Honey-buzzards in Lincolnshire with special reference to the 2000 invasion
The Honey-buzzard pernis apivorus is one of those enigmatic British birds the status of which has been clouded in mystery and rumour for the last hundred years. Only recently has some public light been shed on the status and habits of the British population with the publication of a revealing paper in British Birds (BB92.7.326).
Its true status as a breeding bird in Lincolnshire may still be one of the surprises of the new millennium.
Honey-buzzards are exclusively summer visitors to northern Europe breeding in large numbers in favoured areas and yet even where numerous being secretive and in-obvious. Pairs have bred in locations in Britain close to roads and sites frequented by birdwatchers for many years without being discovered.
The unpredictable nature of its occurrence in Lincolnshire means that the discovery of one of these aerial masters is always marked with some excitement. I well recall my first encounter with a Lincolnshire Honey on May 23rd 1986. En route from Scawby to Greetwell the sight of large raptor soaring over a corn field by the side of the road caused an immediate emergency stop that produced amazing views of a superb male Honey-buzzard, no more than 200m away, gliding and soaring up into the blue sky. It even went into some brief wing-clapping display over the nearby woodlands before drifting out of sight. Unfortunately in spite of further searching it was not seen again. When seen well adult Honey-buzzards are not too difficult to identify but distant views often lead to confusion with Common Buzzard. Autumn juveniles are a different story. Differing in profile and plumage to adults they are distinctive if you know them well but to the inexperienced may well be passed off as Common Buzzards. The best reference to raptor identification is undoubtedly The Raptors of Europe and the Middle East by Dick Forsman.
Prior to 2000 there had been a total of 80 Honey-buzzards recorded in Lincolnshire excluding 1999 (for which information was unfortunately not available). The first recorded occurrence of the species was of one shot, on an unspecified date, at Scotton in 1850. Following another undated record in 1864 four occurred in both autumn 1886 and 1908. Of the former four all occurred in September one being was shot at Market Rasen while three of the latter foursome were shot and the fourth seen in September. The first records had thus established the pattern of autumn occurrence of juveniles. It was another twenty-nine years before the next Honey-buzzard was to be recorded in the county when one was seen at Limber on June 30th 1947. Two more summer records, one caught in a trap at Horkstow on July 1st 1951 and another at Limber from July 2-3rd 1955, quickly followed this bird. Thus the first fifteen records showed that Honey-buzzards could occur as passage juveniles in autumn and as wandering, possibly prospecting, adults in mid-summer.
From September 30th 1967 when one was seen at Tetney records started to become more regular as the number of birdwatchers in the county increased and coastal coverage in autumn began to take on a new vigour. As shown in the following charts the species has remained as a fairly erratic vagrant since that time with a number of years failing to produce any records. Others years have revealed small clusters of birds mainly in autumn, late August to early October, but also in spring late April to early June and mid summer July-mid August. There has however, been an obvious increase in the number of birds occurring during the 1990s. Records have increased during all periods but not necessarily in the same years. Thus a year with a good spring influx may have few autumn birds and vice versa. The increasing number of mid-summer records suggests that the species may just be breeding at some localities within the county or at least be seriously looking for suitable nesting woodlands. Splitting the recent records into 1967-1982 and 1983-1998 inclusive shows the recent evolution in occurrence pattern very neatly. In the former period autumn records predominate 19 against just 2 in spring summer whereas in the latter spring-summer records have become more regular with 26 against 21 in autumn. The latter pattern is more impressive given the notable autumn arrival in 1993 when 10 juveniles were recorded between September 14th and October 3rd.
All of the birds prior to 1967 were found at inland localities no doubt partly a reflection of the distribution of observers, the shooting fraternity and gamekeepers during the period. It is perhaps surprising that the early coastal recorders like Caton Haigh did not acquire any Honeys in autumn given their record with small passerines. Analysis of the records from 1967 onwards reveals that the coastal bias continues. Of the total of 69 records 58 came from coastal localities, including the Wash, and just 11 from inland sites. The seasonal split shows 17 spring 6 summer and 35 autumn coastal records with 2, 4 and 5 respectively for inland sites. It may be significant that of the 11 inland records 7 (63%) have occurred since 1992 compared to 28 (48%) of the 58 coastal records during the same period.
