Gross Volume, Regional Distribution and Direction of Honey Buzzard Movement through the UK in Autumn 2008

Gross Volume

The base UK data compiled from BirdGuides and analysed by day, region and direction is available here. Table 1 shows by region the gross numbers recorded on BirdGuides through September 2008 in the three main periods, identified as 1st-12th September with few birds moving before the big exodus, 13th-21st September when by far the bulk of the movement occurred and 22nd-30th September when a steady but smaller outflow occurred. Only very obvious duplicates have been removed from the counts.

Table 1: Gross Numbers Recorded on BirdGuides in September 2008 by Region of UK

The highest numbers of Honey Buzzard are usually found in SE England, East Anglia and NE England. Clearly regions further south have a tendency to record higher totals as the birds from further north usually pass through them. 2008 is remarkable therefore for the counts in East Anglia and NE England being considerably higher than in SE England. In 2000 SE England recorded the highest counts as birds departed from the south coast of England to France. From the coverage point of view NE England is covered well on the coast but poorly inland. East Anglia and SE England are presumed to be better covered, certainly in inland areas. Looking at the individual days from 13th-21st September for these 3 regions, we see the unusual regional pattern in Table 2.

Table 2: Gross Numbers Recorded on BirdGuides in the three Main Regions from 13th-21st September 2008

So it appears that high numbers passing through East Anglia on 13th/14th did not follow through into SE England. We can see some individual examples of this. For instance where did the 18 moving S at Minsmere on 13th from 10:25-13:25 go? Indeed although there may be some duplication, where did the 184 birds passing though East Anglia from 13th-14th go? On the figures above, they did not pass through the well-watched SE corner. Later in the period from 19th-21st we see the pattern more as expected with numbers in SE England lagging slightly and matching the counts in East Anglia. Comparative numbers in NE England and East Anglia are well-matched throughout, suggesting a synchronised movement (perhaps weather-related) rather than a rippled one through the two regions.

Table 3 shows the directions in which the birds were moving in September 2008 for the UK as a whole. Direction S-E means the birds were recorded as moving towards compass points between S and E, and SW-W towards compass points between SW and W. Trek means that no direction was given in terms of compass points, the birds being recorded as flying ‘over’, ‘in-off’ or between geographical locations; it is in principle possible to analyse the last named but this has not been attempted yet. The ‘in-off’ category is considered further below. Other includes birds flying towards compass points with a northerly component, basically NE, N or NW, or simply resting. Clearly it would be useful to break down the sizeable Trek component into compass points and the current high numbers of birds in this category must be regarded as a limitation of the data set.

Table 3: Direction of Honey Buzzard Movements in the UK in September 2008

The reason for classifying the compass points as above is to distinguish between birds moving in a westerly direction and those moving in a southerly direction or a continent-leaning direction of SE/E. The results show that the numbers moving S-E heavily outnumber those moving SW-W by slightly over 4:1 with 81% of the birds in the month going in this direction. Further the proportion moving S-E is quite constant throughout the month being lowest at 65% in the first 12 days and highest at 86% on 14th, 87% on 15th, 93% on 18th and 86% from 22nd-30th. Thus at no time is there any indication of an influx of birds over the North Sea spreading westerly over the country.

By region the %S-E is 83% for NE England, 88% for East Anglia, 63% for SE England, 72% for the Midlands, 94% for SW England, 50% for Scotland and 83% for NW England. The regions where a westerly movement would be expected if birds were coming in off the North Sea are NE England and East Anglia but 83% and 88% respectively of birds in these areas are moving S-E. The almost total absence of ‘in-off’ records in NE England also supports the idea that the birds here were not coming off the North Sea.

East Anglia was the only region where ‘in-off’ birds were recorded on a significant scale (about 5% of total). Other records were in NE England on the south side of the Humber, hence crossing this estuary from further N, with an isolated record in County Durham. A further breakdown was made for East Anglia showing more precise directions, as shown in Table 4.

