Study species and area
WTE is a large bird of prey with females being larger than males. The
species is Eurasian in distribution and ecologically the Old World
equivalent of the New World’s Bald Eagle (Haliaeetus
leucocephalus ). Our study was involved with the second phase (east
Scotland) of a reintroduction initiative instigated by an initial (1975
– 1985: 82 birds) reintroduction and later reinforcement translocations
(1993 – 1995: 59 birds) using birds from western Norway to the west
coast of Scotland (Green et al., 1996; Evans et al., 2009; Whitfield et
al., 2009a, b; Sansom et al., 2016). The core initiative allowing our
study aimed to provide a further nucleus of WTE population growth on the
east coast of Scotland, situated away from the previous centers of
population re-establishment and subsequent expansions on the west coast.
We sampled nestlings extracted from a wild donor WTE population in
Norway: every June between 2007 and 2012 WTE nestlings were collected
from monitored nests in the western counties of Møre og Romsdal,
Hordaland and Sogn og Fjordane. Single birds were extracted from nests
that had two or three chicks which from field observations were deemed
old enough (five to eight weeks old) to be suitable for translocation on
plumage features and physical appearance (Helander, 1981). Extractions
were coordinated with the goal of a balanced sex ratio (based on
biometrics). Birds were uniquely metal banded (BTO: British Trust for
Ornithology) in Norway prior to translocation, for subsequent
identification.
There were extractions of 15 (2007, 2008, 2009), 19 (2010), 16 (2011)
and six (2012) nestlings per annum, resulting in 86 translocated birds
(85 were released as one 2009 bird died in captivity from aspergillosis,
despite veterinary intervention). Of these, 55 were double sampled for
biochemical and hematological parameters 2009 – 2012 and are the
subject of this study.
After transport from Norway, all birds had a full clinical examination
within 24 h of arrival to identify any potential abnormalities.
Translocated birds were kept at a hacking facility in northeast Fife,
southeast Scotland, in wooden (three sides enclosed) and wire mesh
aviaries measuring approximately 3.6 x 3 x 2.7 m that had ‘nesting’
platforms covered in bark chips and soft vegetation, and at least two
long perches. Two or three birds were housed in each aviary, with
similarly sized birds being kept together. Birds were supplied withad libitum food involving the wide range exploited by WTE (e.g.
Whitfield et al., 2013): fish, birds and mammals, with vitamin and
mineral supplements (Nutrobal®, Vertak, UK) added to the food daily.
Contact with humans was minimized by food being provided via a hatch in
the aviaries’ back panel. Captive eagles were kept under daily
observation via ‘spy holes’ in aviaries’ back panels for surveillance of
their status and any signs of injury or ill-health, with a qualified
veterinarian on call should the need arise: no eagles were injured
because of our activities.
The first sampling was undertaken shortly after all birds were in the
hacking facility. This allowed for greater efficiency in sampling all
birds at the same time after extraction and transportation from Norway
to Scotland (Table 1). The second sampling was taken shortly before
birds’ release from captivity when they were also fitted with patagial
wing tags or color-bands and a VHF telemetry tag, when biometric data
(including body mass) were again taken (Table 1). Birds were aged (days
since hatch date) using the method of Løseth et al. (2019): after T.
Nygård pers. comm.) involving measurement of a central tail feather.
This method was preferred to those in Helander (1981) and Helander et
al. (2007) involving other recorded biometrics when like Løseth et al.
(2019) we also found the “Nygård” method to produce more realistic and
consistent results.