Timing of Honey-buzzard Movement within UK from 13-14 September 2008

Using the Honey-buzzard records on BirdGuides on 13/9 and 14/9 for which times were noted in the submission, a number of calculations were made:

• the numbers of Honey-buzzard moving, on an hourly basis, each day

  • through each county

  • through each region

• the average time at which the Honey-buzzard moved through each county, each day

The time was taken as the time reported for the observation. Occasionally interpolation was used to itemise individual sightings e.g. 4 birds from 10:30-11 would be treated as sightings at 10:30, 10:40, 10:50 and 11:00. Multiple sightings at a given time would be weighted accordingly e.g. 3 birds at 11:15 would be treated as 3 sightings at 11:15. 11:15 and 11:15. If the only time available was that at which the sighting was reported to BirdGuides, then the observation was ignored; similarly vague times like 'morning' and 'afternoon' were also ignored.

Tables 1(a) and 1(b) show the timing of the movements on 13/9 and 14/9 respectively on a regional basis.

Time BST	Midlands	NE England	East Anglia	SE England	Total by hour
06:01-07:00					0
07:01-08:00					0
08:01-09:00		1	1		2
09:01-10:00		7	2		9
10:01-11:00		13	10		23
11:01-12:00		6	20		26
12:01-13:00		4	19	1	24
13:01-14:00		20	12	2	34
14:01-15:00		12	5	1	18
15:01-16:00	1		1	1	3
16:01-17:00		1	1	1	3
17:01-18:00					0
18:01-19:00		3	1		4
Total by region	1	67	72	6	146

Table 1(a): Timing of Honey-buzzard Movement in UK on 13 September 2008, by region

Time BST	NE England	East Anglia	SE England	Scotland	Midlands	NW England	SW England	Total by hour
06:01-07:00		1						1
07:01-08:00	9	1	1					11
08:01-09:00	7	3	1					11
09:01-10:00	5	19	2					26
10:01-11:00	2	11	4					17
11:01-12:00	5	17	1					23
12:01-13:00	1	17	1					19
13:01-14:00	2	2	1		1			6
14:01-15:00	2	1	4		1			8
15:01-16:00	5		4		2	1		12
16:01-17:00	8		2					10
17:01-18:00	1	1	2	1				5
18:01-19:00								0
Total by region	47	73	23	1	4	1	0	149

Table 1(b): Timing of Honey-buzzard Movement in UK on 14 September 2008, by region

Tables 1(a) and 1(b) show the hourly pattern during each day of the major movement. The peak for all regions is from 10:01-15:00 on the 13/9 and 09:01-13:00 on the 14/9. These migration times are just what would be expected in normal movement with birds avoiding the start and finish of each day, when visibility may be poorer, and taking advantage of the higher temperatures in the middle of the day, which facilitate improved buoyancy. There is no difference in the peak between NE England and East Anglia on 13/9, which suggests that the birds are following a standard migration pattern, starting their flights early morning and moving for 5 hours. On the 14/9 the pattern is similar except that the peak runs one hour earlier, perhaps because the weather was better on the morning of 14/9 than on 13/9.

What is very obvious is that the vast majority of birds moving through East Anglia disappear from the UK at this point and do not exit from the south coast, as in the 2000 movement. It was established elsewhere that, on both 13/9 and 14/9, the great bulk of the birds moved directly from East Anglia to Benelux, crossing the southern extreme of the North Sea and extending their daily trek by at least 3 hours.

While most birds crossed the southern North Sea, there was still a small, steady movement through SE England, taking place in the afternoon from 12:01-17:00 on 13/9 and running all day on 14/9 from 07:01-18:00. This movement is thought to be of birds moving through East Anglia earlier and keeping due S, rather than moving E/SE across the North Sea. Another subtlety is that on 14/9 the movement continues at a significant level in the afternoon in NE England, perhaps because of the movement of Scottish birds from further N. So there is apparently some ripple effect from Scotland to NE England and from East Anglia to SE England, the discussion of which is dealt with below when the individual county information is available.