Table 4: Breakdown of Direction for Honey Buzzard Movement in East Anglia in September 2008

The 16 birds recorded as 'in-off' records on the coast included (from BirdGuides):

13/9

Norfolk (north): Blakeney Point (09:12), East Runton (10:57), Cley (11:35);

Norfolk (north-east): Horsey (moving inland, 10:35), Waxham (11:10), Trimingham (mid-morning), Waxham (moving inland, 11:30), Waxham (12:32);

Norfolk (east): Caister-on-Sea (early morning, 2 birds);

Suffolk (north-east): Lowestoft (moving inland, 08:43), Corton (12:45, 2 birds).

14/9

Norfolk (north): Wells Woods (06:50).

15/9

Norfolk (north): Sheringham (09:50).

20/9

Norfolk (north) : Titchwell (no time).

Six of the 16 birds were recorded from north Norfolk where it is most likely that they had crossed the Wash and made landfall on the southern side. The records on 13th September from further east in Norfolk and in north-east Suffolk are much more interesting. It is possible that these birds have also crossed the Wash but are pushing out further to the east and making landfall again as they skirt the coast.

On 14th the direction through East Anglia seems quite unusual with 19 birds moving E and four SE. These included six E at Welney, Norfolk, at 12:10, at least nine E at Burnham Overy, Norfolk, from 10:30-11:15, and three SE at Cantley Beet Factory, Norfolk, at 13:00. On 18th five birds moved SE at Beetley, Norfolk, at 11:45. Overall in the month there is a definite eastward lean in the East Anglia data with slightly over half as many birds going E/SE (57) as going S (112). Almost three times as many birds (57) are going E/SE as are going SW/W (20).

It is necessary to consider the presence of quite large numbers of Common Buzzard in the movement. This is surprising as it is too early for the migration of significant numbers of Common Buzzard from Scandinavia. British-bred Common Buzzard are said to be sedentary. However, some clues come from Prytherch [2013]. The population has been rising rapidly: “The population [in Avon] rose from 13 pairs in 1982 to 105 pairs in 2012” … “The study population was probably self-supporting throughout and latterly it appeared to produce more adults than it could absorb” [Abstract]. Later [p.276] he comments: “On maturing they might have tried to settle locally, but were forced to move away. Some other juveniles disperse widely and either settle without returning or move back to their natal area ... Therefore, many new adult birds in my study area (or in other similar areas) now have little choice but to move elsewhere in order to establish territories. Most 'empty' ground was likely to be to the east.”

So Common Buzzard migrants in UK in autumn, particularly in eastern areas, are likely to be British birds, irrupting from breeding areas. The rise in Common Buzzard migrants in eastern areas has nothing to do with a Scandinavian origin as is supposed in some quarters. It's obviously more romantic to treat a Common Buzzard migrant as of continental origin but the reality is that it's British, seeking space for a territory. There's very little evidence for migration of continental birds through Britain from ringing returns; further, dramatic increases in UK passage are correlated with increased UK populations, not with unchanged populations on the continent.

It is likely that a number of observers are not aware of the similar appearances of juvenile Honey-buzzard and Common Buzzard. So Common Buzzard, as the safer default identification, may have been over-estimated and Honey-buzzard juvenile underestimated.

Summary

The gross number of birds, with obvious duplicates removed, recorded in September 2008 is 886. Of these 622 were recorded in the three main regions of East Anglia, NE England and SE England. Numbers in SE England were relatively low. The direction of flight, where noted, was predominantly between S and E (81%) for the UK as a whole and even higher in East Anglia alone at 88%. At no time is there any indication of an influx of birds over the North Sea spreading westerly over the country. Further analysis of the East Anglia data shows that the small number of in-off records (5% of total for the region) may be attributable to birds crossing the Wash or trying a more ambitious sea-crossing further to the east. There is a definite eastward lean to the movement in East Anglia.

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