A Typical Honey-buzzard Season in Northumberland and Main Techniques Used

The techniques are split into two parts. In the first, the main techniques used from 1993-2003 are described. These techniques were also used in 2004-2012 for most sites but further techniques were introduced in 2004 to take advantage of disturbance permits for NR/MSK.

Main Techniques 1993-2003, also used 2004-2012 on many sites

Table 1 shows how a typical Honey-buzzard season progresses in Northumberland. Upland sites run 2-4 weeks later so fledging at some of these does not appear to be until mid-September, or even later.

Table 1: Timing of Breeding Season of Honey-buzzard in SW Northumberland

The timing of the season varies from year to year, necessitating corresponding adjustments in the fieldwork timing. The season in 2012 ran late throughout with display extending beyond mid-June, fledging starting in the last third of August and post-nuptial starting about a month later. Exact dates assigned to each stage this year are:

Display 1/5-18/6;

Sitting+Rearing 19/6-19/8;

Fledging 20/8-16/9;

Post-nuptial 17/9-25/10.

In practice defining such precise dates can be misleading over the whole study area. The dates may be reasonably accurate for lowland sites but at upland sites the season can run 2 or even 4 weeks later.

Using Table 1 as a guide, the strategy is ideally for each site, defined as a clump of trees, to:

• Find a pair displaying at the courtship stage.

• Observe some activity, however limited, in the Sitting and Rearing stages.

• Count the number of fledged young at the Fledging stage.

The full season is actually rather longer than the above:

February-April: visit wooded areas; locate Goshawk, Red Kite and other raptors; see changes in forests and woods and good vantage points.

Mid-October-early November: continue looking for late Honey-buzzard migrants.

mid-November-mid-February is break.

The strategy is an adaptation of that developed for Common Buzzards in their initial colonisation of Northumberland. Common Buzzards show the same basic pattern as Honey-buzzards with much activity at start and finish and almost complete invisibility at times during the incubation and rearing stages. The difference is that the Common Buzzard start and finish are much more drawn-out while the Honey-buzzard's are necessarily much more compressed because it is a long-distance migrant.

Common Buzzard Buteo buteo have courtship from February-early May, sitting from mid-April to mid-June, rearing from early June to late July, fledging from mid-July to early August and post-nuptial from late July to late October. They very rarely engage in full display in late May or early June and fledge about one month earlier than Honey-buzzards.

The standard criteria for breeding relevant to Honey-buzzard are based on those in the Atlas of Breeding Birds, 1976, by Sharrock. The ones actually used in Northumberland are shown in Table 2.

Table 2: Criteria for Breeding used for Honey-buzzard in Northumberland

It can be seen that finding recently fledged juveniles for most species confirms breeding. However, with a rare breeder further evidence is usually considered essential and recently can be subjective. There is extensive habitat for Honey-buzzards in the rest of Northumberland and in Scotland so it is possible that some juveniles seen in September are migrants. It is also possible that some adults seen in May and June are migrants. However, it seems most unlikely that adults will engage in territorial display on their way north. They may explore for trial sites within an area but wasting energy displaying at a site say 300km from their base while under the very tight time pressures imposed by the limited time for breeding seems very unlikely. Put another way, given the scarcity of the species, the chances, without some attempt at breeding, of the same group of trees in large woods being the focus of display in June, unobtrusive occupation in July and of weak-flying juveniles in early September, seem very low. Furthermore the increase in population observed is consistent with a successful local population.

We would consider it safe to consider a site as being in the CONFIRMED category if event 3 and either event 1 or 2 were satisfied for a particular site (defined as a clump of trees):

1. A pair showed territorial behaviour in the Courtship phase

2. Some indication was found for presence in the Sitting/Rearing phases

3. Recently fledged juveniles were seen in the Fledging phase.

Sites for which only events 1 or 2 are observed are in the probable category at best, though some may really be failed breeding attempts. Sites for which event 3 is the only one observed, are in the possible category if they are not known sites as the birds may have moved in from elsewhere and may possibly even be long-distance migrants. However, they are usually treated as Confirmed if the site is a known regular one. The history of a site is therefore taken into account in assigning a category.

The Dutch strategy for Honey-buzzard monitoring is very sophisticated (Bijlsma, 1997, p.28-30). We do photograph as many birds as possible but we do not identify individual birds on plumage. Also watching from tree-tops seems more appropriate to large forests in flat areas than to smaller woods in undulating country where many vantage points are available. Obviously we do put substantial time into this survey but living in the area means that local weather patterns can be seen as they develop. Ideal survey times are 09:30-13:30 (extending to 16:30 if a good day) in spring and the same but also as late as 17:30 in late summer and autumn. A fine day after several poor ones yields exceptional numbers. In 2002 some display was taking place in drizzle -- the birds just did not get much fine weather. After observation of the expected activity for the season at a site, that site is not usually visited again until the next stage of the season is reached.

