Animal Movement - Mobility Data - page 275

to the fact that only animals surviving the movement can usually be recovered.
Despite such limitations, simple methods have allowed researchers to learn
important information about the life history traits of many species. 1
In general, the use of telemetry has improved the sampling design, reduced
bias, and improved reliability. In this paper, we denote by biologger any animal-
borne device able to record position and/or environmental/physiological data.
Miniaturization of GPS devices has allowed development of small and light
devices that can be fitted to a large number of animal species. It was possible
to shift by a collection of spatio-temporal positions (more or less statistically
independent) as done using VHF telemetry to a very dense (and highly corre-
lated) sampling of locations, which may represent an approximation of the actual
path followed by the animal. GPS devices use different technologies to transmit
position data. The GPS store-on-board (SOB) devices are recovered after use
and data are downloaded. SOBs are usually cheap but require that one is able to
recapture the animal or recover the device; SOBs can be used for nesting birds or
other animals likely to be easily recaptured or harvested. Drop-off mechanisms
that should cause the detachment of the SOB from the animal do not always per-
form well. GPS-GSM use a GSM (Global Service for Mobile Communication)
public network to exchange data between the biologger and the user, often using
small message services (SMS). Cleary this method is useful only in those coun-
tries where there are dense GSM networks. In other situations there are several
systems to remotely download GPS collars and retrieve the data. Probably the
cheapest method is to use a VHF beacon. The receiver can approach the tagged
animal on the terrain or using an airplane. This system is useful in wild areas
where the amount of data to recover is limited. The alternative is transmitting
data to a satellite constellation. There are several possibilities: to exploit the
Argos DCLS transmission, which allows only one-way transmission from the
animal to the user, or using satellite mobile phone systems (namely Iridium and
Globalstar services).
13.2.2 Interpretation of Animal Movement
As happens in human mobility (see Chapter 1 ), wildlife telemetry has quickly
changed in the last years; “a brave new world” (Tomkiewicz et al., 2010) arose
and now researchers have an array of technologies able to record the trajecto-
ries of many species of wild animals with high accuracy and in many different
ecological conditions, from the desert to the deep ocean, worldwide. It is funda-
mental to be able to exploit efficiently the information contained (some might
say “hidden”) in movement data for a large array of scientific and management
purposes. An important consequence of the use of biologging in ecology is the
1 See, e.g., http://www.phidot.org/software/mark/docs/book/