GYRFALCON FALCO RUSTICOLUS POST-GLACIAL COLONIZATIONAND EXTREME LONG-TERM USE OF NEST SITES IN GREENLANDKURT K. BURNHAM,1,2,†, WILLIAM A. BURNHAM,2,^, AND IAN NEWTON3
1

Edward Grey Institute, Department of Zoology, University of Oxford,
South Parks Road, Oxford, OX1 3PS, UK.
E-mail: kburnham@higharctic.org†

Present address: High Arctic Institute, 603 10th Avenue, Orion, IL 61273, USA
2

The Peregrine Fund, 5668 West Flying Hawk Lane, Boise, ID 83709, USA

3

Centre for Ecology & Hydrology, Maclean Building, Benson Lane, Crowmarsh, Gifford,
Wallingford, Oxon OX10 8BB, UK^

Deceased

ABSTRACT.—Gyrfalcons (Falco rusticolus) use the same nest-sites over long periods of time, andin the cold dry climate of Greenland, guano and other nest debris decay slowly. Nineteen guano
samples and three feathers were collected from 13 Gyrfalcon nests with stratified faecal accumulation in central-west and northwest Greenland. Samples were 14C dated, with the oldest guano
sample dating to c. 2740–2360 calendar years (cal yr) before present (BP) and three others werelikely > 1000 cal yr BP. Feather samples ranged from 670 to 60 cal yr BP. Although the estimatedage of material was correlated with sample depth, both sample depth and guano thickness gave amuch less reliable prediction of sample age than use of radiocarbon dating on which the marginof error was less. Older samples were obtained from sites farther from the current Greenland Ice
Sheet and at higher elevations, while younger samples were closer to the current ice sheet and atlower elevations. Values for δ13C showed that Gyrfalcons nesting further from the Greenland Ice
Sheet had a more marine diet while those nesting closer to the ice sheet (= further inland) fed ona more terrestrial diet. The duration of nest site use by Gyrfalcons is a probable indicator of boththe time at which colonization occurred and of the palaeoenvironmental conditions and patternsof glacial retreat. Nowhere before has such extreme long-term to present use of raptor nest sites
been documented. Reproduced with permission of the authors from Ibis (2009) 151:514–522.
BURNHAM, K. K., W. A. BURNHAM, AND I. NEWTON. 2011. Gyrfalcon Falco rusticolus post-glacialcolonization and extreme long-term use of nest sites in Greenland. Reproduced, pages 81–92 in
R. T. Watson, T. J. Cade, M. Fuller, G. Hunt, and E. Potapov (Eds.). Gyrfalcons and Ptarmigan ina Changing World, Volume II. The Peregrine Fund, Boise, Idaho, USA. http://dx.doi.org/
10.4080/gpcw.2011.0123
Key words: Carbon dating, guano, palaeoenvironmental conditions, δ13C.

81

– BURNHAM ET AL. –IT IS WELL KNOWN that raptors may re-use nest
sites for generations and some possibly forcenturies (Newton 1979). Hickey (1942)
referred to these nest sites as “ecological magnets.” These locations are evidently so desirable that they are re-used again and again, even
if the birds have no former familiarity with thelocation. For example, Peregrine Falcons(Falco peregrinus) disappeared from large
areas of North America and Europe during the
1960s as a result of organochlorine pesticideuse. Many years later, following the restrictionin the use of these chemicals, released or recolonizing Peregrines usually reoccupied former
territories first, frequently re-using the samenest ledges as their predecessors (Newton
1979, Ratcliffe 1993, Oakleaf 2003).

Figure 1. Gyrfalcon nest site 123 being sampled

for radiocarbon dating in Kangerlussuaq,
central-west Greenland, with a 14C age of 1160 to920 cal yr BP.

