Fig. 1. Red knots shift from mono- to diester preen waxes, the latter being more difficult to detect by a sniffer dog. (A) The shift from mono- to diester preen waxes (see inset) in spring takes place within 1 month in individual captive red knots (N=14 individuals; 95% confidence intervals around mean values of percentage of diesters are indicated by dots). (B) The likelihood of successful detection is a function of the type and amount of preen wax. Each data point represents detection success during 20 sessions (monoesters: black circles, diesters: open circles). Fits from the used logistic model (see Materials and methods) are depicted in the graph as lines (solid, monoesters: ln(P_detection/1–P_detection)=1.4519+0.6602xamount; broken, diesters: ln(P_detection/1–P_detection)=0.1786+0.6602xamount).