Consumption of the lichen Roccella Gracilis by the large ground-finch Geospiza Magnirostris on the island of Daphne Major (Galápagos)

40 (2023) 34: 40–41 CONSUMPTION OF THE LICHEN ROCCELLA GRACILIS BY THE LARGE GROUND-FINCH GEOSPIZA MAGNIROSTRIS ON THE ISLAND OF DAPHNE MAJOR (GALÁPAGOS) Manuel Nogales¹* · Sandra Hervías-Parejo² Submi(ed 03 Jan 2023 · First decision 10 Jan 2023 · Acceptance 21 Feb 2023 · Online publica=on 26 Apr 2023 Communicated by Carlos Bosque DOI: 10.58843/ornneo.v34i1.1161 To date, some 19,000 species of lichen-forming fungi have been described, thriving in almost all terrestrial biomes (Lücking et al. 2017). Lichens are well known to produce a plethora of secondary metabolites, many of them with puta=ve an=-herbivore ac=vity (Boch et al. 2015). In addi=on, they produce a wide range of polysaccharides, many of which show relevant biological ac=vi=es (Solberg 1970, Svihus & Holand 2000, Akbulut & Yildiz 2010). Despite their poten=ally nutri=ous composi=on, habitual lichen consump=on by animals is rarely reported, except for some snails (Boch et al. 2011, 2015), weevils, the reindeer Rangifer tarandus (Sco(er 1965, Storeheier et al. 2002), the goose Branta bernicla (Rémy 2006), and pygmy parrots Micropsi6a spp. (Linck 2009. See Indiviglio 2012), and humans (Ivanova & Ivanov 2009). Rare consump=on of lichens by other mammals (Chamois Rupricapra rupricapra, and Alpine Ibex Capra ibex) (Boch et al. 2011) and birds (Corvus monedula; Sriskandan 2021) have also been recorded. However, birds generally use lichens to build their nests instead of using them as food (Rémy 2006). The observa=ons described here were made on Daphne Major (38.6 Ha; 120 m a.s.l.), an islet nearly in the center of the Galápagos Archipelago (0°25’21.03”N, 90°22’19.24”W). This islet contains an old volcanic tuff cone with a rela=vely large central crater and a small lateral craterlet. During a visit from 16 to 20 November 2018, we observed consump=on of the fru=cose lichen Roccella gracilis (Roccellaceae) by the Large Ground-Finch Geospiza magnirostris. This lichen grows on the branches of the small tree Bursera graveolens, which forms a small woodland in the upper part of this islet. Ini=ally, we considered the possibility that Large Ground-finches were foraging for small arthropods (basically, isopods and aphids) hidden inside the lichen structure. However, two observers further confirmed lichen consump=on on five different occasions from a short distance (3–5 m from the birds). During these feeding events, they consumed rela=vely small amounts of the lichen. It is possible that secondary compounds may limit inges=on by birds, yet the beneficial effect of biological ac=vity (e.g. an=viral or an=tumoral) on vertebrates is also well-known (Akbulut & Yildiz 2010). We did not observe this interac=on in another recent expedi=on to the islet during the same season (10–13th November 2022); it may not be a common event. The tendency of island animals to broaden their trophic niche is well-known (e.g. MacArthur et al. 1972, Traveset et al. 2015, Balza et al. 2020), and this behavior could be even more common on small islands with few trophic resources, par=cularly in dry years (see Grant & Grant 2014 and references therein). Further studies could show whether the birds eat lichens as part of their diet or for medicinal purposes. Our observa=on adds a piece to the larger puzzle of how island birds can survive on poor diets — of olen unusual food items— through opportunism and phenotypic plas=city. ¹ IPNA-CSIC, Ins=tute of Natural Products and Agrobiology, La Laguna, Tenerife, Canary Islands, Spain. ² IMEDEA, UIB-CSIC, Mediterranean Ins=tute for Advanced Studies, Esporles, Mallorca, Balearic Islands, Spain E-mail: Manuel Nogales · [email protected] Abstract · This note reports a trophic interac=on of a passerine consuming lichens. On the islet of Daphne Major (Galápagos Archipelago), we made five observa=ons of the Large Ground-Finch Geospiza magnirostris ea=ng the fru=cose lichen Roccella gracilis. This is an example of how island birds broaden their feeding niche in resource-poor environments. Resumen · Consumo de líquenes por uno de los pinzones endémicos de Galápagos. Describimos una interaccion trófica de un paseriforme consumiendo líquen. En el islote de Daphne (archipiélago de Galápagos), realizamos cinco observaciones del pinzón grande de =erra Geospiza magnirostris consumiendo el líquen de talo fru=culoso Roccella gracilis. Este es un ejemplo de cómo las aves insulares amplian su nicho trófico en un entorno de escasos recursos. Key words: Diet · Island ecology · Niche widening · Passerines · Trophic interacHon 41 ORNITOLOGÍA NEOTROPICAL (2023) 34: 40–41 ACKNOWLEDGMENTS We thank Ruben Heleno, Anna Traveset, and Peter and Rosemarie Grant for their valuable comments on an early version of the manuscript. Jens Olesen revised the manuscript, Roberto Jiménez (PNG) facilitated our work during the field expedi- =on, Sergio Pérez Ortega and Frank Bungartz provided us with general informa=on about lichens, and Aurelio Marwn provided us with interes=ng references. We thank the Charles Darwin Founda=on and the Galápagos Na=onal Park (research permit numbers: PC-88-18, PC-03-22-01). 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