APPLICATION OF TRACKING AND DATA-LOGGING TECHNOLOGY IN RESEARCH AND CONSERVATION OF SEABIRDS

Seabirds are the most conspicuous and mobile of all pelagic marine organisms. Because most species breed colonially, researchers can study statistically large samples with relative ease. These attributes have long made seabirds valuable for interpreting conditions in the surrounding oceans (Furness and Camphuysen 1997, Boyd et al. 2006, Piatt et al. 2007). Until recently, such studies were usually based on data obtained at breeding colonies or from vessels, but in the past two decades, advances in electronic technology have greatly changed the way we study seabirds, providing unprecedented insights into their locomotion, physiology, foraging behavior, migration, demographics, and exposure to anthropogenic risks at sea. In oceans that are rapidly changing as a result of human activities and global climate change, this information from tagged birds is timely and essential for developing conservation and management strategies for such wide-ranging organisms. In addition, seabirds are increasingly being viewed as tools for oceanography and climatology—capable of providing essential physical and biological information on the sea itself. "… advances in electronic technology have greatly changed the way we study seabirds, providing unprecedented insights into their locomotion, physiology, foraging behavior, migration, demographics, and exposure to anthropogenic risks at sea." Here, we highlight some of the exciting new techniques and data that are emerging, discuss some current and future applications, illustrate the roles that seabirds might play in monitoring this watery planet, and discuss the application of new technology in the conservation and management of seabirds. We focus here on La Grangian approaches, concerned with a sequence of data values at points occupied by an individual organism (Schneider 1994), in contrast to studies of populations or communities made at colonies or from vessels or aircraft. The burgeoning market for consumer electronics and communication (e.g., satellite and cell-phone communication) is partly responsible for the advances and miniaturization of sensors, memory storage, and batteries that are revolutionizing marine ornithology (see reviews in Wilson et al. 2002a, Ropert-Coudert and Wilson 2005). We review some recent developments, focusing on devices that tell us where birds go (satellite tracking, geolocators, global positioning system [GPS] loggers, and depth recorders) and what they are doing (sensors coupled with data loggers). Tracking devices.—Before 1990, conventional VHF radio tags were used to monitor colony attendance and near-colony foraging movements in seabirds (e.g., Anderson and Ricklefs 1987). This technology has severe limitations in location precision and range (typically 15–20 km from a high vantage point) but remains useful for studying at-sea behavior in small seabirds that cannot carry larger devices or that forage in nearshore waters (e.g., Irons 1998, Jodice and Collopy 1999). Since Jouventin and Weimerskirch's (1990) pioneering work, there has been a flood of studies using satellite telemetry (platform terminal transmitters [PTTs]) on seabirds (>100 papers published since 1990). Using the Argos satellite system, these studies revealed long-range movements of free-ranging individuals from all four major orders of seabirds. Platform terminal transmitters can provide up to 20 locations per day with accuracy typically 1–3 km. Units weighing as little as 9 g are in use, and some incorporate solar power to reduce battery size and enhance longevity. Given that location data are transmitted and not stored, tag recovery is not mandatory. Thus, it is the only reliable technique for evaluating the initial dispersion and habitat use of fledgling pelagic seabirds, where tag recovery is nearly impossible (Kooyman et al. 1996, Weimerskirch et al. 2006a). Global location sensing (GLS), or geolocation, uses changes in ambient light levels to estimate sunrise, sunset, day length, and, hence, longitude and latitude (Wilson et al. 1992). The spatial resolution is coarse (one or two locations per day; mean error 185–200 km; Phillips et al. 2004a, Shaffer et al. 2005). Adding temperature sensors to the GLS tag can improve location accuracy by using latitudinally stratified sea-surface temperatures to refine location estimates (1–2° error reduction; Teo et al. 2004, Shaffer et al. 2005). Despite its limitations compared with satellite telemetry, this technology has several advantages. Power consumption is minimal, because data are stored and not transmitted, which allows small batteries and tiny tags (e.g., 1.5-g units developed by the British Antarctic Survey). Slightly larger tags can record location data for 2–10 years. The primary application has been used to study the long-range movements of seabirds outside the breeding period (e.g., Weimerskirch and Wilson 2000; Croxall et al. 2005; Phillips et al. 2005, 2006; Shaffer et al. 2006; González-Solís et al. 2007), revealing remarkable movements across ocean basins (Fig. 1). A Sooty Shearwater (Puffinus griseus) tracked from Codfish Island, New Zealand, with an archival GLS tag that measured location, diving depth, and temperature. The bird made several excursions to Antarctic waters when breeding and then traveled to Alaska on migration. Note the lack of diving when crossing warm equatorial waters (A and B). Data are from (Shaffer et al. 2006). Another coarse and seldom-used tracking tag records each change in azimuth (or bearing) as a bird moves and "recreates" the track based on the summation of directional vectors and estimated flight speed (Benvenuti