Fliers and perchers among Odonata: dichotomy or multidimensional continuum? A provisional reappraisal

We revisit the hypothesis, first advanced in 1962, that, with regard to their means of thermoregulation and overt behaviour, two types of Odonata can be recognised: fliers, when active (during reproductive activity, primarily, or foraging) remain on the wing, whereas perchers, when similarly engaged, spend most of the time on a perch from which they make short flights. First, in light of the available data, we restrict the hypothesis to apply primarily to activity at the rendezvous. Next, we review evidence, including direct measurements of body temperature coupled with activity budgets, to test the proposition that the hypothetical classification constitutes a dichotomy rather than a continuum. We conclude: (1) that there is merit in retaining the dichotomous classification into fliers and perchers, together with the thermoregulatory capabilities assigned to each category; (2) that the distinction between fliers and perchers is sufficiently discrete to be a useful predictor of the suite of thermoregulatory strategies and energy demands characteristic of representatives of each category; and (3) that, within each category a continuum exists such that the capacity to heat the body by irradiation (i.e. ectothermically) or by metabolic heat production (endothermy) increases with body size. Some departures from expectation based on the percher/flier dichotomy reflect the increased flight activity that occurs at the rendezvous under conditions of heightened conspecific or interspecific interference. Other apparent anomalies are identified as topics for potentially fruitful research.