Dhr. T.J. (Dick) Dekker: “Hunting tactics of peregrines and other falcons”

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18 Feb 2009 16:00
Unit: Wageningen University
Location: Aula, building 362, Gen. Foulkesweg 1, Wageningen
Organisation: Wageningen University
Promotor: prof.dr. H.H.T. Prins (Resource ecology)
Promotor: Prof.dr. R.C. Ydenberg

 Half a century ago, Peregrines came close to extinction due to the poisonous residues of agricultural chemicals, but in recent decades the species has made a spectacular recovery. How the return of this superfast predator has affected the behaviour of shorebirds is a subject of scholarly research in Canada and the Netherlands. Certain waders are now lighter in weight than formerly. The explanation is that a fat bird has more difficulty evading a pursuer. And coastal sandpipers spend the high tide period in flight over the sea, instead of roosting on shore, where they run the risk of low surprise attacks by Peregrines. However, the hunting habits of wild falcons had been little studied. This is where Dick Dekker has made an important contribution. His dissertation presents data collected over 44 years in the field, during all seasons and in eight different Canadian habitats, as well as along the coast of Friesland. In total, he saw Peregrines capture 470 preys, of which 85% were waterbirds. In addition, 104 preys were taken by three other bird-hunting falcons under study: the Merlin, Gyrfalcon, and Prairie Falcon. The hunting success rates of migrating and wintering Peregrines ranged from seven to twelve percent, which means that roughly nine out every ten birds attacked managed to escape. However, breeding falcons had a higher capture rate because they specialized on juvenile gulls that happened to fly by the nest site. A remarkable discovery was that large falcons commonly robbed the smaller species, and that female Peregrines parasitized the (smaller) males. The biggest pirate of all was the Bald Eagle. This suggests that the return of the sea eagle to the Netherlands will have important implications for Peregrines.   
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