Home range, habitat use
and diet of Honeybuzzards during thebreeding season
Fridtjof Ziesemer and Bernd-Ulrich Meyburg
Abstract Four adult male Honey-buzzards Pernis apivorus were fitted with GPS
satellite transmitters in northern Germany. The tags were deployed during thenestling period and the birds followed until they started their autumn migration.
For one male, data were also collected throughout the following breeding season.
The four birds occupied home ranges that varied between 13.5 and 25.8 km². The
birds spent most of their time in woodland and apparently found most of theirfood there: of 35 wasp and two bumblebee nests that were found, 78% were inwoodland. In all, 99% of the locations received from the four males were within aradius of 4 km of the nest. The birds roosted at different sites, some of whichwere close to the nest, but sometimes close to wasp nests that had not been fully
exploited. As the young developed, the males visited new areas for foraging, andspent more time farther from the nest. The most frequently recorded food item
was the Common Wasp Vespula vulgaris. Possible effects of the recent changes
in the occurrence patterns of key wasp species, especially the German Wasp
V. germanica, are discussed.

T

he generally secretive Honey-buzzard
Pernis apivorus is a difficult species tomonitor effectively in its European
breeding areas. In the past decade or so, theEuropean population was estimated at
110,000–160,000 (BirdLife International
2004) or approximately 130,000 breedingpairs (Mebs & Schmidt 2014), although population estimates should be viewed withcaution. In Europe as a whole, the population
is believed to be stable (BirdLife International
2004), yet an analysis of breeding populations, productivity and survival rates provides clear evidence of population declines insome areas, including parts of its range innorthwest Europe (Bijlsma et al. 2012).
The factors influencing this decline could
operate on the breeding grounds, on migration
and/or in the birds’ winter quarters, in West
and Central Africa, where forest destruction© British Birds 108 • August 2015 • 467– 481

continues at a rapid rate (Martin 1991; Oates
1999). Continuous tracking of a number ofindividual birds throughout the year may help
to identify problems and determine where they
are occurring. Between 2001 and 2011, we
fitted solar-powered satellite transmitters (platform transmitter terminals, or PTTs) ofvarious types, weighing 18–22 g, to 12 adult
Honey-buzzards in Germany. (For more information on the technique of satellite tracking,see Meyburg & Fuller (2007) and Meyburg &Meyburg (2007, 2009, 2013).) From 2009
onwards, we were able to use transmitters thatgave precise GPS fixes, and these provided thebulk of the information reported here, which
relates to the breeding season only.

Study area and methods
Our studies were carried out in eastern
Schleswig-Holstein (the most northerly
467

Ziesemer & Meyburg
Table 1. Number of fixes per day for thetagged male Honey-buzzards.
Argos transmitter
ID numberfixes/day
range
mean

male 1

95770

8–17

12.2

male 2

95771

10–19

15.4

male 3 (2010)

52033

0–9

2.1

male 3 (2011)

52033

0–13

3.8

male 4

68561

0–19

2.9

to be collected from females. However, sufficient data were obtained from the four males
to measure various attributes of their homerange and behaviour. Data were collectedfrom the beginning of the day after the transmitters were fitted until the birds’ departurefrom the breeding area.
The transmitters used in 2009 (birds 1 and
2) broadcast two-dimensional (2D) coordinates. In 2010 and 2011, the three-dimensional (3D) transmitters fitted to birds 3 and4 also provided information on height above
sea level (asl) as well as flight speed anddirection. Because 3D transmitters require
more power than 2D transmitters, they provided markedly fewer fixes when the bird was
not in direct sunlight (table 1). According to
the manufacturers, Microwave Telemetry,these tags are accurate to within ± 18 m forlongitude and latitude, ± 22 m for height andFridtjof Ziesemer

German federal state), an undulating, agricultural landscape with heights between 20
and 80 m asl. Most of the farmland is arable,
but there is some grassland, managed by a
combination of grazing and silage. The fields,on the mainly sandy/clay soils, are often separated by banked hedgerows (an earth bank,with hedgerow planted along the top) interspersed with numerous patches of woodland.
In a rectangular area of 630 km² that encompassed the home ranges of all the Honeybuzzards studied (mid-point 54.22°N
10.43°E), the proportion of woodland was
15% while the total length of banked
hedgerows (as an indicator of the density ofboundary lines) was 2,945 km, or 4.7
km/km². Most of the woodland is managed
for timber and deciduous trees (notably
Beech Fagus sylvatica) predominate; in thearea of 630 km² referred to above, 47% of thewoodland is mixed, 40% is deciduous and
13% coniferous.
We fitted seven adult Honey-buzzards(three females and four males) with solarpowered GPS PTTs between 2009 and 2011.
All birds were captured close to the nest
during the nestling stage. Since the females
spend a great deal of time near the nest whilebrooding small nestlings and in generalspend little time in the sun during thebreeding cycle, the solar cells did not provide
sufficient charge for a usable amount of data

