Predators’ consumption of unpalatable prey does not vary as a function of bitter taste perception

Abstract

Many prey species contain defensive chemicals that are described as tasting bitter. Bitter taste perception is, therefore, assumed to be important when predators are learning about prey defenses. However, it is not known how individuals differ in their response to bitter taste, and how this influences their foraging decisions. We conducted taste perception assays in which wild-caught great tits (Parus major) were given water with increasing concentrations of bitter-tasting chloroquine diphosphate until they showed an aversive response to bitter taste. This response threshold was found to vary considerably among individuals, ranging from chloroquine concentrations of 0.01 mmol/L to 8 mmol/L. We next investigated whether the response threshold influenced the consumption of defended prey during avoidance learning by presenting birds with novel palatable and defended prey in a random sequence until they refused to attack defended prey. We predicted that individuals with taste response thresholds at lower concentrations would consume fewer defended prey before rejecting them, but found that the response threshold had no effect on the birds’ foraging choices. Instead, willingness to consume defended prey was influenced by the birds’ body condition. This effect was age- and sex-dependent, with adult males attacking more of the defended prey when their body condition was poor, whereas body condition did not have an effect on the foraging choices of juveniles and females. Together, our results suggest that even though taste perception might be important for recognizing prey toxicity, other factors, such as predators’ energetic state, drive the decisions to consume chemically defended prey.

Seeing red? Colour biases of foraging birds are context dependent

“…Interestingly, we found that great tits consumed more unpalatable almonds when they were lighter, irrespective of which colour indicated unpalatability. This supports the idea that birds are more willing to consume chemically defended prey when they are in a poorer physiological condition (Barnett et al 2007(Barnett et al , 2012Skelhorn et al 2016;Hämäläinen et al 2020a). In contrast, we found the opposite effect in blue tits, with heavier individuals tending to attack more unpalatable food items than lighter birds.…”

Darwin’s small and medium ground finches might have taste preferences, but not for human foods

“…Medium ground finches fed most often on the bitter-flavoured pastry and wiped their beaks the least following its ingestion. This was surprising, given that bitter-tasting foods often elicit increased beak wiping in birds [25,54]. It is possible that our sample sizes were too small to detect preferences for human-food flavours, or that we did not add sufficient flavour to the pastry to be detectable.…”

“…latent), we predicted preferences would occur for such flavours across sites, regardless of the presence or absence of human foods. Potential taste preferences can be quantified as variation in feeding rate, or as variation in post-feeding beak wiping rate [25,[52][53][54]. Although beak wiping can clean the beak of debris [55], vigorous beak wiping commonly occurs after feeding on something unpalatable [25,54].…”

“…Therefore, we measured taste preferences in terms of consumption and beak wiping behaviour compared to two controls, neutral pastry that had no flavour added and bitter-flavoured pastry as a negative control. Bitter substances are aversive to many bird species, so we expected finches to consume less bitter-flavoured pastry compared to neutral or other flavoured pastry across all sites as well as to elicit more beak wiping behaviour [25,54] .…”

Evolutionary and ecological processes influencing chemical defense variation in an aposematic and mimetic Heliconius butterfly

“…Even high evolutionary potential will only lead to evolutionary changes if the defense trait variation influences predation rates (Speed et al, 2012). In general, empirical data on the impact of variation in defenses and its signaling on predators is lacking, but there is evidence for variation among predators in traits including perceptual abilities, individual motivation and tolerance to chemical defenses (Halpin et al, 2017;Briolat et al, 2019;Hämäläinen et al, 2020). Predators may also respond not only to average defense levels, but to the variation in them (Skelhorn & Rowe, 2005;Barnett, Bateson & Rowe, 2014).…”