Gyrfalcons (Falco rusticolus) and Peregrine
Falcons both breed in the Arctic. Falcons do
not build nests, but lay eggs in bowl-shaped
depressions they scrape into existing substrates, including old nests made by otherbirds. Arctic Peregrine Falcons typically use
open ledges on cliffs for nesting with little protection from the weather (Cade 1960). Gyrfalcons usually nest on cliff ledges overhung by
rock, in potholes, or in sheltered stick-nests
built by Northern Ravens Corvus corax (Cade1960, Burnham and Mattox 1984). These
nesting situations provide protection fromfalling rock and the extreme weather conditions often found during the early part of the
Gyrfalcon breeding season. While stick nests
are frequently damaged beyond re-use in a single season, some ledges and potholes are used
long-term by Gyrfalcons (Burnham and Mattox 1984). Gyrfalcons and Northern Ravens
do not seem to alternate the use of the samenest site from year to year in Greenland. At reused sites, faecal accumulation frequently
occurs where Gyrfalcons roost and nest.
Deposited over periods of years, the stratified
accumulation of guano can become greaterthan 1.5 m thick in locations protected from
erosion and where dry and cold environmental
conditions enhance preservation (Figure 1).

There are many such nest sites throughout icefree areas of Greenland.
The Greenland Ice Sheet covers 82% of theland mass of Greenland (Ohmura et al. 1999),
and ice-free land occurs only along the periphery of the island. Nest-site availability for falcons may be affected by climate-induced
glacial retreat and advance covering andexposing cliffs. Long-term use of nest-sites by
Gyrfalcons is a potential indicator forpalaeoenvironments and of stable glacial conditions. As the ice sheet retreated, areas at
higher elevations, having a thinner layer of ice
and snow, were exposed first. Land at lower
elevations, particularly valley bottoms, had thethickest covering of ice and were exposed last(Fristrup 1966). We therefore hypothesizedthat guano in Gyrfalcon nests at lower elevations and closer to the current ice sheet would
have accumulated over shorter periods thanthat at nests at higher elevations and further
from the current Greenland Ice Sheet. To
investigate this question we sampled andradiocarbon dated guano from Gyrfalcon nestsites in two areas, in Kangerlussuaq, centralwest (66.50–67.00° N), and Thule, northwest(76.25–77.17° N), Greenland. These study
areas were separated by about 9° latitude and1100 km.

82

– GYRFALCON LONG-TERM NEST USE –STUDY AREAS

METHODSThe Kangerlussuaq study area is located at thehead of a 175-km-long fjord and about 25 kmfrom the current ice sheet margin. The Low
Arctic tundra landscape in this area wassculpted by glaciation, with rolling hills andvalleys, moraines and lakes, dissected by several meltwater rivers, and dominated mainly
by shrubs up to 2 m in height. Primary preyspecies for Gyrfalcons in Kangerlussuaq
include both Rock Ptarmigan (Lagopus mutus)
and Arctic Hare (Lepus arcticus), with lesser
quantities of passerines and waterfowl consumed (Booms and Fuller 2003). It is one of
the largest deglaciated land areas in Greenlandand, because of extensive past research, provides one of the most complete records ofGreenland’s glacial history (Ten Brink andWeidick 1974, Eisner et al. 1995). From projected rates of deglaciation (see below), we canestimate that some Gyrfalcon nest-sites may
have been uncovered c. 6500–6000 years
before present (yr BP).

Gyrfalcon nest-sites are distributed widely andirregularly throughout the two study areas andGreenland as a whole. All sites are on cliffs
and usually inaccessible without technical rockclimbing equipment. The amount of faecal
material build-up at sites varies greatly, as does
the structure and size of the nest. The rocksubstrate upon which falcon guano accumulates is usually irregular, sloping, and seldom
flat. Particularly on large ledges, the actual
nest scrape is not always in the same locationeach year, nor is the associated faecal deposition resulting from breeding. Also, the rates of
erosion are probably not constant across thenest, as some locations in the nest are more
protected from weather than are others. Therefore, the guano is not of constant depth
throughout the site, and it is difficult to know
where the thickest and/or oldest deposits maylie. At nest-sites where deposits seemed of
more-or-less uniform thickness throughout, asingle sample was collected where guano camein contact with the rock, while at other sites
more than one sample was collected in an
attempt to obtain the oldest guano. Bulk sample materials were collected from several centimeters of stratified guano, probably
representing accumulation over decades or
longer. Notes were made of sample depth(cm), cliff height (m), and nest ledge elevation(meters above sea level, m asl). All nests sampled had been occupied by Gyrfalcons within
the past 25 years (Table 1).

