Fig. 7. Testing the response of blue petrel (Halobaena caerulea) chicks and fledglings to odors in the field. (A) The Porter method. A light bulb warms the chick to induce a `sleeping' state (1). Puffs of odor are presented to the chick (2) and the reaction is scored following the convention of Porter et al. (Porter et al., 1999) [adapted from Cunningham et al. (Cunningham et al., 2003)]. (B) Responses to DMS using the Porter method. Average response scores to DMS (10 pmol l^–1, filled bar) and control (open bar, distilled water) solutions. Values are means + s.e.m. Differences are significant (Wilcoxon signed-rank test, P<0.03, N=22 chicks, 15–20 days old). (C) A blue petrel near fledging age. (D) Blue petrel fledglings orient towards DMS (10^–12 mol l^–1) in a Y-maze. The histogram shows the percentage of birds that chose DMS or control. NC indicates no-choice. P<0.01, binomial test, N=24. Photograph provided by G.A.N. [data from Bonadonna et al. (Bonadonna et al., 2006)].