Seasonal shifts in insect ephemerality drive bat foraging effort

Animal foraging is fundamentally shaped by food distribution and availability.1Mueller T. Fagan W.F. Search and navigation in dynamic environments - From individual behaviors to population distributions.Oikos. 2008; 117: 654-664https://doi.org/10.1111/j.0030-1299.2008.16291.xCrossref Scopus (316) Google Scholar However, the quantification of spatiotemporal food distribution is rare2Hutto R.L. Measuring the availability of food resources.Stud. Avian Biol. 1990; 13: 20-28Google Scholar but crucial to explain variation in foraging behavior among species, populations, or individuals. Clumped but ephemeral food sources enable rapid energy intake but require increased effort to find,3Wiens J.A. Population responses to patchy environments.Annu. Rev. Ecol. Syst. 1976; 7: 81-120https://doi.org/10.1146/annurev.es.07.110176.000501Crossref Google Scholar can generate variable foraging success,4Real L. Caraco T. Risk and foraging in stochastic environments.Annu. Rev. Ecol. Syst. 1986; 17: 371-390https://doi.org/10.1146/annurev.es.17.110186.002103Crossref Scopus (265) Google Scholar and force animals to forage more efficiently. We quantified seasonal shifts in the availability of such resources to test the proximate effects of food distribution on changes in movement patterns. The neotropical lesser bulldog bat (Noctilio albiventris) forages in a seasonal environment on emerging aquatic insects, whose numbers peak shortly after dusk.5Hooper E.T. Brown J.H. Foraging and breeding in two sympatric species of neotropical bats, Genus Noctilio.J. Mammal. 1968; 49: 310-312https://doi.org/10.2307/1377989Crossref Google Scholar,6Dechmann D.K.N. Heucke S.L. Giuggioli L. Safi K. Voigt C.C. Wikelski M. Experimental evidence for group hunting via eavesdropping in echolocating bats.Proc. Biol. Sci. 2009; 276: 2721-2728https://doi.org/10.1098/rspb.2009.0473Crossref PubMed Scopus (140) Google Scholar We GPS-tracked bats and quantified nocturnal insect distribution in their foraging area using floating camera traps across wet and dry seasons. Surprisingly, insects were 75% less abundant and swarms were 60% shorter lived (more ephemeral) in the wet season. As a result, wet season bats had to fly twice as far (total and maximum distance fromroost distances) and 45% longer (duration) per night. Within foraging bouts, wet season bats spent less time in each insect patch and searched longer for subsequent patches, reflecting increased temporal ephemerality and decreased spatial predictability of insects. Our results highlight the tight link between foraging effort and spatiotemporal distribution of food and the influence of constraints imposed by reproduction on behavioral flexibility and adaptations to the highly dynamic resource landscapes of mobile prey.7Norberg R.A. An ecological theory on foraging time and energetics and choice of optimal food- searching method.J. Anim. Ecol. 1977; 46: 511-529https://doi.org/10.2307/3827Crossref Google Scholar,8Kohles J.E. O'Mara M.T. Dechmann D.K.N. A conceptual framework to predict social information use based on food ephemerality and individual resource requirements.Biol. Rev. Camb. Philos. Soc. 2022; 97: 2039-2056https://doi.org/10.1111/brv.12881Crossref PubMed Scopus (9) Google Scholar Examining foraging behavior in light of spatiotemporal dynamics of resources can help predict how animals respond to shifts in food availability caused by escalating environmental changes.