262. A view over the Plön region of Schleswig-Holstein, Germany, in August 2009 – part of thehome range of Honey-buzzard Pernis apivorus male no. 1 in this study.
468

British Birds 108 • August 2015 • 467– 481

Fridtjof Ziesemer

Home range, habitat use and diet of breeding Honey-buzzards

262. A typical field boundary in Schleswig-Holstein, comprising a banked hedgerow where a wasp
nest has been excavated by a Honey-buzzard; August 2009.

± 1 km/h for speed when this exceeds 40
km/h.
Fixes from the birds’ daytime activity
phase were plotted to calculate the homerange and other parameters. The local timesof sunrise and sunset were used to determine
the overnight roost sites. If the bird’s firstmorning movement was more than 80 mfrom the roost, the start of the daily activity
phase was assumed. Conversely, the first fix
from the overnight roost was taken to represent the end of the daily activity phase.
Data from the nestling period are available
for all birds. Male 3 returned the year after it
was tagged, again bred successfully at thesame nest and was tracked throughout thebreeding period in this year.
Various models were tested to provide themost accurate representation of home range.
Home ranges can be represented as boundaries of the fix locations (Minimum Convex
Polygon, or MCP; Kenward 2001). An MCP
is the smallest polygon with outer angles>180º, which encloses a defined percentage
of all fixes. In order to exclude occasional
excursions to distant areas, which would
greatly increase the size of the MCP, it is standard practice to include only the closest 95%
of fixes in the calculation (MCP 95). Some
British Birds 108 • August 2015 • 467– 481

authors also calculate the MCP 80, to illustrate the parts of the home range which areused most regularly. MCPs thus comprise acluster of fixes, but do not tell us how thosefixes are distributed within the home range.
The most useful model proved to be theKernel Density Estimation (KDE), which wasused to map the utilisation distribution. This
contour-based method is often used formapping home ranges and evaluates utilisation distribution by generating high-density
centres based on contour lines (Bowman
1985; Worton 1989). The dots represent the
GPS fixes, the lines the kernel isopleths. The
kernel isopleth lines mark the probability ofoccurrence: from 95%, 90%, 80%, 70% andso on down to 10% (and so the outside line
encompasses 95% of the probable locations
visited). Thus, the highest utilisation density
is in the centre, decreasing towards theperiphery.
We evaluated the GPS data with the software package GIS ArcView 3.2a. In addition,
we used the Google Earth satellite photoprogram with diverse supplements foranalysis. To evaluate the GPS fixes, the homerange extension for ArcView© from Rodgers& Carr (1998) and the home range tools for
ArcGis© from Rodgers et al. (2007) were469

Ziesemer & Meyburgused. These programs also calculate MCP.
For MCP 95 and MCP 80, the Floating
Amean method (proximity to recalculated
mean of selected fixes) was used. Thereby thearithmetic mean of all fixes is calculated, thenthe most distant point determined anddeleted, and once again the arithmetic meanof all remaining fixes established. This
process is repeated until only 95% or 80% of
the fixes remain. Google Earth Pro Version
7.1.2.2041 was used to create the maps,
which are published on the basis of Google
Order ID 577948 (licence holder B-U.
Meyburg).

Here, we present the size of the homeranges as 95% KDE alongside the MCP that
contains 80%, 95% or 100% of all fixes, inorder to provide easier comparison with theresults of other authors.
The extent of woodland within the birds’
home ranges was assessed using the countryside information system of the Schleswig-Holstein State Office for Agriculture,
Environment and Rural Affairs and maps produced by the Schleswig-Holstein State Survey
Agency 2009. Where clusters of fixes indicatedexcavated wasps’ nests, these were searched
for, mainly within the following few days.

