Discrimination performance at different concentrations of the test feeder for the six experimental subjects.

<p>The sugar concentrations of the test options are given on the abscissa. Black circles represent the proportion of visits to the test feeder averaged over the two presentations of the same pairs of concentrations (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074144#pone-0074144-t001" target="_blank">Table 1</a>). The vertical dashed line indicates the standard option (20% w/w). The horizontal dotted line indicates the chance level at 0.5. Continuous lines give the non-linear fit based on Weber’s law model (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074144#pone.0074144.e005" target="_blank">Equation 5</a> with β = 1). Dash-dotted lines give the non-linear fit based on the near-miss to Weber’s law model (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074144#pone.0074144.e005" target="_blank">Equation 5</a> with β as a free parameter). The data point for Bat 4 at 50% sugar concentration (star) was excluded as an outlier.