Valentine, one of the BTO-tagged Cuckoos, by Neil Calbrade / BTO
PUBLICATIONS | Tracking studies
Fitting devices, such as this satellite tag, provides information that furthers our understanding of many aspects of bird biology, including migration, foraging, diving and flight behaviour, habitat use, energetics, survival and dispersal.
Tracking tag effects BTO’s work on Cuckoos and other Afro-Palaearctic migrants provides an excellent example of the ways in which tracking devices have revolutionised our knowledge of bird migration. Such devices have now been used for more than 50 years and have greatly improved our understanding in many areas of ecology. In this article, Stephen Baillie, Graham Geen and Rob Robinson examine what effects they have on the birds that carry them. We undertook a near comprehensive review
REFERENCES Brlík, V, Koleček, J, Burgess, M, et al. (2019). Weak effects of geolocators on small birds: a metaanalysis controlled for phylogeny and publication bias. Journal of Animal Ecology 89: 207–220. Geen, G.R., Robinson, R.A., Baillie, S.R. (2019). Effects of tracking devices on individual birds – a review of the evidence. Journal of Avian Biology, doi.org/10.1111/jav.01823
28 – LIFECYCLE
of studies published between 1968, when the first radio-tracking studies started to appear, and the end of 2017. Our aim was not just to document the growth and range of tracking studies, but also to assess the effects that tracking devices may have on individual birds. For obvious ethical reasons, but also to provide robust scientific results, it is essential that any effects of such devices are minimised, and that the presence of effects should be properly monitored. In total we looked at 3,453 papers, a feat that took over four years to complete! It comes as no surprise that the number of tracking studies has increased exponentially, from only one or two publications per year in the 1960s, to around 300 papers per year today, an average increase of 4.4% per year. The earliest studies involved simple radio transmitters, followed by the introduction of data loggers in the 1970s and satellite tags in the late 1980s. Technologies have expanded further since the turn of the century, with the widespread application of geolocators and devices that link to the GPS or GSM (mobile phone) networks.
The priority given to different ecological questions, and the technologies needed to address them, varies between bird groups. For waterbirds, the main study topics have been migration, habitat use and survival, while for seabirds there is a huge emphasis on understanding their foraging behaviour at sea, reflecting the need for this information in relation to the planning of marine developments such as wind farms. For land birds, migration and habitat use have been the most frequent study topics, followed by survival. Over the last 15 years, developing technologies have revealed the migration routes of long-distance migrants in ever-increasing detail and this trend continues. Of the papers we examined, 1,560 provided information on whether or not effects were observed and out of these studies 38% actually recorded effects. It is important to emphasise here that we looked at all types of effects, ranging from increases in preening behaviour in the hours following the fitting of harnesses all the way through to (fortunately rare) direct observations of mortality, or reduced return rates of marked birds. The scope of Winter 2020