Table 2. Brood development and nesting phenology of the tagged Honey-buzzards.

male 1male 2male 3 (2010)
male 3 (2011)
male 4

GPS data recorded
20.07–26.08.2009
19.07–29.08.2009
08.08–24.08.2010
19.05–13.08.2011
16.07–18.08.2011

chick ringing datadate
age of first chick
22 July 09 19 days
22 July 09 20 days
25 July 10 21 days
30 July 11 35 days
30 July 11 25 days

derived phenology
first-egg date first chick hatched
1 June3 July31 May2 July2 June4 July22 May25 June3 June5 JulyTable 3. Size of home ranges (km²); see text for explanation of different measures used to define
home range.
male 1male 2male 3 (2010)
male 3 (2011)
male 4

KDE 95
17.3
25.8
–
13.6
13.5

MCP 80
9.7
10.1
7.0
2.8
3.1

MCP 95
12.3
17.4
14.0
6.3
6.4

MCP 100
28.7
39.8
14.3
13.2
9.2

no. of fixes
456
637
35
332
100

date range
20.07–26.08.2009
19.07–29.08.2009
08.08–24.08.2010
19.05–13.08.2011
16.07–18.08.2011

Table 4. The number of fixes in woodland and in other areas.

male 1male 2male 3 (2010)
male 3 (2011)
male 4

woodlandno.

%non-woodland
no.

total
no.

387
558
24
367
81

85
88
69
94
81

69
79
11
25
19

456
637
35
392
100

Table 5. Woodland area (km²) and proportion of woodland (%) in the home ranges.
male 1male 2male 3 (2010)
male 3 (2011)
male 4470

KDE 95
2.4
5.4
–
3.0
1.8

%
13.9
21.1
22.2
13.1

MCP 80
2.0
2.4
3.0
2.0
0.9

%
20.5
23.5
43.5
71.2
28

MCP 95
2.4
3.9
3.4
3.8
1.4

%
19.2
22.4
24.3
60.7
21.2

MCP 100
3.8
7.6
3.4
4.7
1.5

%
13.4
19.2
23.9
35.9
16.7

British Birds 108 • August 2015 • 467– 481

Home range, habitat use and diet of breeding Honey-buzzards
Results
Breeding data
Basic information on brooddevelopment and the period
during which the GPS fixes
were recorded are shown intable 2. The age of thechicks at the time of ringing
was determined using the
growth curve in Bijlsma(1997). The calculation of
the first-egg date andhatching of the first chick isbased on an assumed incubation period of 33 days
from laying of the first egg,
and a laying interval of twodays (van Manen et al.
2011).

Home range andhabitat selection
1 km
Fig. 1. Home range of Honey-buzzard male 1 (95770), on the city
limits of Plön (KDE; the outside line encompasses 95% of theprobable locations visited, the inner lines represent 90%, 80% and soon down to 10%; see text for details). Dots: 456 GPS fixes between
20th July and 26th August 2009; red star denotes breeding site.

1 km

Fig. 2. Home range of Honey-buzzard male 2 (95771), to the westof the Selenter See (KDE). Dots: 637 GPS fixes between 19th Julyand 29th August 2009.
British Birds 108 • August 2015 • 467– 481

The sizes of the different
homerangesvariedbetween 13.5 and 25.8 km²(KDE 95%) (table 3, figs. 1–4). By far the greatest
number of fixes (69–94%)
were from woodland areas(table 4). This is much morethan expected based on the
proportion of woodland
within the home ranges. For
male 3, which nested in awoodland of 5 km², 61% of
the home range was woodland, but the other threemales had only around 20%
of woodland within theirhome ranges (MCP 95;
table 5). The male Honeybuzzards clearly preferred
to remain in the woods,
although they occupied alandscape where the woodland is highly fragmented.
The absolute size of thetotal area of woodland in
the home range of the four
Honey-buzzards varied
between 1.8 and 5.4 km²(KDE 95%) and 1.4 to 3.9
km² (MCP 95%; table 5).
471

Ziesemer & Meyburg
Diet
A cluster of fixes can suggest that a Honeybuzzard has exploited a food source at a particular location over several hours or evendays. However, such food sources can be
identified only if visible remains are left
behind. The easiest of the regularly exploitedfood sources to find are the excavated nestsof ground-dwelling wasps. With three exceptions (one bumblebee Bombus and two
Common Wasp Vespula vulgaris nests), allfinds were in July and August. Additionally,
during fieldwork, ten Common Wasp andtwo bumblebee nests were found by chance.
One bumblebee and one wasp nest had been
exploited by Honey-buzzards while two wasp
nests showed scratches but
remained unharmed.
In total, 29 of 37 (78%)
excavated wasp and bumblebee nests were found inwoodland, four at theedges of pasture land (e.g.
along fences, ditch lines),
three in banked hedgerows
and one in a harvested
rape field, 5 m from ahedgerow (figs. 5–6, table6).

Temporal and spatial
use of home range

1 km

Fig. 3. Home range of Honey-buzzard male 3 (52033), near Eutin.
Dots: 35 GPS fixes between 8th and 24th August 2010 (yellow) and
332 fixes between 19th May and 13th August 2011 (red, plus KDE
contours).

