Notes on the Honey Buzzards Tracked by Satellite from Inverness 2001
The treks recorded for the two Honey Buzzard juveniles in 2001 at
Honey Buzzard Migration Maps
show a number of interesting features:
Both were thought to be late fledgers still being near their nests on 7th-8th September.
Both had moved significantly south west by 14th and 25th September respectively but had still
not left Scotland.
One bird then moved across northern Britain to reach Lancashire by 19th September while the other
lingered in Scotland and
moved into Northern Ireland by 29th September.
The faster mover was still only in Somerset on 9th October while the slower mover was in Wexford,
Eire, on 21st October. The
latter caused considerable interest in Ireland being only the 8th recorded since 1950.
After a substantial period of radio silence, the faster mover moved quickly to south east Spain by
23rd October, crossing the
Mediterranean to the Moroccan/Algerian border by 25th and north Morocco by 27th. No more signals were received from this
bird but the earlier long period of
silence may indicate that the radio was failing rather than the bird.
The slower mover was recorded out at sea 100 km SSW of Cape Clear on 29th October. Although connecting
the lines on the map might
indicate that it was flying SW, it is more likely that it had flown to Cape Clear and then moved due south.
Some comments:
The timing of the faster mover's migration, at least through northern England, appears to be
similar to that of two seen moving south
over Northumberland on 16th September this year (2001). Lingering this late is the norm in Northumberland with birds
typically fledging in the last week of August
and remaining in the nascent area for two further weeks. Indeed juveniles have been found in Northumberland on
breeding sites as late as the first week in November,
though whether they are locally bred or from Scotland is debatable.
Ireland may be an autumn trap for southward-bound broad-winged raptors. They follow the coast
down to Cape Clear and then have a hopeless
journey south of 800-900km to northern Spain:
Looking at Meyer, Sparr and Bruderer's paper on raptor migration strategy over the
Mediterranean (Behaviour 137:379-399,
notes)
such a journey would consume a minimum of c90g of
fat in a Honey Buzzard
compared to c13g of fat for a similar journey over land.
Of course we do not know that this Inverness youngster did actually perish but the loss of
signals from a previously reliable transmitter
and the adverse winds at the time make the odds very poor indeed.
The longest normal crossing across the Mediterranean is 290km from Tunisia to Malta. The
Mediterranean is a barrier but the number of islands
makes it less of a challenge than it appears at first sight. Juvenile Honey Buzzards do have a greater tendency
to cross the open sea in a southward direction as
they do not know where the bridges are (see Meyer et al above).
The 80km journey ESE from Wexford to Pembroke would have made a much more feasible sea crossing.
The inexperienced juvenile preferred to move
south rather than to make this crossing.
The difficulty of picking up low-volume Honey Buzzard movement is indicated by the difficulty
with which this bird was located in Ireland,
other than by the radio signals.
Of the broad-winged raptors, only the Osprey would appear to be capable of completing a sea
journey of almost 1,000km successfully.
The initial movement south west presumably results from the topology of the area with rather
daunting mountains to the south. This is
unfortunate for the juveniles' prospects as it tilts them towards the potential Irish trap.
