Detection of earthworm prey by Ruff Philomachus pugnax

• Published in: Ibis
• Main Authors: Onrust, J., Loonstra, A.H.J., Schmaltz, L.E., Verkuil, Y.I., Hooijmeijer, J.C.E.W., Piersma, T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2017
• Subjects: Lumbricidae Rafinesque; 1815 [earthworms]; Philomachus pugnax; Ruff
• Online Access: http://imis.nioz.nl/imis.php?module=ref&refid=286422

Ruff Philomachus pugnax staging in the Netherlands forage in agricultural grasslands,where they mainly eat earthworms (Lumbricidae). Food intake and the surface availabilityof earthworms were studied in dairy farmland of southwest Friesland in March–April2011. Daily changes in earthworm availability were quantified by counting visible earthworms.No earthworms were seen on the surface during daytime, but their numberssharply increased after sunset and remained high during the night. Nevertheless, intakerates of individual Ruff in different grasslands measured during daytime showed the typicalHolling type II functional response relationship with the surfacing earthworm densitiesmeasured at night. Radiotagging of Ruff in spring 2007 revealed that most, if not all,feeding occurs during the day, with the Ruff assembling at shoreline roosts at night. Thisraises the question of why Ruff do not feed at night, if prey can be caught more easilythan during daytime. In March–May 2013 we experimentally examined the visual andauditory sensory modalities used by Ruff to find and capture earthworms. Five maleswere kept in an indoor aviary and we recorded them individually foraging on trays with10 earthworms mixed with soil under various standardized light and white noise conditions.The number of earthworms discovered and eaten by Ruff increased with lightlevel, but only when white noise was played, suggesting that although they can detectearthworms by sight, Ruff also use auditory cues. We suggest that although surfacingnumbers of earthworms are highest during the night, diurnal intake rates are probablysufficient to avoid nocturnal foraging on a resource that is more available but perhapsless detectable at that time.