In total, 1,609 of the 1,620
fixes (99%) from the fourmales were within 4 km of
the nest, including all
overnight roosts. Male 1
flew up to 6.2 km from thenest, the greatest distancerecorded. In general,
however, the proportion offixes for all four males
decreased with distancefrom the nest (fig. 7). Birds
were most often found in

1 km

Fig. 4. Home range of Honey-buzzard male 4 (68561), near Malente (KDE). Dots: 100 GPS fixes
between 16th July and 18th August 2011. Red star denotes breeding site.
472

British Birds 108 • August 2015 • 467– 481

Home range, habitat use and diet of breeding Honey-buzzards
to brood small chicks, at times
when the female was away fromthe nest, was assumed to be from26th June to 10th July. Male 3 left
bumblebee
the breeding area on 13th August,Bombuswhen the first chick was about 49
0days old, and the day after the0
second chick had been killed by a0
Northern Goshawk Accipiter1
gentilis.
1
During the pre-hatching2
period, almost half of the fixes
from male 3 were from the nest and its
immediate vicinity (40% within an 80-m
radius, 47% within a 250-m radius aroundthe nest). During the period in which thechicks had to be brooded, this proportion
hardly changed (42% and 45% respectively).
Thereafter, this male was more wide-ranging
and active up to 3 km from the nest, so 23%
and 28% of fixes were within 80 m and 250
m of the nest respectively (fig. 9).
As the breeding season progressed, thefocus of the birds’ activity shifted and theyspent more time farther away from the nest
(fig. 10). The most likely explanation for thispattern is the increased demand for food by
growing nestlings, requiring the exploitationof more distant resources. Larger young
require less protection from the adults andcan be left for longer periods.
The nestling period has been reported as

Table 6. Wasp and bumblebee nests excavated by tagged
Honey-buzzards.
Common Wasp
Vespula vulgaris
male 110
male 211
male 3 (2010)
1
male 3 (2011)
6
male 4
5
Total
33

German Wasp
V. germanica
1
1
0
0
0
2

British Birds 108 • August 2015 • 467– 481

Fridtjof Ziesemer

the woodland where their nest was located,with other concentrations of fixes in thenearest neighbouring woods.
At night, the distribution of fixes differedamong individuals. Whereas male 1 often
roosted close to the nest (within 250 m),
males 2 and 3 seldom did so, instead roostingat various locations within their hunting area(but most commonly within 1 km of thenest; fig. 8). Occasionally, males 1 and 2
roosted close to wasp nests that had not fully
been exploited. Only five night-roost fixes
were recorded for male 4, and in 2010 only
one night-roost fix for male 3, so that anevaluation of roosting behaviour in thesecases was not possible.
For male 3, we were able to study the distances flown from the nest during all stagesof the breeding season in 2011. This individual arrived in the breeding area on 19th
May that year andon the morning of
20th May it wasobserved repeatedly chasing one ormore rival males
and flying with afemale (similar to,and presumed tobe the same as, its
mate from 2010).
The laying andincubation period(calculated backfrom the ringing
dates of the young)began on 22nd
May and ended
on 25th June. The
periodduring 263. An excavated wasp nest at the edge of a ditch in the study area;
which the male had August 2009.

473

Ziesemer & Meyburg

Fig. 5. Wasp nests exploited by Honey-buzzard male 1 (95770): ten
Common Wasp and one German Wasp (black star) nests, from 20th
July to 26th August 2009. Red star denotes breeding site.

37–42 days in Honey-buzzards and the post-fledging
period (the time between
fledging and the young
becoming independent) as
5–25 days (Bijlsma 2009).
Of the three females andfour males tracked by us,
the first adult of each pairleft the breeding area when
the first chick was 44–49
days old, while theremaining adult left when
the first chick was 46–58
days old. In two pairs it
was the female thatdeparted first. However, in
two pairs observed in 1993
and 1995 respectively, one
female and one male were
the first to leave (Ziesemer1997).

Diurnal activity
patterns

Fig. 6. Wasp nests exploited by Honey-buzzard male 2 (95771): 11
Common Wasp and one German Wasp (black star) nests, from 19th
July to 29th August 2009. Red star denotes breeding site.
474

As a rule, adult Honeybuzzards were alreadyactive at first light. On afew days they were morethan 80 m from theirovernight roost more thanhalf an hour before
sunrise, e.g. male 1 on sixof 16 days and male 2 onfour of 29 days. In contrast, male 3 (2011) was
still at its overnight roostat sunrise on the 11 days
for which data are available. Longer distances weresometimes flown early inthe day. For example, on
8th August 2009, male 2
was at the nest 42 minutes
before sunrise, after having
spent the night 2 km away.
Hourly fixes were too
imprecise to record thestart and end of diurnal
activity accurately. It wasnoticeable, however, thatthe birds became active
early, often around first