Table 2 shows the average time, and earliest and latest times, at which Honey-buzzard passed through each county recording area on 13/9 and 14/9. The prime reason for looking at events on a finer-grained county basis is that this might show ripple effects, where birds moving through one county, were subsequently recorded in another county further S. On the 13/9 there is very little evidence for ripple effects: the average times in counties far apart such as Northumberland and Durham, about 13:15, and Norfolk and Suffolk, about 12:20, are quite similar. Indeed throughout NE England the average times range from 12:09-13:18 for Northumberland, Durham, Cleveland, N Yorks and Lincs, with E Yorks earlier at 10:47 and S Yorks later at 15:11. This pattern is consistent with a synchronised movement from the hinterland to the coast, with birds commencing their migration inland in their breeding areas on improving weather conditions and moving SE/E to the coast, as observed at Stocksfield by NR. The pattern is inconsistent with a ripple effect whereby the birds start say in Northumberland and move S through each county in turn. It could be argued that the birds had arrived over the North Sea in a broad front from the E; however, in this case some of the birds would be expected to be moving W, rather than the observed E/SE, and the behaviour would be expected to be much more chaotic after such an arduous journey of say 600 km from Denmark, with birds clearly seeking resting and feeding areas; as discussed elsewhere claims for a small number of birds moving 'in-off' are unconvincing, such records being much more likely to simply reflect the layout of the coast, or even observer wish-fulness. There is one obvious ripple effect – between Norfolk and Suffolk – with average times of 11:57 and 12:43 respectively. So the birds moving through Suffolk may have already been seen in Norfolk, around an hour earlier.

On 14/9 there is an early rapid rush across Lincs (in NE England) and Norfolk (in East Anglia). 20 birds move through Lincs with average time 08:38 and 58 through Norfolk with average time 10:50. This movement is likely to be of birds moving through NE England on 13/9 that had roosted in S Yorks/E Yorks/Lincs overnight (13/9-14/9), having travelled perhaps 150-250 km on 13/9 from their breeding areas in 4-5-hours flight at 40-50 kph; for instance Newcastle-Doncaster is 165 km, Hexham-Lincoln is 217 km. This suggests that the early birds flying through Lincs and Norfolk were not new birds: they may have already been observed the day before in NE England; further the Norfolk birds on 14/9 may have been seen earlier in Lincs. In SE England passage is later than in East Anglia with average time of 13:30 against 11:00; further the passage had apparently diminished with 23 birds timed in SE England as against 73 in East Anglia. Again this looks like a ripple effect from East Anglia to SE England. But as on 13/9 the flow seems to have mainly moved off SE/E, again to Benelux to join the major exodus there. The birds passing through SE England are those that chose not to cross the southern North Sea, maybe mainly juveniles who relied on their instincts to adopt a southward drive. Further north, in NE England in Northumberland, Durham, N Yorks, E Yorks and S Yorks, the later average time varying from 12:25-15:58 than in Lincs of 08:38 indicates a further fresh arrival from the hinterland and from the north in Scotland.

Table 2: Earliest, Average and Latest Time of Honey-buzzard passing through each County Recording Area on 13 and 14 September 2008

An obvious question is: how many birds were observed? Taking the ripple effects literally, then the Suffolk totals should be subtracted from the total for 13/9 and the Lincs, Norfolk and Suffolk totals should be subtracted from the total for 14/9. However, it is not thought such precise calculations are warranted: there are so many variables in the data set such as proportion of actual movement passing over a station being observed on the ground, the proportion of the actual movement passing over unobserved areas, and the proportion of the actual movement being accurately identified at a station. If the movement was partially inland, then the proportion detected will be substantially reduced as in September most observers are on the coast; compounding this problem is the perhaps controversial view that observers inland, say patch-workers or vismig specialists, are less likely to identify Honey-buzzard than rarity seekers on the coast. There is also the question of whether the totals should reflect numbers reported on BirdGuides or the numbers established after County Records Committee review. While the latter would be the normal preference, the politics surrounding the Honey-buzzard, the uncertain standards for identifying Honey-buzzard and the reluctance of observers to submit formally records to their County Records Committee, make this a difficult choice. This matter will be discussed again.

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