Large predators often play important roles in structuring marine communities. To understand the role that these predators play in ecosystems, it is crucial to have knowledge of their interactions and the degree to which their trophic roles are complementary or redundant among species. We used stable isotope analysis to examine the isotopic niche overlap of dolphins Tursiops cf. aduncus, large sharks (>1.5 m total length), and smaller elasmobranchs (sharks and batoids) in the relatively pristine seagrass community of Shark Bay, Australia. Dolphins and large sharks differed in their mean isotopic values for δ 13 C and δ 15 N, and each group occupied a relatively unique area in isotopic niche space. The standard ellipse areas (SEAc; based on bivariate standard deviations) of dolphins, large sharks, small sharks, and rays did not overlap. Tiger sharks Galeocerdo cuvier had the highest δ 15 N values, although the mean δ 13 C and δ 15 N values of pigeye sharks Carcharhinus amboinensis were similar. Other large sharks (e.g. sicklefin lemon sharks Negaprion acutidens and sandbar sharks Carcharhinus plumbeus) and dolphins appeared to feed at slightly lower trophic levels than tiger sharks. In this seagrass-dominated ecosystem, seagrassderived carbon appears to be more important for elasmobranchs than it is for dolphins. Habitat use patterns did not correlate well with the sources of productivity supporting diets, suggesting that habitat use patterns may not necessarily be reflective of the resource pools supporting a population and highlights the importance of detailed datasets on trophic interactions for elucidating the ecological roles of predators.

mukherjee, Shomen, jayanti ray-mukherjee, and robin Sarabia. 2013. Behaviour of American Crows (Corvus brachyrhynchos) when encountering an oncoming vehicle. the Canadian Field-naturalist 127(3): 229-233.A carrion feeder attempting to forage on a road benefits greatly from an appropriate response to vehicular traffic. in this observational study, we tested the ability of American Crows (Corvus brachyrhynchos) to judge the behaviour of fast-moving vehicles and avoid collision on a narrow road. unsurprisingly, American Crows feeding in the same lane as the approaching vehicle always flew off, but interestingly, a significant proportion of American Crows in the opposite lane chose to remain on the road. in addition, 21% of the American Crows in the same lane as the approaching vehicle walked over to the opposite lane to avoid injury, but none of the American Crows in the opposite lane walked over to the lane in which the vehicle was approaching. these are among the first quantitative data indicating that a non-human animal can detect the directionality of on coming vehicles on a road and, like humans, actively move out of the way or switch lanes to avoid death based on an understanding of the bahaviour of vehicular traffic.

No abstract

Bottlenose dolphins (Tursiops truncatus) are abundant in many coastal ecosystems, including the coastal Everglades. Understanding spatial and temporal variation in their abundance and group sizes is important for estimating their potential ecological importance and predicting how environmental changes (e.g. ecosystem restoration) might impact their populations. From August 2010 to June 2012, we completed a total of 67 belt transects covering a total of 2650 linear km and an area of 1232 km2. Dolphin densities varied spatially and temporally. The highest densities of dolphins were found in coastal oceans and inland bays and were lowest in rivers. Use of rivers, however, increased during the dry season while densities in other habitats remained similar across seasons. Dolphins appeared to prefer portions of bays close to mangrove-covered islands over open waters. A resighting rate of 63.6% of individuals across the 2-year study suggests that at least a portion of the population is probably resident within study regions over long time periods. The largest groups (mean 6.28, range 1–31) were found in open waters and bays despite apparently low predation pressure. Indeed, shark bite scars – likely the result of unsuccessful predation attempts – were conclusively observed on only 1% of individuals. Although further studies are warranted, the high densities of dolphins suggest that they are an important upper trophic level predator in the coastal Everglades, but their ecological importance probably varies in space and time.