British Birds 108 • August 2015 • 467– 481

Home range, habitat use and diet of breeding Honey-buzzards
male 1 (95770)% GPS fixes (n = 377)

40
30
20
10

4750

5250

5750

6250

5250

5750

6250

4250

4750

3750

3250

2750

2250

1750

750

1250

250

0
distance to nest (m)male 2 (95771)% GPS fixes (n = 523)

40
30
20
10

4250

3750

3250

2750

2250

1750

1250

750

250

0

light, although not on dark and rainy days. In
addition, when a bird brooded overnight into
the daylight hours, it left the nest only whenrelieved by its partner. It was also clear thatbirds ceased to be active towards sunset.
Three males studied in the Netherlands
ended their diurnal activity on average 28
minutes before sunset (van Diermen et al.
2009).
Honey-buzzards search for the nests ofwasps and bumblebees by following theirflight movements (Glutz von Blotzheim et al.
1971; Högstedt 1976). For example, theCommon Wasp starts flying very early in themorning. At first, worker wasps that havespent the night outside the nest return, whilesoon after others begin to leave the nest.
Thus on average, and depending on the timeof year, activity can be higher in the early

distance to nest (m)75% nights (n = 33)

30
20

50

25

3250

3500
4000

3000

3750

2750

2500

2250

2000

1750

1500

1250

750

1000

500

6250

5750

5250

4750

4250

3750

3250

2750

2250

1750

1250

750

0
0

250

10
250

% GPS fixes (n = 34)

male 1 (95770)

male 3 (52033) – 201040

distance to nest (m)distance to nest (m)male 2 (95771)

75

male 3 (52033) – 2011

3500

3250

3000

2750

2500

2250

2000

1750

1500

1250

1000

distance to nest (m)

6250

5750

5250

4750

4250

3750

3250

2750

2250

1750

1250

750

0

0

750

10

25

500

20

50

250

% nights (n = 40)

30

250

% GPS fixes (n = 317)

40

distance to nest (m)male 3 (52033) – 201140

male 4 (68561)% nights (n = 14)

30
20

30
20
10

10
0
6250

5750

5250

4750

4250

3750

3250

2750

2250

1750

1250

0250
750

0

250

% GPS fixes (n = 317)

40

distance to nest (m)Fig. 7. Distance of daytime fixes from the nest.
British Birds 108 • August 2015 • 467– 481

0500

0750

1000

1250

1500

1750

distance to nest (m)Fig. 8. Distance of overnight fixes from thenest, for males 1, 2 and 3.
475

Ziesemer & Meyburg

40
30
20

3250

3000

2750

3250

3000

2750

0

25.8

23.8

1
0

distance to nest (m)Fig. 9. The spatial distribution of daily fixes ofmale 3 (52033) in 2011, plotted in relation to
the nest site, during three different phases ofthe breeding cycle.

male 4 (68561); n = 91

3
2

17.8

15.8

13.7

11.8

9.8

7.8

30.7

28.7

26.7

24.7

22.7

0

20.7

1

18.7

3250

3000

2750

2500

2250

2000

1750

1250

1500

1000

5
750

21.8

2

16.7

10

mean distance to nest (km)

20
15

250

19.8

male 3 (52033) – 2011; n = 317

3

date

feeding chicks >15 days old(11th July – 13th August)500% GPS-fixes (n =106)

17.8

1

distance to nest (m)

476

15.8

2

5.8

2500

2250

2000

1750

1500

1250

1000

750

500

10

0

13.8

3

19.5
22.5
30.5
2.6
5.6
11.6
15.6
21.6
24.6
27.6
2.7
7.7
10.7
15.7
20.7
27.7
31.7
3.8
6.8
10.8

20

mean distance to nest (km)

30

250

% GPS-fixes (n = 55)

brooding small chicks(26th June – 10th July)

25

9.8

male 2 (95771); n = 523

4

date

40

0

11.8

date

distance to nest (m)

50

7.8

5.8

3.8

1.8

30.7

28.7

26.7

24.7

22.7

0

20.7

1

3.8

2500

2250

2000

1750

1500

1250

750

1000

0

500

10

2

1.8

50

male 1 (95770); n = 377
3

19.7
21.7
23.7
25.7
27.7
29.7
31.7
2.8
4.8
6.8
8.8
10.8
12.8
14.8
16.8
18.8
20.8
22.8
24.8
26.8
28.8

laying and incubation period(19th May – 25th June)250% GPS-fixes (n = 156)

