INTRODUCTION
The global loss of biodiversity is well-documented, with increasing
numbers of species at risk of extinction due to direct or indirect
anthropogenic causes (Mora et al., 2013; Seddon et al., 2014).
Management to reduce the risk of species’ extinction includes a wide
variety of actions, including reintroduction. Reintroductions are
intentional translocations of species into parts of their historically
known range from which they have been extirpated (IUCN, 2013). Wildlife
reintroductions are becoming increasingly common, being now considered
an important tool for the conservation of endangered or threatened
species (Armstrong and Seddon, 2008; Soorae, 2016).
Birds of prey (raptors and vultures) are frequently involved in
reintroduction programs. Several such programs have been successful and
typically involve a common practical method: ‘hacking’ (Evans et al.,
2009; Ferrer et al., 2018). This method involves taking large nestlings
(typically when around two-thirds toward fledging in growth) from a
robust donor population and transferring them to the incipient novel
population via hacking facilities. Usually, donor nestlings are
translocated to artificial nest(s) inside hacking facilities
(effectively large aviaries) situated geographically in the recipient
area for the new population. During this period translocated birds are
fed ad libitum until they are released from aviaries once it is
judged that the birds are capable of free flight (effectively simulating
‘natural’ fledging age: Muriel et al., 2011).
Reintroductions by means of the hacking method appear especially
effective in birds of prey (Cade, 2000; Evans et al., 2009; Ferrer and
Morandini 2017, Morandini and Ferrer 2017a) and therefore can be used as
potentially useful tools for population restoration with appropriate
planning, development and monitoring (IUCN, 2013; Morandini and Ferrer,
2017b). There is evidence that in some species at least, manipulation
associated with hacking (extraction of the nestlings, ringing and
tagging them, unlimited amounts of food, keeping them in captivity for
some period, absence of parents) seems to have non-harmful effects on
survival, subsequent reproduction, habitat selection or dispersive
behavior (Morandini and Ferrer, 2017a; Ferrer and Morandini 2017;
Morandini et al., 2017, 2019; Muriel et al., 2015, 2016, 2020).
Nevertheless, as far as we know there are no studies on potential
consequences of health and nutritional condition due to the hacking
method, where food is provided ad libitum and there is no contact
with the parents after translocation.
Avian blood chemistry and blood cell analyses can detect possible
pathological states (Meredith et al., 2012). An adequate knowledge of
hematological values is recommended for projects involving research and
management of populations since they can be valuable for the assessment
of the nutritional levels and health status of constituent individuals
(Ferrer and Dobado-Berrios, 1998; Meredith et al., 2012; Ferrer et al.,
2017a, b). Despite the technology to analyze concentrations of blood
constituents being widely available and well understood, studies of
blood parameters in free-living raptors are still few (Viñuela et al.,
1991; Dobado-Berrios and Ferrer, 1997; Ferrer and Dobado-Berrios, 1998;
Meredith et al., 2012; Hernandez and Margalida, 2010; Montolio et al.,
2018; Flo et al., 2019). Hematological values, including chemical
components, are known to be influenced by many factors: physiological
state, age, sex, nutritional condition, circadian rhythm, seasonal
changes, captivity, pollutants, and plasma storing methods (Gee et al.,
1981; Rehder and Bird, 1983; Ferrer et al., 1987; Garcia-Rodriguez
et al., 1987a, b; Viñuela et al., 1991; Jenni-Eiermann and Jenni, 1992).
Translocations and reintroductions seem likely to be used more
extensively in the future, especially in the face of rapid global
changes and corresponding distributional shifts of certain species, but
also with regard to the favorable socio-ecological conditions that
remain within the former ranges of threatened species. Consequently, it
is important to improve our understanding of the limitations and
applications of associated techniques, sharing results and thus
increasing our expertise in wildlife restoration strategies.
The aim of this study was to analyze the potential effect of hacking on
health and nutritional status of White-tailed Eagle (WTE:Haliaaetus albicilla ) nestlings, in over 50 birds translocated
from western Norway to eastern Scotland. Blood samples were taken at two
events and subsequently analyzed using hematological and biochemical
metrics. The first sample was obtained when birds had been transferred
to Scotland soon after translocation, and the second after birds had
been held in captivity and fed ad libitum for c. 44 d shortly
before their release from captivity. We used this double sampling
(including biometric data) across the hacking period, to examine if the
period of captivity had caused any deterioration in health or
nutritional status. Alternatively, the hacking method may have been
beneficial with ad libitum food improving the health and
nutritional status of translocated birds during captivity.