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Hunting tactics of Peregrines and other falcons - Section: 20 Page: 174 - Discussion and synthesis

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174

Huntin tactics of Pere ines

The safety aspect of flock formation. In the above described observations, it was very evident that the city pigeons, by massively flushing from the buildings or ground, actually made it easier for the falcons to affect a capture, whereas free-flying single pigeons pursued by Gyrfalcons escaped or were let go, except in one case in which a pigeon was chased and grabbed directly from behind. This pigeon probably had not seen the falcon coming (Chapter 13).

This suggests that the tendency of prey species to take to the air at the sight of a falcon and to form dense flocks which is generally seen as an anti-predator strategy not only draws the attention of the predator to the birds, but the birds seem to invite attention. In fact, flocks of shorebirds actually approach and track the falcon's movements (Buchanan et al. 1988). By doing so, they compromise the safety of the flock while individual birds find shelter inside the flock. This applies to Merlins and Peregrines attacking Dunlins at Boundary Bay, as well as to Prairie Falcons and Gyrfalcons hunting city pigeons.

The flocking habits of feeding shorebirds in regards to individual spacing and predation risk have been studied by several researchers (Cresswell 1994; Quinn and Cresswell 2004; Van den Hout et al. 2008). But it is an open question which class of prey either the adults or the juveniles, or perhaps only the strongest flyers among them find their way into the centre of flying flocks. Conversely, it remains to be determined which category of individuals is relegated to the less safe outside. As shown in this thesis, Peregrines attacking dense flocks of Dunlins tend to concentrate on the edges or bottom of flocks (Chapter 9).

Do parent Peregrines teach their fledgling how to hunt? The question of whether or not juvenile Peregrines have to be taught hunting skills by their parents has been raised before and answered convincingly by the releases of captive-raised juveniles that are now thriving in the wild (Cade and Burnham 2003). Apparently, chasing and grabbing hold of other birds comes naturally to young falcons. Nevertheless, there was a gap in detailed knowledge about parent-fledgling interactions (Newton 1979). In that regard, the observations reported here have added substantially to this debate (Chapter 10). Furthermore, this study has also shown convincingly that Peregrines gain in expertise and success rate as they become older, another subject about which, to my knowledge, there was no prior information available in the raptor literature.

A final note on the pesticide era, and the food base as the ultimate determinant in raptor dynamics. A question that was particularly relevant at the start of this study was whether the Peregrine would survive the pesticide era in view of the alarming reports about eggshell thinning and breeding failures. My findings of 35 years ago that immatures made up the majority (62 72'/o) of spring migrants came as a surprise (Chapter 2). Evidently, these northern migrants were still hatching young at what appeared adequate levels, which was later confirmed by intensive research conducted by government biologists on the coast of the Arctic Ocean. Evidently, despite rather high pesticide levels, Canadian tundra-breeding falcons continued to reproduce with erratic ups and downs

OCR
Tag: burnham eggshell falcon falcons fledgling flock flocking flocks gyrfalcons parentfledgling peregrine peregrines pesticide pigeon pigeons reproduce shorebirds

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