Hunting tactics of Peregrines and other falcons
toon extra info.
|[S.l. : s.n.]|
|192 p fig., graf., tab.,  p. pl|
|Proefschrift Wageningen toon alle annotatie(s)
Met lit. opg. - Met samenvatting in het Engels en Nederlands
|Ydenberg, Prof. Dr. R.C. ; Prins, Prof. Dr. H.H.T.|
|Samenvatting door auteur||
This dissertation describes the foraging habits and capture rates of four species
of bird-hunting falcons; Peregrine (Falco peregrinus), Merlin (Falco columbarius),
Gyrfalcon (Falco rusticolus), and Prairie Falcon (Falco mexicanus).
Eight of the nine study areas were situated in western Canada in widely different
habitats, and the observation periods intermittently included all seasons over 44
years, 1965–2008. The various chapters report and compare the location-specific
hunting methods and choice of prey of these falcons in the following scenarios:
(1) Migrating Peregrines hunting waterbirds at Beaverhills Lake, a large wetland
in central Alberta; (2) Migrating Peregrines and Merlins capturing small shorebirds
and passerines at Beaverhills Lake; (3) Breeding Peregrines that launched
their hunts from the high chimneys of an industrial powerplant by a large
Alberta lake and selectively took gulls; (4) Marine Peregrines nesting on Pacific
island cliffs and preying on seabirds; (5) Peregrines and other raptors hunting
wintering Dunlins (Calidris alpina) and ducks at Boundary Bay on the Pacific
coast of British Columbia; (6) Peregrines specializing on teal and American
Wigeon (Anas Americana) wintering on coastal farmlands; (7) Territorial pairs
of Peregrines and Prairie Falcons competing for prey and nest sites on a
sympatric breeding range along an Alberta river; (8) Prairie Falcons and Gyrfalcons
wintering in the city of Edmonton and capturing Rock Doves (Columba
livia); (9) Gyrfalcons hunting Mallards (Anas platyrhynchos) wintering on
Alberta farmlands; (10) Klepto-parasitic interference from eagles and buteo
hawks with hunting Peregrines and Gyrfalcons, and intra- and interspecific prey
theft between falcons.
The largest set of data pertains to the Peregrine, which was studied in all seasons
and habitats except during winter in central Alberta. At Beaverhills Lake,
Peregrines on spring migration attacked avian prey on 674 occasions and captured
52, a success rate of 7.7%. Success rates for adult falcons and spring immatures
were respectively 9.8% and 7.1%, not significantly different. Fall immatures
had a success rate of 2.4%, but the sample was small. Waterfowl and
shorebirds made up 94% of prey taken. Stealth approaches and long-range surprise
attacks were the major strategies in 70% of hunts. Hunting Peregrines
often soared at great altitudes and stooped low to attack flying prey or to flush
sitting prey. The effectiveness of surprise strategies at the lake was facilitated by
shoreline vegetation. In addition, Peregrines used a number of other, more unusual,
hunting methods. A few prey were taken on the ground or in shallow
water, all others were seized in the air and borne down. The majority of birds
caught failed to use escape tactics routinely employed by their kind. Lone prey
individuals were more often killed compared to individuals in flocks.
Peregrines wintering on the Pacific coast attacked Dunlins 652 times with 94
captures, representing an overall success rate of 14.4%. Adult falcons achieved
26.8% success in 164 hunts, significantly higher than the 9.0% in 399 hunts by
first-year Peregrines. The hunting strategies of these wintering falcons differed
from the tactics deployed at Beaverhills Lake. The open coastal mudflats did not
facilitate a stealth approach. Only 35% of Peregrine hunts at Boundary Bay were
surprise attacks and 62% were open attacks on flocks. Hunts over the mudflats
or ocean had a success rate of 11%, as compared to 44% over the shore zone.
Some very long and persistent pursuits of sandpipers were made by immature
Peregrines and Merlins.
During high winter tides that inundated all mudflat habitats, the Dunlins departed
and stayed well offshore for periods of 1.5 to 6.5 hours. Termed overocean
flocking, this flight behaviour is believed to be an anti-predator strategy.
