Its mid-March and a spell of wet and windy westerlies
come to an abrupt end. Overnight a
light north-westerly changes to a light south-easterly and the unlocking of the
nature reserve gate at dawn is accompanied by two squeaking noises.
One comes from the heavens in the form of a northbound Meadow Pipit, the
other from a nearby hawthorn bush. The
spring passerine migration season has started in earnest (with apologies to the
two Stonechats seen the previous week).
It is not always like that, however.
The bushes were silent during spring 1997 with only two individuals
trapped and ringed. Yet the 1996/7
winter itself was not a major problem for winter survival.
Why were 24 ringed in spring 1996 and only 8 in autumn, yet the two
in spring 1997 were followed by 178 in autumn?
The ringing effort has been similar throughout with the exception of
spring 1988 which has been discounted from any analysis.
| Year |
Spring |
Autumn |
|
1985 |
18 |
|
Here the effects of the hard winters in 1985/6, 1990/1
and 1995/6 can be seen. However, we
have to remember that this species is a partial migrant. Therefore a proportion of mostly young birds risk a 400+ mile
journey from northern Britain to southern Britain/northern France undertaken as
a series of short night migrations. What
appear to be mainly adults remain at or near the breeding grounds.
Therefore any differences in winter conditions between northern and
southern Britain need to be taken into account.
A look at the 1995-7 figures throws up the following:
a)
Extremely
poor survival by adults remaining on the breeding grounds during the 1995/6
winter
b)
Better
survival by the mainly young birds which moved south (hence better than expected
numbers in spring 1996 at Heysham).
c)
Poor
weather during the 1996 breeding season in northern Britain, coupled with very
low numbers of adults which had already bred once (therefore more
‘experienced’ if you can really use this term with a species which lasts for
two breeding seasons at best), was
assumed to have led to atrocious numbers on autumn passage in 1996. Indeed, there were only three actual sightings during the time-slot for birds of north-British origin in
September and most of the paltry total involved a small influx of continental
birds (& a Firecrest) in mid-October.
d)
Predictably
low numbers in spring 1997 as there were very few birds to return
A
noticeable feature of springs 1998 and 1999 has been the earlier nature of the
spring passage with hardly any April records in 1999! This first came to notice with the presence of a
Firecrest on Westgate for 7/2–8/2/98
only. Searching for this bird
revealed several Goldcrests already obviously on passage and a similar check of
Heysham Obs. revealed similar small numbers of unringed (therefore not the
wintering) birds. Peak numbers
appeared at the end of March with relatively few into April.
1999 again saw what were probably early migrants during late February and
then a very large fall on 17/3, a week earlier than any sizeable arrival in
earlier years. Smaller numbers
passed through during the remainder of March but there were virtually no records
in April, even during good fall conditions in the first week, which produced
sizeable numbers of Chiffchaffs and early Willow Warblers
Passing
reference has already been made to continental birds. These are presumed to originate from Scandinavia or perhaps
the Baltic states but there is a possibility that some do come from further east
in north-west Russia. Their arrival
is always ‘telegraphed’ by reports of Goldcrest falls on the east coast
although, in some instances, a reflection of these falls does not reach ‘our
side’ due to a change to westerly type weather conditions.
Arrivals have sometimes coincided with Yellow-browed Warblers or, in one
case, a Pallas’s Warbler. The
only really large arrival of
birds of continental origin followed a huge fall on the east coast during
the previous week and involved over 150 present (in a limited area of the nature
reserve) with 50 trapped on 27/10/90, a significant proportion of the autumn
ringing total. The highest proportion
of continental birds in autumn has already been referred to (1996).
The
effect of poor weather during the breeding season has already been alluded to
with reference to 1995-7. It was
also apparent in 1998. Spring
1998 should have seen the theoretically highest breeding population of the
period under review. Yet numbers
during September were relatively poor after what, by common consent, was an
appalling breeding season in northern Britain.
Retrap
data and ringing recoveries reveal that the passage of birds of north-British
origin is leisurely, involving quite a bit of lateral movement (e.g. Calf to
Heysham and Walney to Heysham movements during the same season). However, one
recovery took this to extremes and reminded Spurn observatory workers that you
cannot be too presumptuous re-the origin of presumed ‘in-off’ (the sea)
Goldcrests! It was ringed at Heysham Obs. on 27/9/97 and controlled at
Spurn on 15/10/97. There have been
winter-period recoveries from Dorset (2), Greater London, Staffordshire and
breeding season recoveries from the Mull of Kintyre and Northumberland.
One of the most fascinating, however, was ringed during a strong
north-easterly airflow, which produced Siberian Rubythroat and Red-flanked
Bluetail in Dorset and Leicestershire respectively.
Surely of continental origin, it was ringed on 18/10/97 and, helped by
the overnight tailwind, controlled on Anglesey during the morning of 19/10/97.
Hopefully
this short article has revealed the interesting information, which can be
obtained through operating an observatory-type ringing station. This
type of operation is particularly helpful in the study of partial migrants such
as Goldcrests and Robins where very little that is meaningful can be gathered
from casual observations. Indeed,
how many readers realise that Robin is the most consistently common medium to
long distance night migrant through Heysham from late August to early October? An article will be prepared for a forthcoming
Newsletter.
Pete
Marsh (September
1999)