I discussed how bottlenose dolphins scan the environment to make a decision and thus which performance strategies they adopted to solve the discrimination task. I also compared the performance in an identical echolocation task for porpoises (Wisniewska et al. 2012).

  • One of the dolphins used the same strategy in all sessions, showing a curving approach for the decision-making. This could be explained by some strategy adopted by other cetaceans swimming in circles to surround schools of fish or prey (Benoit-Bird, et al. 2009). This happened with one of the porpoises in Wisniewska et al. (2012) which frequently made curving approaches to the targets, covering larger distances and contributing to the longer trial durations.
  • In the case of the harbor porpoises, they made mistakes in 1.5–4% of trials with the PVC comparison target, 3–5% of trials with the brass target and 5–43% of trials with the steel target (Wisniewska et al. 2012). Thus, their errors percentages are lower than for both dolphins, and for all types of material. The better performance by the porpoises could be explained by them having been trained in many previous echolocation tasks, whereas the dolphins used here had never been trained in such contexts.
  • The difficulty for both animals increased when discriminating the steel and aluminum spheres, for which the echoes had similar spectra due to the smaller impedance differences between these materials (Au, 1993).
  • The aluminum sphere (the standard one), gives a rather even temporal signature, whilst the plastic gives a more complicated echo and lot of notches in the spectrum. This supplies many spectral and temporal cues for the animals to distinguish between them.
  • Our dolphins combined buzzes with horizontal (Schevill and Lawrence, 1956) and rotational head movements. These movements became pronounced when the dolphin was within the last meters from the target.
  • An average of eight scans (i.e. four scans per target) was made during one trial for the porpoises (Wisniewska et al. 2012). This is twice as many scans made by the dolphins, which on average have four scans per trial.


I observed clear differences between individuals of the same species in terms of ability to discriminate and use echolocation, but similar interspecies performance in relation to the materials chosen with the difficulty of the task

Surprisingly dolphins performed poorer than harbour porpoises. It is not known if this is because the dolphins had no history of echolocation training like the porpoises did, or if porpoise sonar is better than assumed.