The Thule study area is centered around
Pituffik/Thule Air Base and the current ice
sheet margin lies up to 26 km inland from thesea, but it reaches the sea at several locations.
The environment is High Arctic with an
appearance of recent deglaciation, and sparsely
vegetated prostrate growing herbs and shrubs.
In this area, Gyrfalcons fed primarily on Little
Auks (Alle alle), Rock Ptarmigan and Arctic
Hares, with seabirds, waterfowl, and passerines taken in smaller numbers (Burnham
2008). Information on glaciation in Thule ismore limited than for Kangerlussuaq, and glacial history is predicted more from inference of
past climates than from moraine locations andmeasurement (Davies et al. 1963, Fredskild
1985, Kelly et al. 1999). Deglaciation sufficient to allow for consistent use of existingGyrfalcon nest sites may not have occurred
until 1350 yr BP or more recently (see below).

When collecting samples, layers of faecal
build-up were excavated carefully to prevent
damage of the site for future use by Gyrfalcons. At nest-sites with only a few centimetersof faecal build-up, we dug vertically down into
the guano, extracted samples at its base, andthen refilled the hole to minimize damage tothe nest site. At sites with substantial build-up,
samples were taken from the side by using a83

– BURNHAM ET AL. –Table 1. Results of the 14C measurements on guano material and feathers from Gyrfalcon nest sites in

Kangerlussuaq, central-west, and Thule, northwest Greenland, collected from 2002 to 2004. Samples
from the same nest site are designated by the use of A, B, C, or D following the number.

Nestsite

Beta Sample
analytic depth
sample # (cm)Distance
Cliff
Nest from ice δ13C
height elevation margin(‰)(m)(m asl)
(km)
(PDB)

Last
used

Conventional14
C age(yr BP ± 1σ)

Calibrated
age range(cal yr BP ± 2σ)

Kangerlussuaq, central-west Greenland019
195586 20–25
15
355

9

-22.7

1992

790 ± 60

790–650053A

191125

30–35

15

304

11

-22.4

1991

1290 ± 50

1300–1080

053B

191126

15–20

15

304

11

-22.4

1991

1090 ± 80

1180–900, 850–810

053Ca

191295

15

15

304

11

-22.5

1991

320 ± 30

470–300

068A

191127

15–20

152

55

14

-22.9

2000

570 ± 50

650–520068B

195576

10–15

152

55

14

-20.7

2000

240 ± 60

450–260, 220–140,
30–0

082

195577

25–30

76

441

5

-23.2

1999

830 ± 70

920–660

087A

168839

30–35

46

365

54

-21.9

2002

2480 ± 40

2740–2360

087B

168840

25–30

46

365

54

-20.9

2002

350 ± 40

500–300

087C

168838

0–3

46

365

54

-24.2

2002

105.09 ± 0.66 pMCb

outsidecalibration rangeb

087Da

168837

15

46

365

54

-21.3

2002

170 ± 40

300–60, 40–0

123195578

20–25

46

258

62

-21.1

~1985

1090 ± 60

1160–920

163

195587100-110

152

395

72

-20.8

2003

960 ± 60

970–740170

195579

15–20

24

103

28

-21.3

2004

690 ± 60

710–550

201A

195580

35–40

23

200

78

-17.8

2000

1430 ± 70

1480–1470,
1430–1250

201B

195581

10–15

23

200

78

-21.3

2000

820 ± 60

910–660

outsidecalibration rangeb
outsidecalibration rangeb
outsidecalibration rangeb

Thule, northwest Greenland
500A

195583

5–8

46

152

14

-23.3

2003

113.34 ± 0.71 pMCb

500B

195582

3–6

46

152

14

-21.2

2003

122.08 ± 0.73 pMCb

501

195584

2–4

117

122

2

-23.2

2004

115.29 ± 0.66 pMCb

502

195585

15–20

23

152

9

-20.2

2004

640 ± 50

670–540

503A

191124

20–25

76

304

17

-19.1

2004

650 ± 70

690–530

503Ba

191348

20

76

304

17

-19.5

2004

650 ± 40

670–550aGyrfalcon feather samples.