Disturbance permit use in 2004-2012

Disturbance permits enabled us to get closer to the birds and search for nests. In 2004 one nest was found, the first in the county since 1841. In 2005 six selected sites were visited at intervals from ten days to 3 weeks, with interruptions for holidays and other absences. No trees were climbed to inspect nests and the birds seemed unaffected with 100% success at the visited sites. No site was visited for more than one hour and calls were recorded during this time opportunistically with a digital sound recorder and a hand-held tele-microphone. Some still photographs and video footage were also obtained opportunistically during the site visits. A nest was found at each of the six sites. In 2006 some winter work was done in additional sites with the aim of finding a total of ten nests in this season. This aim was achieved.

Finding Honey-buzzard nests is extremely difficult when inexperienced but becomes easier with practice. The first lesson learnt was that although the birds display around the tops of wooded hills, their nests are often at much lower altitude, usually in rough terrain near water (stream, ditch, pond). The birds are of course large so the nest must be near a ride or clearing to give them easy access. The nests are almost invariably in the lower part of the crown of tall trees, estimated typically at about 25m in 30m trees. The nests are not in commercial forestry in the mass production sense, but in stands of trees grown on towards maturity by wealthy private owners or conservation bodies. In oak or pine they are are not so difficult to see, once a precise area has been determined, but in another favoured tree, Norway Spruce, the nests are only visible from the ground with some effort, even when the precise area has been well established, because of the relatively dense crown structure. The liking for Norway Spruce is attributed by Bijlsma et al (1993, p.72) to the cover and screening provided by the crown which is particularly useful when both adults leave the nest area to forage, which inevitably occurs at times. In Northumberland the nests of Honey-buzzard appear very large from the ground and usually have sprays and leaves on the edge. The nests also increase in size through the season until mid-August as new material is added. Once the young have fledged the nests then appear to become smaller again quite quickly as maintenance ceases. Bijlsma et al (1993, p.72) considers that most Honey-buzzard nests can be identified at a single glance from the ground.

The effort in finding a nest in a wood may be high initially but there is a tendency to re-use the same nest for a few years so effort per nest in subsequent seasons declines. Common Buzzard may exceptionally nest within 100-200 metres of Honey-buzzards, although 300-500m is preferred. There is some interaction when the Honey-buzzards first arrive back but this soon lessens and the two species ignore each other. Hobbies will also nest close to Honey-buzzards and appear to mob them aggressively.

In the target area in 2012 13 sites were searched for nests with 100% success this year. Scots Pine (7 nests) is now clearly the most popular trees with Norway Spruce (3), Oak (2) and Douglas Fir (1) the only other type employed. Nests are much easier to find in Scots Pine and Oak than in Norway Spruce and Douglas Fir because of the structure of the crowns of the trees with for instance Scots Pine being open and Norway Spruce closed. In 2011 a series of photographs was taken from the ground of each nest in each site visit. Comparison of the photographs between visits showed a clean nest and an expansion of the structure between June/early July and late July/August confirming that the nest was in use. This comparison supports the nests being assigned to Honey-buzzard as a species because it is exactly what would be expected with a tidy late nesting species. Common Buzzard nests always appear very much more used near fledging in early July and are indeed already starting to decline in structure at this point. The material is there also for 2012 but has not yet been analysed.

Survey Effort

Vast. 15-20 hours a week over the 25 week season in on-site fieldwork. With some breaks for holidays, perhaps 300-400 hours a year from early May to early October.

Comparison with Work in Scotland/Britain

Hardey et al (2006 p.66-71) in their guide to raptor survey and monitoring, make a number of statements and suggestions about the monitoring of Honey-buzzards. Much fits in well with experience in Northumberland, but it is worthwhile highlighting a few differences:

1. Very few sites are ever occupied in late April in Northumberland (just one to date).

2. Territorial display does not occur from mid-June to early August in Northumberland with breeding birds sitting tight and adopting a very low profile. Non-breeding birds have occasionally been observed displaying in July.

3. Three visits, not four, are made to confirm occupancy in Northumberland. Visits 2 and 3 (June and July) are amalgamated into one in Northumberland. However, more visits are made in Northumberland to sites where the intention is to find the active nest using the disturbance permit.

4. Evidence of breeding categories are similar in that both treat recently fledged young as confirmed (though see above for corollary in Northumberland). Nest with eggs or young is represented by occupied nest (ON) in Northumberland. The other category for confirmed breeding in Northumberland of carrying food (FY), treated as probable in Hardey et al (2006), has been very rarely used in Northumberland to confirm breeding. Nests that fail in Northumberland will most likely be recorded as possible/probable rather than confirmed breeding but failed.

As a result of this comparison, the category FY has been moved in Northumberland from 2007 to match Hardey's definition of the probable breeding category. The treatment of calls is an area where some advance perhaps could be made nationally in future. A number of the calls such as anger, alarm, wailing and ticking surely confirm breeding but of course there is usually other evidence when the nest site has been penetrated sufficiently to hear such calls.

Disturbance permit use in 2012

Two visits were made to each of the 13 sites selected, the first from mid-June to mid-July and the second from early-August to early September. After some experimentation over the years this timing appears to be optimal as it avoids disturbance when the birds are settling in but is at an active point, egg hatching for first, young fledging for second, so that positive results can be obtained.

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