Foraging Behaviour and Food of Grey HeronsArdea cinereaon the Ythan Estuary

Publisher Website
Google Scholar
Abstract
First year gray herons were less efficient at foraging than adults. They made at least twice as many attempts to capture prey, but attained only 62% of the adult catch rate in terms of grams per min. Younger birds spent 1.8 times longer at foraging and foraged more at the less profitable high tide periods; they more often seized, then released, inanimate objects such as floating sticks and feathers. Three types of foraging behavior are described; stalking birds hunted at higher intensity, and at least 90% of fish captures were made then. Ythan estuary birds fed mainly on marine fish; invertebrate food was estimated at under 1% by weight; flatfish, especially flounder [Platichthys flesus], formed the bulk of the diet. The methods by which gray herons deal with their prey are described. Larger fish are held crosswise in the bill and shaken vigorously, perhaps to snap the spine; smaller fish (under 150 mm long) are often swallowed alive. Flatfish in particular are sometimes caught by spearing with the bill. There is some evidence of individual variation in ability to swallow large fish; on 5 occasions gray herons abandoned 200-300 mm flounder after attempting unsucessfully to swallow them, but 1 large juvenile swallowed a 260 mm flounder and a 375 mm sea trout [Salmo trutta].