After the tide began to recede the Dunlins landed in the shore zone where they
were at their most vulnerable to surprise attacks by Peregrines. Captures recorded
per hour of observation peaked at 0.25/hour in the two hours following the
crest of the high tide, four times higher than two hours prior to high tide. The
hypothesis is advanced that nearness to vegetation increases the Dunlin’s predation
risk, which was strongly supported by the data.
The hypothesis that the hunting success rate of breeding Peregrines is greater
than that of migrating or wintering falcons was supported by data collected at an
Alberta nest site. The adult pair had an overall rate of 30.3% in 386 hunts. Over
the course of the 7-year study the rate increased from 21.9% in the first year to
39.1% in the seventh year. The majority (77%) of attacks were initiated from
high soaring flight, and the falcons used the exhaust of the plant’s smokestack to
gain height for soaring. Of 117 prey captured 62 (53%) were Franklin’s Gulls
(Larus pipixcan), and 85% of a total of 81 gulls known to have been killed by
these falcons were juveniles.
Peregrines breeding on an island off the northwest Pacific coast hunted seabirds
such as murrelets by direct aerial pursuit or by striking them on the water.
If the swimming bird was hit and crippled by the attack, the falcon turned back
to pick it up from the surface of the water. The success rate of these falcons was
22% in 73 observed hunts.
In hunting small passerines and small shorebirds, the Peregrine’s success rate
was 8.2% in 647 hunts as compared to 12.4% in 354 hunts by Merlins. The
Merlin was significantly more successful than the Peregrine in capturing small
passerines (12.2% vs. 3.8%) but not in hunting small shorebirds (12.6% vs.
The majority of ducks (82%) taken by Peregrines were, in order of frequency,
American Wigeon, Northern Pintail (Anas strepera), Northern Shoveler (Anas
clypeata), and teal (spp.). Mallard hens were rarely captured but no drakes were
seen killed. Mallards of both sexes were preyed upon by Gyrfalcons wintering in
Alberta. Their success rate in 70 hunts was 22.8%. Gyrfalcons wintering in Edmonton made 141 attacks on Rock Doves with a success rate of 10.6%, significantly
different from the 26.0% success of a Prairie Falcon in 104 attacks on city
Klepto-parasitic interference was commonplace between falcons and larger
raptors. In British Columbia, Peregrines and Gyrfalcons lost captured ducks to
Bald Eagles (Haliaeetus leucocephalus) and Golden Eagles (Aquila chrysaetos).
In Alberta and the Netherlands, Peregrines were robbed by buteo hawks. As
well, interspecific and intraspecific prey theft was frequent between falcons, and
females routinely robbed conspecific males.
In addition, this thesis reports on the population dynamics and nest site competition
between Peregrines and Prairie Falcons on a sympatric breeding range
in Alberta over a span of 48 years. The Peregrine became extirpated during the
1960s. Large-scale efforts to reintroduce the species in the 1990s seemed initially
successful, resulting in seven new breeding pairs, but they dwindled to one,
while the Prairie Falcons continued to do well.
The first chapter of the thesis details 15 years of Peregrine migrations at a
large lake in central Alberta, and the last chapter analyses the fall passage and
hunting habits of Peregrines along the Wadden Sea coast of the Netherlands.
There, the specific research question was whether or not Dunlins wintering on
the Dutch coast would engage in over-ocean flocking manoeuvres during high
tides that inundate all mudflat habitats. The phenomenon proved to be very rare
and the probable reasons are discussed in detail.
|Trefwoorden (cab)||falconidae / falco / foerageren / voedingsgewoonten / prooi / eenden / diergedrag / canada / nederland / voedselketens|
|Diergedrag en ethologie / Aves|
|Toelichting||De slechtvalk was bijna uitgestorven door giftige residu’s van landbouwchemicaliën, maar de stand heeft zich hersteld. Dekker deed onderzoek naar de invloed van de terugkeer van deze roofvogel op zijn prooisoorten in Nederland en Canada. Hij heeft gegevens verzameld van 44 jaar, in alle seizoenen en in acht verschillende Canadese landschappen, alsmede aan de Friese waddenkust. In totaal zag hij slechtvalken 470 prooien slaan. Daarvan bestond 85 procent uit watervogels. Daarnaast werden er 104 prooien gepakt door drie andere valkensoorten uit deze studie: het smelleken, de giervalk en de prairievalk. Het jachtsucces van trekkende of overwinterende slechtvalken varieerde van zeven tot twaalf procent.|