Not allowing for any spring and summer Honey-buzzards in 2000, of which there was at least one, the autumn total of 97 birds exceeded the total for the previous 150 years! Such was the scale of the movement through the county that on the peak day, September 20th, a minimum of 44 Honey-buzzards were seen in the county over half the county total to 1999. First inkling of the invasion were one or two birds seen on Sunday 17th with one in off the sea at Huttoft at 10:05 and perhaps the same bird south-east at Gibraltar Point at 12:39. In human terms Tuesday September 19th was a foul day on the east coast with a fresh to strong south-easterly wind combined with continuous often torrential rain. In Honey-buzzard terms it was must have been just about the worst scenario for a juvenile bird setting out on the first part of its unaided journey to central Africa. Leaving southern Scandinavia or the Baltic states in good flying conditions they must have suddenly come across the northward moving front with reduced visibility and heavy rain probably while over the sea or somewhere over northern Germany or the Netherlands. Once drifted out over the North Sea with no obvious land in sight, to put down for a rest, they would have had no option but to carry on flying probably through the night until they hit the east coast. Such was the orientation of the weather front that most birds seem to have arrived on a front from Northumberland and Durham to Lincolnshire. A few birds appeared further north with odd ones in Shetland and one unlucky youngster made it all the way to Iceland, forming that countrys 5th record, only to die from injuries sustained on arrival.
In order to try and get some more information on Honey-buzzard migration I posted a query on the Euro-birdnet internet site and I am very grateful to Hans Schmid of the Swiss Ornithological Institute and Dr Mikael Hake of the Grimso Wildlife Research Station Sweden for the following information regarding Honey-buzzard migration strategy. In summary adult Honey-buzzards migrate 2.5 to 3 weeks earlier in the autumn than juveniles with the vast majority having left Europe by August to early September. Adults and juveniles adopt different migration routes based on this difference in timing. Adults migrating earlier in the autumn can rely on thermal activity for soaring which saves energy and thus are able to take a longer route via mountain ranges and the shortest sea crossing like Gibraltar and the Bosphorus. They also make longer stop-overs en route to feed. Later in the autumn juveniles have to rely on more costly flapping flight and thus take a shorter and more southerly route involving sea crossings over the central Mediterranean. Satellite tracking of Swedish Honey-buzzards has shown that on average it takes an adult 45 days to travel from Sweden to its wintering area in central Africa an average of approximately 170km per day. These timings did however, include stop-over days when birds presumably fed en route through Germany, Denmark and France. A juvenile tracked in 1998 covered 5342km in just 23 days departing on September 15th and arriving in NW Nigeria on October 7th. This gives an average travelling speed of 232km per day. Interestingly data for satellite tracked birds from 2000 showed that two adult females had already crossed into Africa via Gibraltar by September 2nd. Two juveniles took different routes one going south via Italy reached Africa on October 4th but the second bird may give a clue to the origin of the British birds. Having moved south from Sweden it stayed in Denmark from September 8th-13th but was then drifted west and recorded from the Netherlands on September 19th the date of the easterly gales in Lincolnshire. The individual in question presumably managed to avoid the drift across the North Sea moving south through central France to cross the Pyrenees between 28th and October 1st before crossing the Straits of Gibraltar on 2nd and reaching Nigeria by 14th.
Figure 1. Lincolnshire Honey Buzzard Records 1947 -1999
Figure 2. Peak Autumn (September-October) passage Honey Buzzards including 2000.
Figure 3. Lincolnshire Honey Buzzards records 1967-1999
September 19th-October 4th.
In a brief respite in the rain a single juvenile arrived at Saltfleetby mid afternoon on the 19th flying off south-west inland. Being a Wednesday there were not many birders on the Lincs coast on the morning of the 20th but those that made it were quickly treated to the start of one of the most amazing birding spectacles to hit the county. Juvenile Honey-buzzards appeared to be coming in off the sea and turning south-west as they headed inland low over the fields. Four were picked up in the first two hours of daylight at Saltfleetby but observers at Gibraltar Point took the cream with 22 birds passing by 10:45 and a day total of 25 individuals. The most impressive flock of six birds was watched moving south over the fields inland from the reserve. Some of these birds appear to have skirted the Wash, no doubt they had seen enough water over the previous days journey, with records from Witham Mouth, Framton Marsh, Moulton and Holbeach St Matthew during the morning. Others quickly penetrated inland with one flying towards Kenwick Top (Louth) mid morning, one at Marston sewage farm and two at Ewerby. The largest single flock of the whole invasion though concerned seven birds seen together at 13:15 at Cherry Willingham heading towards Lincoln. Clearly the birds seen on the 20th were just the tip of a very big iceberg. There were few birders in the field with it being mid week and after the initial flurry of birds along the coast passage there seemed to halt with later birds presumably pushing quickly inland as the weather conditions improved. It would be mere speculation to guess at the number of birds that may have passed through the county that day but records of a flock of five over the Humber at Spurn and others from inland sites in Yorkshire suggest that more were missed than were seen.
