Home-range size and habitat use of European Nightjars Caprimulgus europaeus nesting in a complex plantation-forest landscape
Nightjar populations have increased in recent years, but some declines have been noted at sites supporting nationally important breeding populations. BTO research is using tracking technology to better understand the habitat requirements of this cryptic yet charismatic species, so that habitat can be optimally managed to conserve them.
Although the British Nightjar population is generally faring well, increasing by 36% between 1992 and 2004 (Conway et al. 2007), there have been declines at some sites supporting regionally and nationally important numbers of this species. These declines have been attributed to the lack of available breeding habitat, but other factors may also be important, including disturbance through recreational activities and suboptimal habitat management.
During the breeding season, nesting habitat typically includes heathland and young conifer plantation. As both these habitats are dynamic, they require appropriate management to either maintain suitability for Nightjars, or to create replacement habitat when formerly suitable areas become overgrown. This can be achieved through felling and replanting in forest systems. However, foraging habitat is also essential for Nightjars and relatively little is known about which habitat types are the most important. It is also crucial to understand how close foraging and breeding habitats have to be for Nightjar management to be effective. Ultimately, land managers need appropriate habitat management guidance to ensure that the number of Nightjars that can be supported on a particular site is maximised, particularly where numbers have decreased.
Use of technology
It is difficult to observe nocturnal Nightjar activity, especially as birds may rapidly move substantial distances. A newly-published BTO study used VHF radio tracking devices to overcome this, following 31 individuals in Thetford Forest, East Anglia during 2009 and 2010 (Sharps et al. 2015). The results showed that conifer plantations aged 5-10 years were an important component of all territories, while newly planted forest (0-4 years) and grazed grassland were also used by Nightjars; all potentially important for foraging. Nightjars travelled a mean maximum distance of 747 m between breeding and feeding locations each night, demonstrating the importance of having foraging and nesting habitats in close proximity.
Following rapid advances in technology, GPS devices are now available, which can collect substantial quantities of high precision data. In 2014, 15 breeding Nightjars were successfully tracked with GPS in Thetford Forest and at Dersingham Bog National Nature Reserve, providing an objective and highly detailed insight into their movements. Initial analyses indicate that rapid foraging flights, often exceeding 3 km, are undertaken at dusk and dawn, to reach discrete locations that are re-visited on subsequent nights. During 2015, these apparent foraging hot spots will be further investigated with visits to observe actual Nightjar activity and examine prey abundance. Understanding the importance of these primary feeding locations and how they are used, will provide further improvements to landscape management operations and great benefits to Nightjar conservation.
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