Sympatric divergence of risk sensitivity and diet menus in three species of tit

Abstract

Divergent diet menus could cause sympatric divergence of risk sensitivity; however, evidence is not yet available for the functional link between diet menu and risk sensitivity. We investigated risk sensitivity (measured as the discount intensity for probabilistic rewards) and diet menu (insectivory and granivory) among three sympatric species of tits (family Paridae): varied tits, Poecile varius, marsh tits, Poecile palustris, and great tits, Parus major, which form mixed-species foraging flocks in Japan. Binary choice tests, offering rewards of differing amount and probability, were conducted in the laboratory. Great tits and marsh tits were found to be risk prone (and more insectivorous), whereas varied tits were risk averse (and more granivorous). Diet menus were examined in the laboratory using behavioural titration tests between sunflower seeds and mealworms. The results of these tests were similar to patterns of food exploitation determined using stable isotope analysis (δ13C and δ15N contents) of blood samples from birds collected in the wild. Possibly, the dominant varied tits drove the other two species of tits towards different diet menus and unusually high risk proneness. In future, we should examine whether different interspecies interactions cause different risk sensitivity in other geographical environments

Exploring Differences in Dogs’ and Wolves’ Preference for Risk in a Foraging Task

“…Hence wolves, that rely mostly on hunting, show a higher preference for risk as measured in the current study than dogs that rely more on scavenging, suggesting that the different ecological environments (and foraging strategies in particular) of wolves and dogs may have affected their preference/aversion for risk. The present results are in line with studies showing that more insectivorous tits are more risk-prone than more granivorous ones ( Kawamori and Matsushima, 2012 ), and that chimpanzees that rely more on seasonally fruiting trees are more risk-prone than bonobos that depend on more stable terrestrial vegetation ( Heilbronner et al, 2008 ). Taken together, these findings suggest that the less reliable and more transient the staple food source is, the more a species may be willing to take risks.…”

“…Wolves’ ‘feast-or-famine’ existence ( Mech et al, 2015 ) characterized by significantly riskier foraging situations, may have selected for a more risk-prone set of decision rules. Results are consistent with previous studies comparing chimpanzees and bonobos ( Heilbronner et al, 2008 ; Haun et al, 2011 ), and closely related tits with differing feeding ecology ( Kawamori and Matsushima, 2012 ), which converge in suggesting that the more transient and less reliable the staple food source of a species, the more likely they will show a preference for risk. Wolves and dogs are, to our knowledge, the first predator and scavenger species tested on a risk-foraging task, and considering the results, it suggests that further evaluation of predators and scavengers may provide interesting insights into which aspects of a species’ feeding ecology may affect preference for risk.…”

“…A comparison between three sympatric species of tits revealed that risk-preference was directly affected by their feeding ecology. Indeed the more insectivorous species were shown to be risk prone whereas the more granivorous species was risk averse ( Kawamori and Matsushima, 2012 ). Comparative work across primate species further supports the link between feeding ecology and risk preference.…”

Ways to be different: foraging adaptations that facilitate higher intake rates in a northerly-wintering shorebird compared to a low-latitude conspecific

“…Most previous studies comparing the foraging ecologies of closely related subjects examined differences in the context of sympatric niche differentiation (Benkman, 1993;Huey and Pianka, 1981;Kawamori and Matsushima, 2012;Labropoulou and Eleftheriou, 1997;Pulliam, 1985). Here, we compare two subspecies of the rock sandpiper: Calidris p. ptilocnemis Coues 1873 (hereafter ptilocnemis) and Calidris p. tschuktschorum Portenko 1937 (hereafter tschuktschorum).…”

Social dynamics of core members in mixed-species bird flocks change across a gradient of foraging habitat quality

“…Nonetheless, participation in mixed-species flocks can come at a cost when foraging-niche overlap between species intensifies interspecific competition among flock members [ 6 , 11 , 12 ]; but see [ 13 – 15 ]. Ultimately, the tradeoff between interspecific competition and flocking benefits depends on the degree of foraging niche segregation within a flock [ 15 , 16 ], as well as the abundance and distribution of food, and predation risk [ 8 , 14 , 17 ].…”