bpMC (percent Modern Carbon) analyzed material was post-1950 and had more 14C than did the AD 1950 reference
standard due to atomic bomb testing and subsequent fall-out, 50 years used as conventional 14C age while
Calibrated Age Range is outside calibration range.

84

– GYRFALCON LONG-TERM NEST USE –masonry hammer and a small trowel to excavate horizontally until rock was reached. The
amount of bulk material collected from thestratified samples varied, but in all cases was
sufficient for dating using standardized radiocarbon procedures. Within the nest sites,feathers (from probable prey and/or Gyrfalcons) and bones (prey) were found during
excavation. Three feathers that were easily
identifiable as from Gyrfalcons were alsoradiocarbon dated.

guano samples and two feathers were fromnine nests in Kangerlussuaq. To test for relationships between age of guano samples andnest variables (using JMP IN, vs. 4, SAS Institute Inc.), we analyzed the distribution of thevariables and relationships using Spearman
Correlation Analysis, as was most appropriate
based on the non-normal distribution of thedata. Conventional 14C age was used as the
maximum age for each sample.

Radiocarbon dating was carried out by Beta
Analytic Inc, Miami, Florida, USA, using
either the conventional radiometric technique(samples > 30 g) or accelerator mass spectrometry (AMS) (samples < 30 g). Guano samples
were pre-treated using an “acid wash”, whilean “acid/alkali/acid” wash was used for feather
samples. For the conventional radiometrictechnique, materials were analyzed by synthesizing carbon to benzene (92% C) and thenmeasuring for 14C in a scintillation spectrometer from which the radiocarbon age was calculated (Beta Analytic). AMS results wereobtained by the reduction of sample carbon tographite (100% C) along with standards andbackgrounds (Beta Analytic). Graphite wasthen sent for 14C measurement in an accelerator-mass-spectrometer to a research facility
collaborating with Beta Analytic. The measured radiocarbon ages were returned to Beta
Analytic where verification, isotopic fractionation correction using δ13C, and calendar calibration took place (Beta Analytic). Calibrated
results provide both a maximum and minimum
age for each sample in calendar years (cal yr)
before present (BP), with a 95% confidence
that the actual age falls within this range. Calibrations were made using calibration data
published in Stuiver et al. (1998) using cubic
spline fit mathematics, as described by Talma
and Vogel (1993).

RESULTSThe oldest guano sample was from nest site
087 in Kangerlussuaq and was dated 2740 to
2360 cal yr BP (Table 1). Three nests in
Kangerlussuaq showed evidence of occupation> 1000 cal yr BP, with the most recent nest
being occupied from 650 to 520 cal yr BP. In
Thule, the oldest nest was between 690 and
530 cal yr BP with two nests indicating use
only within the past 50 years (Table 1). Sites
in Kangerlussuaq have been used approximately 1800 to 2000 years longer than thosefurther north in Thule. Sites with multiple
samples collected showed an increase in 14C
age with sample depth (Table 1). The three
analyzed Gyrfalcon feathers were between 670
and 60 cal yr BP. Sample 087D had two possible calibrated age ranges, 300–60 and 40–0
cal yr BP, and the older range was most likely
accurate based on other samples from the samenest and sample depth. While the bulk samples of guano represent a number of years ofsite use, the feathers were from a precise
moment in time.
The maximum conventional 14C age for eachindividual nest was significantly correlatedwith the current distance from the ice margin(rs = 0.56, P < 0.05, n = 13, Figure 2), nest elevation (rs = 0.61, P < 0.05, n = 13, Figure 3),
and sample depth (rs = 0.88, P < 0.0001, n =13, Figure 4). While sample depth could be
used as a predictor of 14C age, the margin oferror would be much greater than if using radio
carbon dating directly (e.g., 087A and 163,
Figure 4)