The home range (KDE 95%) of three of thefour males was within the range 13.5–17.3

mean distance to nest (km)Discussion
Size of the home ranges

km², while male 2 had a markedly larger
home range, of 25.8 km². Male 2 foraged inwoodlands to the west and north of its nest,
which are known to regularly support
breeding Honey-buzzards, although we do
not know whether these territories were
occupied in the study year. Home ranges ofmean distance to nest (km)morning than later in the day. Thereafter,
activity remains more or less constantthrough the day, but can tail off towards
evening; the start and end of activity is determined primarily by whether there is enoughlight to navigate by. Other wasp species
appear to have a similar activity pattern, andhornets are known to be active at night(Spradbery 1973; Matsuura & Yamane 1990;
Archer 2005, 2012). It remains unclear why
Honey-buzzards tend to curtail their activities earlier in the day than some of their key
prey species.

dateFig. 10. Mean distance from the nest of fixes
during each day as the breeding season
progresses (all fixes plotted, from 30 minutes
before sunrise to 30 minutes after sunset).
British Birds 108 • August 2015 • 467– 481

males can overlap (van Manen et al. 2011;
Diet
pers. obs.), but the frequency with which
After their arrival in the breeding area,
male 2 visited these woods may indicate that
Honey-buzzards initially feed mainly onneighbouring territories were not occupied
amphibians, young birds and (less frein 2009 and that, compared with the otherquently) reptiles. As colonies of social wasp
males, this individual was able to make use of
species develop, Honey-buzzards switch toa larger area than usual without encountering
wasp larvae as their staple diet (Holsteinother breeding birds.
1944; Itämies & Mikkola 1972; van Manen et
The 15 males studied by van Manen et al.
al. 2011).
(2011) in the Veluwe area of the Netherlands
Social wasps (Vespidae) pursue one of two
had home ranges (KDE 95%) of 5.7–13.1
life strategies. In the first, they develop small
km² with a mean of 9.6 km², thus smallercolonies with a lifespan of 3–4 months, inthan those in Schleswig-Holstein. The pronests that are free-hanging in vegetation or
portion of woodland in the Veluwe area is, atbuilt close to the surface of the soil, and49%, considerably greater than the 15–20%
which benefit from direct warmth from thewoodland cover in the Schleswig-Holsteinsun. The Red Wasp Vespula rufa and thestudy area. Since wasp nests are found primalong-faced wasps Dolichovespula spp. pursue
rily in woodland, it is likely that the Veluwe
this strategy. The alternative strategy, folHoney-buzzards were able to find sufficient
lowed by the German Wasp V. germanica andfood within a smaller area than in Schleswigthe Common Wasp (Archer 2012), is to
Holstein. The density of wasp nests is known
develop large colonies that can live for 5–6
to be one of the factors affecting the size ofmonths in underground nests, where they are
the home range (Gamauf 1999).
insulated against cool weather in autumn.
A greater proportion of woodland does
Although all wasp species begin to develop
not automatically result in a smaller hometheir colonies at about the same time, in mid
range, however. The home ranges of six male
May, those using the first strategy can comHoney-buzzards in the southern part of theplete their colony-building as early as July,
Netherlands, where the study areas had 28–
weeks before the latter reach their peak devel33% woodland cover, were 13.8–45 km²
opment. The timing of the German and(MCP 95%) during the second half of theCommon Wasp colonies fits in better with
nestling period, larger than in Schleswig-Holthe food requirements of young Honeystein during theequivalent period(6.3–17.4 km²; vanDiermen et al. 2013).
The authors noted adeclining attachment
to woodland of fourof the six males
through this period,and found that traps
set out in August to
determine
wasp
density caught morewasps outside than
within woodland.
The large homeranges in this wellwooded study area
may reflect the deple- 264. An excavated wasp nest in deciduous woodland in the study area;
July 2011. This shows the characteristic remains of a wasp nest that hastion of wasp nests been exploited by a Honey-buzzard, with empty but intact comb fragments
within woodland – Honey-buzzards eat the individual grubs, whereas mammals would chew
during the year.
the comb.
British Birds 108 • August 2015 • 467– 481

477

Fridtjof Ziesemer

Home range, habitat use and diet of breeding Honey-buzzards

Torsten Pröhl /fokus-natur.deZiesemer & Meyburg265. Adult male Honey-buzzard Pernis apivorus carrying wasp comb; Germany, August 2014.

