foraging strategy. The fine sand of our study site enables snakes to form a sturdy tunnel in nests. We presume that such an environment facilitates the use of active searching by the snakes to find the nest with tunnels suitable for exploitation. The taking-away behaviour may be effective to reduce excessive contact with other conspecifics under the situation that the nest with tunnels attracts many visitors. Furthermore, the observation that the snake left the nest site after a consistent duration of unprofitable searching supports the giving-up time rule, which has been predicted by a theoretical model concerning the optimal time for predators to leave a patch.

Not avian but mammalian scavengers efficiently consume carcasses under heavy snowfall conditions: a case from northern Japan

Interest in trophic interactions and ecosystem functions derived from carcass consumption by scavengers has been increasing. Here, we conducted the first evaluation of scavenging processes in an ecosystem with heavy snow, located in northern Japan, which is characterized by the limitations of visual and odor cues to detect carcasses. In this study, we verified the behavioral traits and assemblage compositions of avian and mammalian scavengers, which consumed six different carcass types buried in snow. We measured the visits of scavengers using camera traps between 2010 and 2020. The total scavenger richness observed was relatively low (only 12 species) compared to warmer biomes. We observed seven avian scavenger species, but their visit frequencies were extremely low compared with those of nocturnal mammalian scavengers, such as raccoon dogs (Nyctereutes procyonoides) and martens (Martes melampus), which were able to detect carcasses more rapidly and frequently. Our findings imply that large snow piles significantly prevent avian scavengers from detecting carcasses. In contrast, the snow piles could protect carcasses from the freezing air and ensure the occurrence of a basal level of microbial decomposition, possibly leading to carcass decomposition. This probably results in carcasses still providing odor cues for mammalian scavengers with heightened sense of smell. Moreover, considering the high carcass consumption rate (91.3% of full-body carcass; n = 23) and short carcass detection times (approximately 90 h) observed, it is possible that scavenging in heavy snowfall conditions has become systematically integrated into the foraging tactics of many mammalian scavengers.

Mere presence of co-eater automatically shifts foraging tactics toward ‘Fast and Easy' food in humans

Competition for food resources is widespread in nature. The foraging behaviour of social animals should thus be adapted to potential food competition. We conjectured that in the presence of co-foragers, animals would shift their tactics to forage more frequently for smaller food. Because smaller foods are more abundant in nature and allow faster consumption, such tactics should allow animals to consume food more securely against scrounging. We experimentally tested whether such a shift would be triggered automatically in human eating behaviour, even when there was no rivalry about food consumption. To prevent subjects from having rivalry, they were instructed to engage in a ‘taste test' in a laboratory, alone or in pairs. Even though the other subject was merely present and there was no real competition for food, subjects in pairs immediately exhibited a systematic behavioural shift to reaching for smaller food amounts more frequently, which was clearly distinct from their reaching patterns both when eating alone and when simply weighing the same food without eating any. These patterns suggest that behavioural shifts in the presence of others may be built-in tactics in humans (and possibly in other gregarious animals as well) to adapt to potential food competition in social foraging.

Intertidal foraging by gentoo penguins in a macroalgal raft

Foraging strategies in gentoo penguins (Pygoscelis papua) have been well studied (e.g. Croxall et al. 1988, Robinson & Hindell 1996, Lescroël et al. 2004, Takahashi et al. 2008, Xavier et al. 2017). The general consensus is this largest member of the three pygoscelid penguins displays both nearshore benthic and pelagic foraging tactics to consume combinations of crustaceans and fish. In a recent study, Carpenter-Kling et al. (2017) reported that gentoos at sub-Antarctic Marion Island displayed a novel foraging strategy that consisted of alternating typical lengthy foraging trips with much shorter nearshore afternoon trips. They suggest the latter foraging behaviour may be a response to suboptimal feeding conditions caused by local environmental change. This novel discovery reinforces the fact that, despite considerable study, not all foraging tactics in penguins have been documented. In this paper, we describe what we believe to be, yet another undocumented foraging tactic employed by gentoos.