Journal of Animal Ecology 2014, 83, 5–6
doi: 10.1111/1365-2656.12164
IN FOCUS
Tracking animals to their death
Satellite tracking is a tool for not only recording the long-distance movements of a range of species, but also for revealing animal mortality. (a) An osprey equipped with a satellite tag to record its migration from Europe to Sub-Saharan Africa. Photo: Raymond Klaassen. (b) A dead osprey. Satellite tracking can identify when and where animals die and also sometimes the cause of death. Photo: Ewan Weston. (c) This technique can also be used with other taxa. A loggerhead turtle satellite-tracked to its death in Greece. Propeller marks indicated that this individual had been hit by a boat before washing ashore dead. Photo: Gail Schofield.
In Focus: Klaassen, R.H.G., Hake, M., Strandberg, R., Koks, B.J., Trierweiler, C., Exo, K.-M., Bairlein, F. & Alerstam, T. (2014) When and where does mortality occur in migratory birds? Direct evidence from long-term satellite tracking of two raptors. Journal of Animal Ecology, 83, 176–184. Migration may be a high-risk period. In a study involving three species of raptor migrating from Europe to Sub-Saharan Africa, Klaassen et al. (2014) satellite-tracked 51 out of 69 birds to their deaths and showed that rate of mortality during migration was 6x that during stationary phases when birds were on their winter and summer grounds. Travel across the Sahara was particularly risky. Satellite tracking has also been used to infer mortality in other taxa (e.g. sea turtles) and may allow high-risk hotspots to be identified for wide-ranging species.
‘In this world nothing can be said to be certain, except death and taxes’ Benjamin Franklin.
For ecologists, this quote will strike a chord. For some poorly paid ecologists, perhaps it might be the issue of taxes that resonates, but for most it will be the sentiment that death is all pervading in ecological studies. Death, or mortality as it is generally termed, is a fundamental component of many ecological studies: from demographic studies that describe population dynamics to studies that focus on drivers of individual fitness. As such is it no surprise that for many decades ecologists have devised methods to estimate mortality. One approach is to measure the number of individuals of different ages within a population, from which life tables and survivorship curves of the age-specific mortality rate can be derived. This approach produces an estimate of mortality for a population. But sometimes the goal is to record the fate of known individuals and hence assess the drivers of individual fitness. In this case, biotelemetry has long been Correspondence author. E-mail: [email protected]
used as a tool to help estimate mortality. With conventional radiotracking, animals can be located from a few km away using a directional antenna and receiver. Sometimes, other data (e.g. motion) may also be relayed. When the received data indicate that the tag has not moved for a long period, this often implies that the animal has died which may then be confirmed by relocating the tag (e.g. Brand, Vowles & Keith 1975; McLoughlin et al. 2003). In this issue, Klaassen et al. (2014) extend this approach by using satellite tags to estimate the mortality of three species of raptors migrating from Europe to Sub-Saharan Africa: ospreys (Pandion haliaetus), Marsh harriers (Circus aeruginosus) and Montagu’s harrier (Circus pygargus). These birds perform some of the longest animal migrations, with round trips of many 1000s of km, which rival the longest travel distances seen in birds and other taxa (Hays & Scott 2013). Birds were equipped with light (
doi: 10.1111/1365-2656.12164
IN FOCUS
Tracking animals to their death
Satellite tracking is a tool for not only recording the long-distance movements of a range of species, but also for revealing animal mortality. (a) An osprey equipped with a satellite tag to record its migration from Europe to Sub-Saharan Africa. Photo: Raymond Klaassen. (b) A dead osprey. Satellite tracking can identify when and where animals die and also sometimes the cause of death. Photo: Ewan Weston. (c) This technique can also be used with other taxa. A loggerhead turtle satellite-tracked to its death in Greece. Propeller marks indicated that this individual had been hit by a boat before washing ashore dead. Photo: Gail Schofield.
In Focus: Klaassen, R.H.G., Hake, M., Strandberg, R., Koks, B.J., Trierweiler, C., Exo, K.-M., Bairlein, F. & Alerstam, T. (2014) When and where does mortality occur in migratory birds? Direct evidence from long-term satellite tracking of two raptors. Journal of Animal Ecology, 83, 176–184. Migration may be a high-risk period. In a study involving three species of raptor migrating from Europe to Sub-Saharan Africa, Klaassen et al. (2014) satellite-tracked 51 out of 69 birds to their deaths and showed that rate of mortality during migration was 6x that during stationary phases when birds were on their winter and summer grounds. Travel across the Sahara was particularly risky. Satellite tracking has also been used to infer mortality in other taxa (e.g. sea turtles) and may allow high-risk hotspots to be identified for wide-ranging species.
‘In this world nothing can be said to be certain, except death and taxes’ Benjamin Franklin.
For ecologists, this quote will strike a chord. For some poorly paid ecologists, perhaps it might be the issue of taxes that resonates, but for most it will be the sentiment that death is all pervading in ecological studies. Death, or mortality as it is generally termed, is a fundamental component of many ecological studies: from demographic studies that describe population dynamics to studies that focus on drivers of individual fitness. As such is it no surprise that for many decades ecologists have devised methods to estimate mortality. One approach is to measure the number of individuals of different ages within a population, from which life tables and survivorship curves of the age-specific mortality rate can be derived. This approach produces an estimate of mortality for a population. But sometimes the goal is to record the fate of known individuals and hence assess the drivers of individual fitness. In this case, biotelemetry has long been Correspondence author. E-mail: [email protected]
used as a tool to help estimate mortality. With conventional radiotracking, animals can be located from a few km away using a directional antenna and receiver. Sometimes, other data (e.g. motion) may also be relayed. When the received data indicate that the tag has not moved for a long period, this often implies that the animal has died which may then be confirmed by relocating the tag (e.g. Brand, Vowles & Keith 1975; McLoughlin et al. 2003). In this issue, Klaassen et al. (2014) extend this approach by using satellite tags to estimate the mortality of three species of raptors migrating from Europe to Sub-Saharan Africa: ospreys (Pandion haliaetus), Marsh harriers (Circus aeruginosus) and Montagu’s harrier (Circus pygargus). These birds perform some of the longest animal migrations, with round trips of many 1000s of km, which rival the longest travel distances seen in birds and other taxa (Hays & Scott 2013). Birds were equipped with light (
