02/10/2009
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Autumn arrivals - tracking northern thrushes

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Every birder has favourite sights and sounds that carry personal significance each season; perhaps the whistling of Wigeon in winter, Cuckoos calling in spring or summer parties of screaming Swifts. For me, the sibilant ‘tseeep’ of unseen Redwings passing overhead on chilly nights in early October is one of the most evocative indications of the arrival of autumn.

Both Redwings and Fieldfares have already started reaching us this year, with BirdGuides records totalling thirteen and five respectively at the time of writing, but the main arrival is still to come. This article considers what we expect to happen over the next few weeks and looks at how you can use BirdTrack and BirdGuides to monitor and display the pattern of further arrivals of these two charismatic indicators of autumn.

Fieldfare

Ringing studies of Scandinavian Fieldfares show that fewer than 1% of the population move more than 30 miles from their nest sites by the end of September, so it’s not surprising that BirdGuides’ September records for each of the past three years are in single figures (see Tables 1a–c). The main migratory departure is in October and, like many other species, the adults tend to leave first.

Fieldfare
Fieldfare, Tring, Hertfordshire (Photo: Nick Moran)

Fieldfare numbers can be expected to build up throughout October. BirdTrack weekly reporting rates (Fig. 1) show that we can anticipate Fieldfares featuring on 7% to 15% of all complete BirdTrack lists by the middle of the month, with the peak reporting rate for the entire year (approximately 20% of all complete lists) for both 2007 and 2008 being the last week of October.


Figure 1 BirdTrack Weekly reporting rate for Fieldfare 2007-09 (Graph: BTO)

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Redwing

Two distinct races of Redwing pass through or winter in this country. Fennoscandian breeders of the nominate race Turdus iliacus iliacus winter over most of western Europe, including Britain and Ireland. A smaller population of the race T. i. coburni breeds in Iceland and the Faroe Islands. The bulk of the population of this race winter in Ireland and northwest Iberia but there are also many late-autumn ringing recoveries from Scotland and western France. This race is rare in England; there have only been two English ringing recoveries, the first in Cornwall as recently as January 2005. The coburni race is a fraction larger and darker, its main distinguishing fieldmarks said to be heavier streaking on the throat, more extensive olive-brown coloration across the flanks and under-tail coverts, more merging of the brown streaks on the chest-sides and a stronger buff tinge to the sides of the head.

Redwing
Redwing, Tring, Hertfordshire (Photo: Nick Moran)

The earliest BirdGuides records of Redwing over the last 3 years are a fraction earlier than those of Fieldfare, with an average first date of 8th September compared to 12th for Fieldfare (see Tables 2 a-c). Both BirdGuides records and the BirdTrack weekly reporting rate (Fig. 2) show an interesting arrival pattern in 2007, when there was an influx of Redwings in the last week of September involving a large number of birds. This is nicely illustrated by the diverging green and blue lines in Fig. 2 and the numerous individuals recorded on BirdGuides from 27th–28th September, including a sizeable visible migration count from West Yorkshire of 3825 birds (Table 2c). Figure 2 also illustrates that the bulk of Redwing arrivals can be expected mid-month, following a very similar pattern to Fieldfare. Perhaps the most spectacular migration event of recent times involved Redwings; an enormous movement of several hundred thousand thrushes, mainly of this species, was witnessed across northwest England on 9th–10th October 2004.


Figure 2 BirdTrack Weekly reporting rate for Redwing 2007-09 (Graph: BTO)

Pressures on the populations

Large areas of both species’ breeding ranges have a very low human population density so human activity is unlikely to have much direct effect on their breeding success. However, hunting does continue to put pressure on both species and it accounts for the majority of ringing recoveries of Redwing in southern Europe.

Like many other species, though, the main concern is climate change; Fieldfares have already begun expanding their breeding range in a southwesterly direction but the consequences of further alteration have yet to be revealed. Recording the arrival times of these migrants is just one way we can start to detect and understand how bird movements are being influenced by climate change.

Using BirdTrack to monitor migration

BirdTrack provides free online recording software for birders, and for those already familiar with it, it has been evolving! The homepage recently had a face-lift to make it much more user-friendly. Changes include fewer menus across the top and neat boxes for the key options, making it easier to register/login, to select one of the stunning BirdTrack wallpapers or to check the brand new BirdTrack flickr pool. Start recording this autumn’s arrivals by registering now!


New look BirdTrack homepage (Screenshot: BTO)

Maps & Reports is a useful tool for displaying data from any area of Britain and Ireland over the past seven years; the animated maps for Fieldfare and Redwing are set to make really interesting viewing throughout October as northern thrushes arrive en masse.

Table 1a) Fieldfare on BirdGuides September 2009

DateAreaCount
1st  Shetland1
12th  Cork1
15th  Nottinghamshire3
19th  Suffolk1
23rd  Lothian8
Total records5
Total individuals14

Table 1b) Fieldfare on BirdGuides September 2008

DateAreaCount
16th  Lincolnshire12
20th  Cumbria1
20th  Suffolk1
25th  London3
26th  Lancashire1
28th  Cornwall1
Total records6
Total individuals19

Table 1c) Fieldfare on BirdGuides September 2007

DateAreaCount
20th  North Yorkshire15
26th  Suffolk1
27th  West Yorkshire5
28th  Ayr3
Total records4
Total individuals24

Table 2a) Redwing on BirdGuides September 2009

DateAreaCount
5th  Lincolnshire1
11th  Manchester6
12th  Cumbria1
15th  Lancashire1
16th  Kent1
18th  East Yorkshire1
18th  Worcestershire20
19th  Kent2
19th  Lincolnshire2
21th  Norfolk2
23th  Buckinghamshire5
23th  Lothian1
28th  Somerset4
Total records13
Total individuals47

Table 2b) Redwing on BirdGuides September 2008

DateAreaCount
15th  Dorset1
16th  Aberdeenshire1
24th  Dorset3
24th  Lancashire21
25th  London10
25th  South Yorkshire4
27th  Kent4
Total records7
Total individuals44

Table 2c) Redwing on BirdGuides September 2007

DateAreaCount
5th  East Yorkshire1
13th  Surrey1
15th  Suffolk1
16th  Kent3
16th  Norfolk1
18th  Cleveland1
18th  East Yorkshire1
18th  Kent16
18th  Norfolk1
18th  West Yorkshire2
19th  Norfolk1
20th  Kent1
20th  North Yorkshire15
21th  Hampshire2
22th  West Yorkshire2
26th  Bedfordshire1
26th  Suffolk2
27th  Cumbria2+
27th  Dorset3
27th  Norfolk1
27th  West Yorkshire3825
27th  West Yorkshire130
28th  Nottinghamshire50
28th  Powys2
28th  Scilly11
Total records25
Total individuals4076
Written by: Nick Moran, BirdTrack Organiser, BTO