From 2002 to 2004, 19 bulk guano samples
and three feathers were collected from 13 Gyrfalcon nest sites. Five guano samples and one
feather were from four nests in Thule, and 14

85

– BURNHAM ET AL. –distance from ice margin (km)In general, organisms from marine food chainsor animals that feed on them have less negativeδ13C values, while more negative δ13C values
are typically associated with terrestrial ecosystems (Rounick and Winterbourn 1986, Angerbjörn et al. 1994). The δ13C values from theoldest guano sample from each nest varied
slightly from a median of –21.9‰ (n = 9, σ2 =2.7) for Kangerlussuaq to –21.5‰ (n = 4, σ2 =4.5) for Thule, with no statistical difference
between the two areas. A significant correlation exists between δ13C for the oldest guano
sample from each nest and their current distance to the Greenland Ice Sheet (rs = 0.63, P< 0.05, n = 13), with less negative values being
associated with nests further from the current
ice sheet (Figure 5).

90
80

201a
163

70

123

60

087a

50
40
30

170

20

504a

500a 068a

10
0
0

053a

019

503

082

502

500

1000

1500

2000

2500

3000

conventional c-14 age (yrs BP)

Figure 2. Relationship between maximum 14C
age and nest site distance from current ice
margin (rs = 0.56, P < 0.05, n = 13).

500
450

nest elevation (m)DISCUSSIONRadiocarbon dating of Gyrfalcon nest material
from Kangerlussuaq and Thule, Greenland,
indicate much longer occupancy times thancan be determined from historical records.
Sites from Kangerlussuaq were colonizedapproximately 1800–2000 years earlier thanthose further north in Thule, probably an effectof earlier deglaciation and a more stable andwarmer climate in the Kangerlussuaq area.
These are some of the longest used raptor nest
sites ever documented.

082

400

163
087a

019

350

053a

503a

300

123

250

201a

200
500a
501

150
100

502
170
068a

50
0
0

500

1000

1500

2000

2500

3000

conventional c-14 age (yr BP)
Figure 3. Relationship between maximum 14C

age and nest site elevation (m above sea level)(rs = 0.61, P < 0.05, n = 13).

Similar studies of this type have been carriedout on other Arctic and Antarctic species.
These have included Snow Petrels (Pagodroma nivea) (Hiller et al. 1988), Thick-billed
Murres (Uria lomvia) (Gaston and Donaldson
1995), and Adelie Penguins (Pygoscelis
adeliae) (Emslie et al. 2007), for which radiocarbon age has been calculated using solidified
stomach oil deposits, peat moss deposits, andbone and feather samples from molting sites,
respectively, and minimum dates for the establishment or colonization of bird colonies havebeen given (~34000 yr BP, 1500–3800 yr BP,
and > 44000 yr BP, respectively). In addition,archaeological studies have sometimes
revealed long-term use of raptor nest-sites.

sample depth (cm)

120
163

100
80
60
40

201a
082
503a
053a
019
068a
170 123
500a
502
501

20
0
0

500

1000

1500

087a

2000

2500

3000

conventional c-14 age (yr BP)
Figure 4. Relationship between maximum 14C

age and sample depth (rs = 0.88, P < 0.0001, n= 13).