et al. 1998). Given that ground speeds vary with wind speed and flight direction, this method would likely perform better in flightless species like penguins (e.g., Wilson et al. 1991b) that have a more limited range of travel speeds (1–3 m s−1). However, a recent refinement of this technology is now incorporated in a new tag design called the "daily diary" (R. P. Wilson pers. comm.) that uses a three-axis accelerometer in addition to a directional compass. This new tag appears to overcome many of the previous challenges, and it monitors acceleration, body motion, and orientation in three dimensions. With GPS, locations can be recorded every second at accuracies within meters of true location, and GPS tags are now relatively inexpensive and small enough (~20 g) to be used on many seabirds (e.g., Weimerskirch et al. 2002a, Grémillet et al. 2004, Hamer et al. 2007, Phalan et al. 2007). The fine spatial resolution reveals unparalleled details of ground speed, micro-movements, and area-restricted searching behavior (Fig. 2). H. L. Young and S. A. Shaffer (unpubl. data) tracked Red-footed Boobies (Sula sula) with GPS data loggers (sampling every second) from Palmyra Atoll in October 2007. This particular bird was at sea for less than one day and traveled 146.7 km. Note the dramatic change in flight behavior at the maximum range from the colony. Maps A, B, and C show the movements at progressively finer resolution. The box in panel B is enlarged in panel C. Radar, theodolites, and thermal detection systems have been used in a wide range of applications for tracking movements, speeds, and numbers of flying seabirds (e.g., Pennycuick 1982, Alerstam et al. 1993, Day et al. 2004, Desholm et al. 2006), but these applications were not focused on logging data from individuals, which is the primary focus of our review. A digital surveying theodolite placed at a high vantage point (e.g., cliff or ship deck) allows fine-scale analysis of individual birds' locations and movements at scales of 1–5 m (Ronconi and Cassady St. Clair 2002). Multiple birds can be observed in rapid succession, and birds can be observed without the need to capture or alter their behavior, but the method is obviously limited to nearshore observations (<1 km from shore) during daylight. Data loggers to study behavior and physiology.—External attachment or implantation of miniaturized sensors linked to data loggers is now extremely widespread (reviews by Wilson et al. 2002a, Ropert-Coudert and Wilson 2005). Data loggers do not require long-distance signal reception, but, as with GPS and GLS recorders, an obvious limitation is that birds have to be recaptured or pass close to a remote data-recovery system to download the information, which generally restricts application to breeding birds. Time-depth recorders (TDRs) using pressure sensors to record diving depths and underwater foraging profiles were among the first data loggers (Kooyman et al. 1971) and continue to be extremely valuable (>100 publications on avian diving). Depth sensors have become increasingly sensitive, allowing fine-scaled changes associated with prey-capture to be identified (Ropert-Coudert and Wilson 2005). Time-depth recorders, coupled with accelerometers capable of recording very small movements (e.g., acceleration in pursuit of prey), show how, where, and when diving birds catch prey (Watanuki et al. 2003). Pressure sensors that determine altitude have revealed the flight patterns of soaring frigatebirds and explained their adaptations for exploiting sparse and widely dispersed food in tropical seas (Weimerskirch et al. 2003b). Loggers that record atmospheric pressure will also help to elucidate how wide-ranging seabirds avoid or exploit weather systems for long-distance travel (e.g., Murray et al. 2003, Catry et al. 2004a). Externally mounted temperature sensors (usually attached to leg bands) reveal activity patterns when volant seabirds are on or off the ocean (Weimerskirch et al. 1995) and yield important information about the water masses in which birds forage (Shaffer et al. 2006; Fig. 1B). Temperature sensors implanted within the body cavities or tissues of seabirds have provided valuable insights into the physiological performance and foraging tactics of free-ranging birds (e.g., Handrich et al. 1997). Similarly, sensors placed directly in the stomachs can reveal the time of prey intake, indicated by sharp drops in stomach temperature (e.g., Weimerskirch et al. 1994b, Catry et al. 2004b). Efforts to estimate the mass of food intake from declines in stomach temperature can be unreliable because they do not uniformly sample the ingested food and do not reliably detect the rapid ingestion of small items (Grémillet and Plös 1994, Wilson et al. 1995). Furthermore, significant changes in abdominal temperature, independent of food intake, have been recorded in penguins and cormorants (Wilson and Grémillet 1996, Bevan et al. 1997, Handrich et al. 1997). Implanted heartbeat sensors have shown the varied and subtle physiological adaptations for diving and oxygen consumption in birds (Kooyman 1989, Bevan et al. 1997, Butler 2004). Heartbeat sensors, usually backed up with the use of doubly labeled water, have also been used to monitor locomotion costs, foraging effort, and flight behavior (e.g., Bevan et al. 1995, 1997; Weimerskirch et al. 2000, 2001) and have revealed hitherto unsuspected stress in nesting birds caused by human activities (Wilson et al. 1991a, Weimerskirch et al. 2002b). Magnets are being applied in innovative ways to record fine movements of birds' appendages. Tiny magnets and magnetic sensors glued on either of (Wilson et al. Wilson or (Wilson et al. have provided records of and prey