buzzards. As the colonies of these species also
contain more larvae than any of the otherspecies, they tend to dominate the diet ofolder chicks. Hornets Vespa crabro also
pursue the second life strategy. However,since their nests are mostly built in tree holes,
they are less accessible to Honey-buzzards,
unless built in rotting soft wood (vanDiermen et al. 2013; Harmsen & Bijlsma
2014).
Based on satellite fixes, 33 Common Wasp,
two German Wasp and two bumblebee nests
were located and recorded as Honey-buzzard
prey in this study. In 1993–95, Ziesemer(1997) recorded more varied prey of fourmale Honey-buzzards, which included 43
Common Wasp, nine German Wasp and 13
nests of four other wasp and bumblebee
species. This predominance of the two wasp
species with the largest colonies (especially
Common Wasp) is probably due not only tothe fact that their nests offer more food, butalso to the research method used. The probability of observers locating food remains
increases with the conspicuousness of theremains left behind. The exploitation of asmall hanging wasps’ nest in a bush leaves
few visible remains, while large wasps’ nests
excavated from the soil are most likely to befound by human observers. Since, in ourstudy, the Honey-buzzards were not fittedwith transmitters until July/August, the478

chance of establishing Dolichovespula species
and V. rufa as prey species were reduced. In
addition, the timing of transmitter broadcasts (one fix every hour, at best), meant thatthe likelihood of observers finding a nest was
greater if a Honey-buzzard had been occupied with it for a number of hours. With lessthan one fix per hour, as was often the case,the probability of finding any food remains
at all was greatly reduced. Yet although thetechnology did not permit a representativeinterpretation of prey choice, it did show thatthe Honey-buzzards located large wasps’
nests, the main source of food for rearing
their young, above all in woodland (78%)
and in the edge habitats of the agriculturallandscape.
It is not clear why the German Wasp is sounder-represented as prey compared with theCommon Wasp. Both species occur widely inEurope where, according to Gusenleitner(1975), Common prefers cooler regions than
German. Both species are generally common
in Schleswig-Holstein, though they differ intheir habitat requirements. Common occurs
both in woodland and elsewhere, whereas theGerman Wasp tends to avoid woodland(Dvorak 2007). Honey-buzzards will seek
and locate wasp nests both within andoutside woodland, however, so differences inhabitat preferences of the two wasp species
are not necessarily the reason for the marked
British Birds 108 • August 2015 • 467– 481

Home range, habitat use and diet of breeding Honey-buzzards
this study because of the interval between
fixes (one hour or longer). Although males
search for food in all parts of their homerange, they tend to actively defend their territory within a radius of 2 km of the nest
(Gamauf 1988; Ziesemer 1997). In good
weather conditions, they can spend a great
deal of time in the air. Flights to more distantlocations are primarily foraging trips, and we
attributed all fixes within a radius of 80 m ofthe nest to the immediate care of the brood(nest-building, breeding, feeding, on watch,etc.).
In Honey-buzzards, both sexes contributeto incubation and brooding. There are,however, differences in the division of tasks
between the partners (e.g. Holstein 1944,
Roberts & Law 2014). The proportion of fixes
within 80 m of the nest recorded for male 3
in 2011 was 40% during egg-laying and incubation, 42% when the nestlings were small,but just 23% when the nestlings were large
enough to be left unattended. This corresponds fairly well to the values recorded forseveral males in the Netherlands by van
Manen et al. (2011): around 40% until the
young hatched, 30–40% in the period whensmall nestlings had to be kept warm andabout 10% subsequently.
The distances that males travelled awayfrom the nest were also similar in bothstudies. In this study, 99% of all fixes were
within a radius of 4 km of the nest, whereas
the equivalent figure in van Manen’s study

Torsten Pröhl /fokus-natur.devariation in their occurrence in the prey list.
A noticeable decline in the population ofGerman Wasps was reported in England in
the period 1970–2000 (Archer 2001), and isalso suspected to have occurred in Germany(Witt 2010).
As well as a possible population decline, achange in the seasonal occurrence of theGerman Wasp is a potential reason for its
under-representation in prey. Tryjanowski etal. (2010) and Visser & Both (2005) point to
the fact that some wasp species, including
German Wasp, have markedly advanced theirflight times in association with climate
warming. Bijlsma (2012a) established that,for several years now, German Wasps had
reached the peak of their activity as early as
mid July, and that nests could be largely
abandoned by the beginning of August. The
reduction in availability of such an important
prey item, especially at the time of greatest
demand for food, could affect Honeybuzzard breeding success and further study
would be worthwhile.
The density of all wasps’ nests combined –and therefore the Honey-buzzard’s mainfood supply – is subject to strong fluctuation.
According to a frequently cited example fromEngland (the Royal Horticultural Society
gardens at Wisley, in Surrey, 1921–1949), thiscan vary by a factor of about 42 (Archer2012). Bijlsma (2012b) found a similar rangeof fluctuation (factor of 40) in the Netherlands during the period 1974–2011. To date,however, only wasp
availability in extreme
years has had a noticeable effect on thebreeding success of
Honey-buzzards.
Seemingly, in years
when wasps are scarce,
sufficient alternative
prey, such as frogs andyoung birds, was available.

