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Volume 17 Issue 2 Pages 59 - 99 (October 2000)

Citation: Green, R.(2000) Avian Predation by Captive Otters. IUCN Otter Spec. Group Bull. 17(2): 83 - 84

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Avian Predation by Captive Otters

Rosemary Green

Vincent Wildlife Trust, Barjarg, Barrhill, Girvan, KA26 0RB, Scotland

Abstract: During fifteen years of keeping otters, no predation on birds was observed until the winter of 1999-2000. Freshly killed birds offered to otters had not apparently been recognised as food. In the winter of 1999, a sub-adult captive otter stalked and killed a variety of birds - two pheasants, two gulls, a thrush and a goose. Otters in the adjacent pen caught and ate a heron.

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Predation on birds had not been observed in fifteen years of keeping captive otters, until the winter of 1999-2000, although many otters had proved adept at catching voles and amphibians. Before that time, road killed birds had been offered to otters to introduce them to the range of potential prey available after release. The otters had appeared not to recognise the dead birds as food, playing with them and dropping them into their pools. On occasions otters would chase songbirds or run at crows (Corvus corone) or herons (Ardea cinerea), which were stealing their fish. However these incidents appeared to be play or threat displays, rather than a serious attempt to catch the birds. Herons and crows had formed the habit of taking fish, with sometimes as many as six herons flying up the valley to the otter pens at feeding time and several families of crows being reared partly on stolen fish. The effect of the otters' digging and constant pressure of their feet within the pens was to create a plant community of annual weeds different from the surrounding fields. This attracted pheasants (Phasianus colchicus) and songbirds to visit regularly to take advantage of the seed bearing plants. On one occasion seven wintering wrens (Troglodytes troglodytes) were observed using the entrance tunnel of an occupied otter sleeping box for the night.

In early winter 1999 a sub adult female otter from the Scottish Borders was found one morning with the freshly killed body of a hen pheasant in her sleeping box. The feathers were disordered, but the skin was not broken. Vomit, full of chewed feathers was also present in the sleeping box. Over the next two nights the young otter learnt how to deal with feathered prey and consumed all but some feathers, the legs and larger bones of the pheasant. It was not known whether she had caught and killed the bird or simply taken advantage of a death from other causes. However, in the following winter months this otter was seen stalking other birds. She caught and ate another hen pheasant, a songthrush (Turdus philomelos), a herring gull (Larus argentatus), a black headed gull (Larus ridibundus) and a goose. The goose was so completely eaten that only one leg and a few wing feathers were left. It was tentatively identified as either a barnacle goose (Branta leucopsis) or a small Canada goose (Branta canadensis) (Paul COLLIN, pers. comm.). In the neighbouring pen two siblings from Shetland also caught and ate a heron, possibly having learned the behaviour from their neighbour's example.

ACKNOWLEDGEMENTS - Paul Collin, RSPB is thanked for identifying the grisly remains.

Resumen: Predación sobre aves por parte de nutrias en cautiverio
Hasta el invierno de 1999-2000 no se había observado predación sobre aves en 15 años de mantenimiento de nutrias en cautiverio. Hasta entonces se les había ofrecido aves atropelladas para introducirlas al rango de presas disponibles tras la liberación. Estas no parecían reconocer a las aves muertas como alimento pero jugaban con ellas y las tiraban a sus piscinas. En ocasiones las nutrias perseguían aves canoras o corrían a los cuervos o garzas que les robaban pescado. Sin embargo, estos incidentes parecían ser juegos o despliegues de amenaza más que intentos serios de cazar a las aves. El efecto de escarbar y la presión constantes de las patas de las nutrias sobre el suelo de los encierros facilitó el establecimiento de una comunidad de malezas anuales distintas a la de los campos linderos. Esto provocó las visitas regulares de faisanes (Phasianus colchicus) y aves canoras para aprovechar las semillas de dichas plantas. A principios del invierno de 1999 una nutria subadulta fue encontrada una mañana con el cuerpo fresco de un faisán. Las plumas estaban desordenadas pero la piel no estaba rota. También había un vomito lleno de plumas masticadas. A lo largo de las 2 noches siguientes la nutria aprendió a tratar a la presa emplumada y consumió toda la carcasa salvo algunas plumas, las patas y algunos huesos largos del faisán. No se supo si la nutria había cazado y matado a la presa o simplemente aprovechado una carcasa fresca, sin embargo, en los meses siguientes esta nutria fue vista acechando otras aves. Cazó y comió otro faisán, un tordo (Turdus philomelos), gaviotas (Larus argentatus y L. ridibundus), y un ganso. En un encierro vecino 2 hermanos también cazaron y comieron una garza, posiblemente tras haber aprendido el comportamiento de su vecina.
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