Coastal records after the 20th were few; three at Gibraltar Point 21st and 4 on 22nd with 1 24th were outnumbered by inland occurrences but were birds still arriving over ensuing days or were the individuals seen simply leftovers from earlier arrivals further north reorienting themselves?. More people were clearly on the look out for Honey-buzzards after the initial news of the arrival but could this explain the pattern of records after the 20th? A total of 11 were seen on 21st and 15 on 22nd, both weekdays but on the first Saturday 23rd, with lots of eager birders out looking at their local patches only four individuals were picked up all day. On the Sunday there were just two at Gibraltar Point and Friskney Decoy and it seemed that the passage was over. On the 21st single juveniles had been seen moving south at Barton at 08:40, south at Risby Warren 09:45, Gibraltar Point 3 and Framton Marsh 1 all south, 2 at Elm near Wisbech going south-east and one over Toft Newton Reservoir. Five of the birds on 22nd were in the Barton-Horkstow area all going south with other southward movements at Aisthorpe near Scampton, near Scunthorpe west, and 4 at Gibraltar Point with two south-west at Croft Marsh and a single inland at Aswarby Thorns.
All of these birds could have arrived on the 20th and stopped off for a day or two searching for food at inland woodlands before moving on south but was there then a further arrival of birds in the clear anticyclonic weather of the 25-27th?. Of the eight birds seen on 25th I picked up seven at Laughton forest. Having been actively searching for Honey-buzzards from mid morning it was 14:03 before I saw any at all and then by a piece of pure good fortune. Scanning east over the forest I picked up a large raptor gliding on set wings and loosing height. A further scan revealed four more birds all in a line moving in the same direction all presumably having coming out of a thermal somewhere to the north. They then picked up another thermal over the forest and soared up wards for ten minutes until they disappeared into the base of the cloud layer. How many more parties had passed the same way and over the width of the county during that afternoon? Two further singles passed the same locality at a lower altitude the same afternoon but all seemed intent on pressing on southwards. Only one bird was seen on the 26th at Donna Nook, a new arrival? And just two on 27th one clearly searching for food at Broughton woods and another attempting to move south over Risby Warren but being constantly drifted back north by a fresh wind. Somewhat surprisingly six birds were picked up on the 26th with a pale phase juvenile tracked heading inland for one and a half miles at Saltfleetby before it turned south-west and one at Stenigot a favoured site for soaring raptors on the Wold edge. The remaining birds were all at Laughton forest. One moved purposefully south picking up a series of thermals from the forest while the others appeared to be clearly looking for food as their flight and behaviour was typical of foraging birds (Lars Svensson pers com). A single bird at Tattershall 29th and a pale juvenile at Gibraltar Point October 4th tied up the invasion. By the latter date most birds were leaving the south coast of Britain with some large concentrations noted at southern headlands.
All of the birds seen that were aged were juveniles, as would be expected from the timing of the movement. Only two birds were definitely of the pale form, which is very distinctive and may even be confused Osprey, but one at Ancaster on 23rd was said to be pale? Surprisingly the two definite pale birds both occurred at the end of the movement at Saltfleetby September 28th and Gibraltar Point October 4th. The majority of the remaining birds were of the dark form although a few were of the more rufous or mottled form described by Forsman.
Few other raptors seem to have been involved in the movement the exception being Ospreys of which about 11 birds were seen over the ensuing ten days following the main arrival on the 22nd. The most appreciated of these were two juveniles that subsequently took up residence at Tetney Lock where they fished in the canal and local fishing pond much to the chagrin of some of the owners. Unusually both of these birds stayed into early November with at least one to 4th.
For those people who experienced the invasion of the Honey-buzzard memories will last long but will there ever be a chance to experience another event like it in the county? The weather conditions that led to the movement were a classic of drift migration theory. A huge static area of high pressure had been sitting over Scandinavia, the low countries and east through the Baltic to western Siberia for weeks. What was needed then was a fast moving, deep low pressure system arriving from the south-west and moving up through northern France and the Netherlands bringing a sudden change from clear bright skies to heavy rain with strong south-easterly winds. This depression arrived on 19th and moved into the North Sea providing the rain and poor visibility needed to drift the Honey-buzzards and other migrants onto the British east coast. Exactly the same conditions led to the previous mini-invasion in September 1993 when the gale hit on September 13th. It may well be that a combination of a good breeding season in the source area has to be combined with the correct weather conditions to provide a good Honey-buzzard drift across the North Sea. The events of 2000 were unprecedented in British ornithological history and it seems unlikely that they will be repeated but as the saying goes never say never again.