Distance fromthe nest
It is not possible todetermine the finedetail of the tagged
birds’ movements in

266. Male and female Honey-buzzards Pernis apivorus at the nest site,with small chick; the male bird (left) has arrived with a piece of wasp
comb; Germany, 13th July 2014.

British Birds 108 • August 2015 • 467– 481

479

Ziesemer & Meyburg
was 94%. During the course of the breeding
season, the Dutch males extended theirsearch for food from 1.5 to 3 km from thenest, on average. This corresponds withflights of increasing distance in SchleswigHolstein (figs. 9 & 10), although it is not possible to attribute these to particular activities.
In the same way, van Manen et al. (2011)
found that most of the males roosted at nightat different locations, on some occasions at
wasp nests that had not yet been exploited.
Such ‘guarding’ of exposed wasp nests reflects
the fact that they are otherwise easily
exploited by other Honey-buzzards(Ziesemer 1997; van Diermen pers. comm.).
In the Netherlands, it was found thatfemales regularly foraged more than 10 km
from the nest (van Manen et al. 2011),
whereas males remained closer to the nest
site, as in our study. During these longer
flights, females specifically visited individual,
food-rich locations. In this way, their homerange could be regarded as several, widely
separated areas that, taken together (based on
KDE 95% for foraging positions), could beeven smaller than the home range of themales. Similar flights have also been recordedin Schleswig-Holstein; for example, one
female traversed several other Honeybuzzard territories, about 1–2 days before thefirst chick hatched (Ziesemer 1997). This isunusually early, as in most years females will
undertake long foraging flights only once thechicks are old enough to maintain their bodytemperature unaided (van Diermen pers.
comm.). Later, when the chicks are wellgrown (four weeks or more), females frequently visit distant foraging areas, as far
away as 124 km from the nest and for one orseveral days, before subsequently returning,sometimes to feed their young (van Diermen
et al. 2013).

Habitat
The fixes of all four males in our study
showed a clear preference for woodland, evenafter taking into account the fact that nests
are situated within this habitat. This, we
believe, relates to the biology of social wasps
and bumblebees, which build their nests
underground as well as in trees and bushes.
Ground nests, which are frequently built inabandoned mouse holes, can be constructed
480

only in unbroken soil. Thus arable land,
which is tilled annually, is usually avoided,
while grassland is suitable only to a limited
extent, owing to the trampling of livestockand disturbance of the soil by heavymachinery. Wasp nests in human settlements
can be exploited only if there is little humandisturbance, for example in the large gardens
on the outskirts of small settlements(Ziesemer 1997; van Manen et al. 2011).
Wasps’ nests are therefore predominantly
accessible to Honey-buzzards in woodland,
as well as around the margins of the agricultural land, particularly in banked hedgerows
but also verges and embankments, etc. The
significance of woodland was also demonstrated in this study by the fact that 78% of
the exploited wasp and bumblebee nests wefound were in this habitat.
Acknowledgments
We are grateful to the various foresters andlandowners in the study area for permission to conduct
fieldwork in their woods. The Schleswig-Holstein State
Office for Agriculture, Environment and Rural Affairs
issued the permits for marking the Honey-buzzards.
Christiane Meyburg was responsible for the computer
analysis, interpreting the original data received via
Argos, as well as calculating the home range sizes andpreparing the maps. Paul Howey, president and ownerof Microwave Telemetry, provided valuable assistanceand information and ensured delivery of transmitters at
short notice. Günter Kurz and Hans Dieter Martens
provided valuable help with the capture of the birds.
Wolfgang Petersen contributed data on landscapefeatures. Thomas Keller gave advice on the statisticaltreatment of data, while most of the translation into
English was carried out by David Conlin. Finally, we
thank Ian Newton and five anonymous referees forreviewing the paper.
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Dr Fridtjof Ziesemer, Zum Brook 16, 24238 Lammershagen, Germany;e-mail f.ziesemer-corax@t-online.de
Prof. Dr Bernd-Ulrich Meyburg, Wangenheimstr. 48, 14193 Berlin, Germany;e-mail BUMeyburg@aol.com
Fridtjof Ziesemer completed a PhD on the Northern Goshawk, worked as a conservationist and has studied
the Honey-buzzard for more than 20 years. Bernd-Ulrich Meyburg has carried out research on no fewer than
16 raptor species and marked several hundred birds of prey using satellite tags.
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481