Responses of Australian wading birds to a novel toxic prey type, the invasive cane toad Rhinella marina

Abstract

The impact of invasive predators on native prey has attracted considerable scientific attention, whereas the reverse situation (invasive species being eaten by native predators) has been less frequently studied. Such interactions might affect invasion success; an invader that is readily consumed by native species may be less likely to flourish in its new range than one that is ignored by those taxa. Invasive cane toads (Rhinella marina) in Australia have fatally poisoned many native predators (e.g., marsupials, crocodiles, lizards) that attempt to ingest the toxic anurans, but birds are more resistant to toad toxins. We quantified prey preferences of four species of wading birds (Nankeen night heron, purple swamphen, pied heron, little egret) in the wild, by offering cane toads and alternative native prey items (total of 279 trays offered, 14 different combinations of prey types). All bird species tested preferred the native prey, avoiding both tadpole and metamorph cane toads. Avoidance of toads was strong enough to reduce foraging on native prey presented in combination with the toads, suggesting that the presence of cane toads could affect predator foraging tactics, and reduce the intensity of predation on native prey species found in association with toads.

Social transmission of avoidance among predators facilitates the spread of novel prey

“…For example, range expansion of predators or their prey can lead to populations that are naïve to prey defences. This often has disastrous consequences, but sometimes avoidance occurs much more rapidly than expected 47 . Variation in social behaviour and predators' propensity to learn by observing others could help explain why some species have been able to associate toxicity of novel prey rapidly and consequently avoid consuming them 48 .…”

The impact of invasive cane toads on native wildlife in southern Australia

“…Most Australian birds that prey on anurans can detect and tolerate the toad's toxin (Beckmann and Shine , ; Beckmann et al. ). Although one of the bird species we counted can be killed by ingesting toads (laughing kookaburra Dacelo novaeguineae : Covacevich and Archer ; but see Ringma ), this vulnerability has not translated to population‐level impacts.…”

“…Introduced from Hawaii to northeastern QLD in 1935, this highly toxic anuran has since invaded more than 1.2 million km 2 of tropical and subtropical Australia (Lever 2001;Urban et al 2007Urban et al , 2008 and has also spread into southeastern QLD and northeastern NSW (Seabrook 1993;Lever 2003). Cane toads were introduced to NSW between 1964 and 1966, when a satellite population was established in Byron Bay (van Beurden and Grigg 1980). By 1989, this satellite population had merged to form a continuous population from the Northern Rivers region of NSW into QLD (Seabrook 1991(Seabrook , 1993.…”

Do the numbers and locations of road-killed anuran carcasses accurately reflect impacts of vehicular traffic?

“…For example, scavenging has been reported in northern quolls ( Dasyurus hallucatus ; Burnett , Oakwood , Glen et al ), varanid lizards (Shivik and Clark , Cogger ), and snakes (Shivik and Clark , DeVault and Aaron ). Populations of avian predators, however, do not appear to be negatively affected by cane toads (Beckmann and Shine , Beckmann et al ). Raptor densities were high at our field site, with up to 69 birds counted along 4 km of road at sunrise (C. Beckmann, Deakin University, personal observation).…”