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As discussed, swimming ability within the siphonophores varies widely. The idea that siphonophore populations move up to the surface at dusk and back to depth at dawn in response to the waning and waxing illumination in near‐surface waters is not a compelling one, especially for the suborders with more limited mobility. Nonetheless, there is a substantial amount of data for many species that suggest precisely that. Moore (1949, 1953) reported vertical excursions of 30–40 m for many species of calycophorans in both the Florida current and in the vicinity of Bermuda on a day–night basis. Similar results were obtained by Musayeva (1976) for calycophorans in the Sulu Sea.

An alternative to a directed vertical migration triggered by sunset and sunrise is a slowly undulating change in vertical profile over a 24‐hour period (Pugh 1977). Siphonophores gradually move up and down with the changing photoperiod. This sinusoidal pattern of migration would explain the unusual depth profiles obtained for some weakly swimming species such as Hippopodius hippopus. The theory is still somewhat speculative.

Without question, a changing vertical distribution over the diel cycle is a characteristic of many siphonophore species. However, even among the calycophorans the vertical excursions are usually quite limited in scope (<50 m), a situation to be expected in an order that is morphologically adapted more for ambush predation than long‐distance swimming. Because of their float, the physonects are not only good acoustic targets, they face the same problems that fish with swimbladders do when moving vertically: expansion and compression of gas in their flotation system when moving up and down in the water column.