Hovering hawkmoths dining from flowers won't have to chase their meals over long distances, but if the wind picks up they need to track flower movements so that they can keep hovering in the best spot and feed effectively. But this comes at a cost: contracting flight muscles to accelerate or decelerate the body and track a flower is energetically expensive. Interested to know more about moth tracking behaviour, Jordanna Sprayberry and Thomas Daniel at the University of Washington investigated how well moths can feed from and track moving flowers, and then used a mathematical model to predict whether the moths were losing out on vital energy when tracking(p. 37).
To measure tracking movements, the team filmed moths feeding from motor-operated robotic flowers moving at frequencies of 1-3 Hz. They also measured feeding rate. When the team moved the flowers vertically or horizontally, they found that moths could feed at the same rate, at all frequencies. However, when they moved flowers towards or away from the moths,they could only feed at movement frequencies up to 2 Hz, and fed at a lower rate, indicating that moths struggle to feed from flowers moving in this way. Calculating overall tracking ability by measuring a moth's distance from a flower and the time delay between the flower moving and the moth following,they found that moths were best at tracking flowers moving horizontally at a low frequency, and worst with flowers moving towards and away from them at a high frequency.
Using their mathematical model to estimate the energy needed to track the flower, and comparing it to the energy in each moths' meal, the team found that they don't lose out by tracking flowers, as the extra energy needed to track is minimal compared to the benefits of a proper meal. The team suspect that if a moth can track a flower, it will feed, but if it is struggling to follow a flower it will cut its losses and not attempt to feed at all.