86

201A 80

80

60

60

40

40

20

20

0

0

163
123
087A

170
Rock
Snowshoe
PtarmiganHare(-24.4)(-26.4)

500A

068A
082
501

-24

503
053A

-23

502

019

-22

-21
δ13C ‰-20

LittleAuk

Black
Guillemot

-19

-18

-17

distance from ice margin (km)– GYRFALCON LONG-TERM NEST USE –Figure 5. Relationship between δ13C and distance from current ice margin (rs = 0.63, P < 0.05, n =13). Frequent prey of Gyrfalcons shown with associated δ13C value. Snowshoe Hare (Lepus
americanus) δ13C value was substituted for Arctic Hare as no values were found in the literature for
Arctic Hare. δ13C values for Snowshoe Hare, Rock Ptarmigan, Little Auk, and Black Guillemot are from
Roth et al. 2007, Ricca et al. 2007, Hobson et al. 2002, and Hobson et al. 2002, respectively.

sampled resulted from long-term use by falcons, and in particular Gyrfalcons.

For example, remains of Peregrine Falcons,
probably adults and nestlings, were found during an archaeological investigation of prehistoric human occupation of a cave on Hunter
Island, Tasmania (Bowdler 1984). Bones were
found in layers 990 ± 90 to ca. 19000 yr BP
suggesting use by falcons during that time but
not more recently.

The feather samples could be easily identified
to Gyrfalcons. Although interesting because of
their condition and long-term preservation,
they did not contribute to knowledge on duration of nest site use or palaeoenvironment
beyond what could be inferred from guano
samples. They did, however, provide confirmation of dates of past use.

There can be little doubt about the identity of
the Gyrfalcon sites in Greenland. Only two
falcon species breed there (Salomonsen 1950)
and although Peregrines sometimes use former
Gyrfalcon nest sites, these species typicallyselect different nesting situations, as explained
above. Cliff-nesting seabirds breed in different
situations than do falcons. Gulls nest colonially and sites cannot be confused with falcon
nests. Except for Iceland Gulls (Larus glaucoides) and Glaucous Gulls (L. hyperboreus),
all other avian species breeding in the researchareas construct nests containing sticks, grass,and feathers, and/or breed on the ground.
Ravens are the only other cliff-nesting species
that nest in similar locations to Gyrfalcons, butthey construct stick-nests. There can be no
doubt that the accumulation of guano at sites

Some nest-sites provided much older radiocarbon dated samples than others. Newton (1979)
attributed the repeated occupancy of nest sites
to “the superiority of particular places over
local alternatives.” This superiority could
result from a nearby abundance of prey, asuperior hunting platform, a location in appropriate spatial relationship to other territorial
pairs, or a site offering good protection frommammalian predators or inclement weather(rain, snow, sun, and/or wind). Over time, thedesirability of sites may change due to alteredenvironmental conditions, including rock
structure. This likelihood may be particularly
true in areas of recent glacial activity and climate change.

87

– BURNHAM ET AL. –addition, it was probably not until the “climatic
optimum,” from 4400 to 3400 yr BP, that thenecessary vegetation was established to support the prey-base utilized by Gyrfalcons in
Kangerlussuaq.

The Greenland Ice Sheet gradually retreatedabout 175 km in the Kangerlussuaq area
because of world-wide climate warming since
the end of the last glaciation (~15000 yr BP),but with frequent re-expansions (Ten Brink
and Weidick 1974, Funder 1989, Figure 6). A
slow retreat of the ice sheet (1 km/100 yr)
occurred from c. 15000 to 10000 yr BP followed by an oscillatory but more rapid retreat(3 km/100 yr) of nearly 100 km from c. 9500
to 6500 yr BP (Ten Brink and Weidick 1974).
By 6000 yr BP the ice sheet had reached its
present position, although between 5- and 10km re-advances occurred from c. 4800 to 4000
and from 2500 to 2000 yr BP (Ten Brink andWeidick 1974, Figure 6). At that time the sea
level was nearly equal to the present day. Eisner et al. (1995) reported that Kangerlussuaq
experienced a “climatic optimum” from c.
4400 to 3400 yr BP and that a climatically stable period is believed to have encompassed theperiod from 2000 to 1200 yr BP (Figure 6).
Based on lichenometry, the period from c. 700
yr BP to the present was characterized byoscillatory advance and retreat of the inland ice
within about a 3-km-wide zone (Ten Brink andWeidick 1974).

