Deep-diving pilot whales make cheap, but powerful, echolocation clicks with 50 µL of air

Echolocating toothed whales produce powerful clicks pneumatically to detect prey in the deep sea where this long-range sensory channel makes them formidable top predators. However, air supplies for sound production compress with depth following Boyle’s law suggesting that deep-diving whales must use very small air volumes per echolocation click to facilitate continuous sensory flow in foraging dives. Here we test this hypothesis by analysing click-induced acoustic resonances in the nasal air sacs, recorded by biologging tags. Using 27000 clicks from 102 dives of 23 tagged pilot whales (Globicephala macrorhynchus), we show that click production requires only 50 µL of air/click at 500 m depth increasing gradually to 100 µL at 1000 m. With such small air volumes, the metabolic cost of sound production is on the order of 40 J per dive which is a negligible fraction of the field metabolic rate. Nonetheless, whales must make frequent pauses in echolocation to recycle air between nasal sacs. Thus, frugal use of air and periodic recycling of very limited air volumes enable pilot whales, and likely other toothed whales, to echolocate cheaply and almost continuously throughout foraging dives, providing them with a strong sensory advantage in diverse aquatic habitats.

Otolith δ13C values as a metabolic proxy: approaches and mechanical underpinnings

Knowledge of metabolic costs associated with maintenance, foraging, activity and growth under natural conditions is important for understanding fish behaviours and the bioenergetic consequences of a changing environment. Fish performance in the wild and within a complex environment can be investigated by analysing individual-level field metabolic rate and, at present, the natural stable carbon isotope tracer in otoliths offers the possibility to reconstruct field metabolic rate. The isotopic composition of carbon in fish otoliths is linked to oxygen consumption through metabolic oxidation of dietary carbon. The proportion of metabolically derived carbon can be estimated with knowledge of δ13C values of diet and dissolved inorganic carbon in the water. Over the past 10 years, new techniques to study fish ecology have been developed, and these can be used to strengthen the application of otolith δ13C values as a metabolic proxy. Here, we illustrate the great potential of the otolith δ13C metabolic proxy in combination with other valuable and well-established approaches. The novel approach of the otolith δ13C metabolic proxy allows us to track the effects of ontogenetic and environmental drivers on individual fish physiology, and removes a major obstacle to understanding and predicting the performance of free-ranging wild fish.

Landscape context alters cost of living in honeybee metabolism and feeding

Field metabolic rate (FMR) links the energy budget of an animal with the constraints of its ecosystem, but is particularly difficult to measure for small organisms. Landscape degradation exacerbates environmental adversity and reduces resource availability, imposing higher costs of living for many organisms. Here, we report a significant effect of landscape degradation on the FMR of free-flying Apis mellifera , estimated using 86 Rb radio-isotopic turnover. We validated the relationship between 86 Rb k b and metabolic rate for worker bees in the laboratory using flow-through respirometry. We then released radioisotopically enriched individuals into a natural woodland and a heavily degraded and deforested plantation. FMRs of worker bees in natural woodland vegetation were significantly higher than in a deforested landscape. Nectar consumption, estimated using 22 Na radio-isotopic turnover, also differed significantly between natural and degraded landscapes. In the deforested landscape, we infer that the costs of foraging exceeded energetic availability, and honeybees instead foraged less and depended more on stored resources in the hive. If this is generally the case with increasing landscape degradation, this will have important implications for the provision of pollination services and the effectiveness and resilience of ecological restoration practice.