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.