Fishy tales: Behaviour of schooling fish escaping from terns
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Tularam, GA
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Abstract
The aim of this study is to develop a better understanding of seabird foraging behaviour and the anti-predator behaviour of their prey. Studies of seabirds’ foraging and prey-capture behaviour, as it relates to the evasive and escape behaviour of schooling fish, are sparse. Our study was carried out at One Tree Reef on the southern end of the Great Barrier Reef, Australia. A school of hardyheads Pranesus capricornensis sheltered in the shallows over the sand flats in front of the research station for 14 non-consecutive days. In that time, Lesser Crested Terns Thalasseus bengalensis were observed for 10 hours from above the surface in 37 foraging bouts and for 40 minutes from underwater in at least one foraging bout. In each foraging bout, a single tern dived into the school. We found that terns on average dived at a rate of 0.67 ± 0.35 dives/minute from 4–5 m above the surface. The depth range of dives was 43–58 cm. Therefore, fish within 58 cm of the surface were potentially accessible. The total length of the hardyheads was 10–12 cm, which is within the size range useable by terns. Fish used flash expansion to escape diving terns and formed a vacuole around birds as they slowly ascended to the surface. This escape manoeuvre was effective about 80% of the time. The fish that were caught did not respond to the escape movements of the fish above them and, therefore, were isolated. Fish also used the C-startle response to escape terns underwater and in mid-air. The anti-predator manoeuvres of hardyheads are similar to those observed among Clupea spp. (herrings and sardines) and Ammodytes spp. (sand eels) escaping sub-surface predators. Hardyheads and sardines react in the same way to gannets Morus spp. and terns that plunge dive directly to their prey, partially confirming the prediction that results for plunge-diving gannets are generalisable to other gannets and boobies (Sula spp.), terns and gulls (Larus spp.), tropicbirds (Phaethon spp.), pelicans (Pelecanus spp.), and kingfishers (Alcedinidae).
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Marine Ornithology
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49
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1
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© The Author(s) 2021. This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Biological oceanography
Ecology
Marine and estuarine ecology (incl. marine ichthyology)
Evolutionary biology
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Hulsman, K; Tularam, GA, Fishy tales: Behaviour of schooling fish escaping from terns, Marine Ornithology, 2021, 49 (1), pp. 159-166