Information from Thule is far less complete
and more contentious than that from Kangerlussuaq. In Thule, Malaurie et al. (1972) useddata from marine deposits of terraces to estimate that deglaciation began c. 8000 yr BP,
and Kelly et al. (1999) postulate that much of
the area has been ice-free for at least 9000
years (Figure 6). From the period extending
8000—3000 yr BP, the Thule area experienced
a climatic optimum, with significant surface
melting occurring (Reeh 1984, Figure 6).
Archaeological evidence indicates unfavorable, cool conditions from 2500 to 1900 yr BP
followed by three centuries with a warmer climate (McGhee 1972, Figure 6). During theperiod c. 1350—900 yr BP, a moist and likely
warm climate prevailed, with conditions cooling and vegetation changing to drier heath at
the end of this period (Fredskild 1973, Figure6). From c. 900 yr BP to the 20th century, considerable climatic variability existed, but evidence from ice cores and oxygen isotopic
records from Camp Century show that generally cooler conditions probably persisted in theThule area until c. 1900 AD (Johnsen et al.
1970). Meteorological records from Upernavik, Greenland (72° 50' N), show a 2°C
mean annual temperature increase through the
middle of the 20th Century (Dowdeswell1996).

In Kangerlussuaq, nest-sites 019, 053, 068,
082, and 170 were probably covered by ice
during re-advances of glaciers from the Greenland Ice Sheet between c. 4800 and 4000 andfrom 2500 to 2000 yr BP. All five nest-sites
are in glacial valleys or river valleys and fourof the five are on low cliffs. The fifth site(053) is near to the top edge of a deep valley.
Furthermore, 068 and 170 are on small cliffs
near low elevation rivers and even a 10 m risein sea level could have affected use of thesesites by Gyrfalcons. Nest sites 087, 123, 163,
and 201 are less than 50 km from the ice edge
and, based on the projected rate of ice-sheet
retreat, these nest sites were ice-free by 6500–
6000 yr BP. That does not preclude, however,the possibility of isolated snow banks and glaciers covering nest sites, particularly on small
cliffs and at lower elevations, during periods ofclimatic cooling and glacial expansion. In

In Thule, the existence of consistent long-term
nest-site availability is more recent than in
Kangerlussuaq. While some nest sites may
have been ice-free as early as c. 9000—6000
yr BP, they may have been later re-covered byre-advances of the ice sheet. Furthermore,
despite some nest-sites being ice-free forextended periods of time, suitable environmental conditions for Gyrfalcons probably did notexist until between 1350 and 900 yr BP orlater. Even now, because of cool mean sum-88

– GYRFALCON LONG-TERM NEST USE –Kangerlussuaq

0 yr BPoscillatory advance/retreat

δ13C values with much wider ranges (–16.6 to–24.7‰, –18.1 to –24.1‰, ~ –17 to –21‰,
respectively), mainly as a result of seasonal
shifts in foraging between marine and terrestrial areas (Morrison and Hobson 2004, Braune
et al. 2005).

Thulefirst Gyrfalcon nest

1stable climate
2

minor ice re-advancefirst Gyrfalcon nest

3

climatic optimum?
minor ice re-advance

4

5,000
ice sheet at current position

warming period
cooling period

In Kangerlussuaq, δ13C values for each of theoldest 14C dated nests ranged from –23.2 to –17.8‰. Nest 082 has the most negative δ13C
value and is closest to the current ice sheet (5km), and nest 201A has the least negative δ13C
value and is farthest from the ice sheet (78 km,
Figure 5). Of particular interest is nest 087A,
which is the oldest sampled nest in Kangerlussuaq by ~1000 years, and has the median δ13Cof the nine nests sampled in Kangerlussuaq.
While this nest is 54 km from the current ice
sheet, it is approximately 1 km from a large
fjord, allowing adult Gyrfalcons potential
access to both a marine and terrestrial diet.
The benefit of readily accessing such a large
variety of prey may have allowed for earlier
colonization of the nest-site. For Thule, nests
500A and 501 have very negative δ13C values,
with nest 500A almost 100 km from the nearest breeding seabird colonies and prey remains
consisting almost solely of Arctic Hare in
recent years, and nest 501 in a large wetlandarea, with prey remains primarily consisting ofRock Ptarmigan. The other two Thule nest
sites, 502 and 503A, are in areas with large
numbers of Little Auks and Black Guillemots.
For both study areas, multiple samples fromthe same nest site show changes of up to –3‰
in δ13C over time (e.g., site 087 in Kangerlussuaq, Table 1), which is likely the result ofchanges in prey composition over time.

Holocene climatic optimum

6
7

rapid ice retreat

89?

10,00011

slow ice retreat

Wolstenholme Fjord glaciation
12
13
14

Figure 6. Glacial and climate history for the past

15000 yr BP for the Kangerlussuaq and Thulestudy areas. For sources on dates used in the
figure please see text.

mer temperatures, localized large snow banks
and glaciers can develop in just a few years or
decades and preclude the use of affected nest
sites.
The significant correlation between δ13C values and distance to the current ice sheet islikely a reflection of diet, with Gyrfalcons
breeding nearer the coast feeding on a mixed
diet of marine and terrestrial prey items, andthose breeding more inland having an almost
completely terrestrial diet. Primary terrestrial
prey items, such as Rock Ptarmigan and Arctic
hare, have likely δ13C values in the rangeof –24 to –27‰ (Figure 5, Ricca et al. 2007,
Roth et al. 2007) while marine prey items,
such as Little Auk and Black Guillemots (Cepphus grylle), have δ13C values ranging
from –18 to –20‰ (Figure 5, Hobson et al.
2002). Other prey species taken in more limited quantities, such as shorebirds (e.g., Red
Knot [Calidris canutus] and Ruddy Turnstone[Arenaria interpres]) and waterfowl (e.g.,Long-tailed Duck [Clangula hyemalis]) haveOn the basis of palaeoenvironmental investigations by others, we hypothesized that Gyrfalcon nest sites of higher elevations, andfurther from the ice margin, would show
longer usage patterns than nest sites closer tothe ice edge, and at lower elevations. Bothpredictions were confirmed using 14C dating.
Carbon dating of stratified guano accumulation
at Gyrfalcon nest-sites could thus be used to89

– BURNHAM ET AL. –LITERATURE CITED

confirm and date when local environments
were suitable for breeding by this species andwhen colonization probably occurred. Furthermore, past use of sites indicates that favorable environmental conditions existed for preyspecies as well. Values from δ13C provide
insight into likely prey species that existed at
the time of colonization and possible changes
in prey species over time. While results fromthis study are specific to Kangerlussuaq andThule, it is somewhat likely that similar correlations exist in other regions of Greenland.
These results shed further light on local, andprobably regional, palaeoenvironmental conditions and glaciation in the Arctic.

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ACKNOWLEDGMENTSFirst and foremost we thank Andrew Gosler,
Jennifer Burnham, Jeff Johnson, Chris Perrins,
and David Houston for comments and suggestions. Additionally, Konrad Steffen, University of Colorado, USA, provided helpful
remarks on this manuscript and suggested citations related to glaciation and paleoenvironments in Greenland.
Edward Hanna,
University of Plymouth, United Kingdom, provided further citations related to glaciation andpaleoenvironments in Greenland. Thank you
to the Greenland Home Rule Government andDanish Polar Center for providing permits forthis research. Additionally, the support of
KISS, VECO, 109th Air National Guard, andthe United States Air Force were critical in
supporting field work. Brian and Ruth Mutch,
Jack Cafferty, Jack Stephens, Robin Abbott,
Earl Vaughn, Ed Stockard, and the residents ofboth Kangerlussuaq and Thule Air Basedeserve special thanks for their continued
friendship and assistance. Financial support
was provided by The Peregrine Fund, Ruth O.
Mutch, The Offield Family Foundation, Peter
Pfendler, Comer Science and Education Foundation, and The G. Unger Vetlesen Foundationand is greatly appreciated.

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