ingestion at the and and at the with tracking magnets glued to the have been used to the of in by seabirds (e.g., et al. 2003, et al. 2005). is allowing to be attached to larger seabirds by et al. 2007). et al. used to foraging behavior in and (Grémillet et al. used on cormorants to underwater foraging and With we that will become a major for studying birds. studies now sensors and several data (e.g., satellite tracking, doubly labeled to a more of what is at sea. studies have the use of satellite telemetry, activity loggers, and doubly labeled water or loggers to to foraging and in et al. 1995, Weimerskirch et al. 2000, Shaffer et al. Similarly, tracking loggers, and stomach temperature loggers have been to monitor foraging and flight activity (Weimerskirch et al. 1994b, Phalan et al. 2007). of prey by birds is obviously more when with information on the location and depth where the prey was satellite tracking with analysis of stomach et al. or et al. 2007). information on the location of foraging seabirds with ocean such as sea temperature, sea an of and greatly of habitat and of foraging (e.g., et al. Weimerskirch et al. Shaffer et al. 2006). of data loggers and satellite tracking to determine the location of birds and analysis of and have also been used to in the of and with (Furness et al. 2006). have we from this of the devices on seabirds revealed their the underwater of diving birds and the long-range travel of depth and the depths and by penguins are m and in et al. 2007), as as by and in 1989, and Similarly, tracking studies of and made us the of their global foraging (Weimerskirch and Wilson 2000, Croxall et al. 2005, Phillips et al. 2005, Shaffer et al. 2006, González-Solís et al. 2007), km; Fig. and rapid flight km in with a Weimerskirch et al. 2000, Murray et al. 2003, Catry et al. 2004a). strategies and profiles have now been for most penguins species at colonies and ocean and for many and species (reviews by 1989, Boyd 1997, et al. 2006, et al. 2006). of logging devices have revealed of underwater depth and sensors that the of oxygen to diving and can this in to the depth (one for m in or of prey they to catch a is (one for every four (Wilson 2003, Ropert-Coudert and Wilson 2005). Time-depth recorders and temperature and loggers have and of diving (reviews by 1989, Boyd 1997, Butler 2004, et al. 2006, et al. 2006). in temperatures to be adaptations for underwater foraging in penguins and cormorants (Wilson and Grémillet 1996, Bevan et al. 1997, Handrich et al. but were not in a et al. 2007). telemetry has been in and the and long foraging from the colony in several among the and penguins (e.g., Weimerskirch et al. Ropert-Coudert et al. 2004). several only a to body that are the (Weimerskirch et al. to to typically body mass and more food on than on long (Shaffer et al. 2003, Weimerskirch et al. Ropert-Coudert et al. 2004). The for on the be to foraging activity (Shaffer et al. 2001) or in the use of wind patterns (Weimerskirch et al. and tags have been used to the of individuals to foraging and the roles of memory and among seabirds in in the and range of long-distance by Croxall et al. by breeding Grémillet et al. Hamer et al. 2007), and by breeding Irons the use of and the of memory in pelagic Red-footed Boobies (Sula sula) foraging for prey in tropical waters not to the foraging in but generally in the where might (Weimerskirch et al. devices have greatly our of how seabirds food at tracking data have revealed patterns of area-restricted behavior, identified using techniques like first time and 2003, and Weimerskirch 2005, et al. 2006), et al. and et al. 2007). These techniques researchers to the location, and of from birds' Similarly, analysis and have of high use by tagged seabirds (e.g., et al. 2000; et al. Phillips et al. 2005, 2006). of high or it is to the or associated with each to habitat or to that habitat et al. and Weimerskirch 2005, Weimerskirch et al. Phillips et al. 2006, Shaffer et al. 2006, et al. 2006). and of seabirds outside the breeding is but the of and birds has significant and and can be of or (Furness and Camphuysen 1997, Boyd et al. 2006). birds can provide essential information on to conditions among species and by and within species et al. 2006, et al. 2007). and are increasingly providing information on at sea (e.g., Croxall et al. 2005, Phillips et al. and on the wide-ranging movements of birds (e.g., Phillips et al. 2005, Shaffer et al. 2006, González-Solís et al. 2007, et al. 2007). tracking that the global of in a in the et al. and identified and remote of species in the et al. 2006). This is essential for monitoring the on and marine birds of changing sea such as and and from and in devices have revealed and in foraging strategies and in many a in diving to have been in two species and larger and for than et al. et al. and in the costs, direction, and flight speed of foraging have also been for several species of (e.g., Weimerskirch et al. Shaffer et al. 2003, Phillips et al. and et al. 2005, Weimerskirch et al. information us to the and of the and it also and their exposure to anthropogenic like et al. and (Weimerskirch et al. and 1999). The on birds of attached or implanted devices cannot be for and because the devices the being measured (Wilson et al. 2002a, Wilson and 2006). of devices to be on the and on the body and on the foraging used by birds (e.g., diving of tags is also a because the of a small for a long time is likely to from that of a for a birds and pursuit are most likely to show of either implanted or attached devices the study on by et al. can diving foraging or effort, and of colony and of future (Wilson et al. 2002a, Phillips et al. 2003, Wilson and 2006). to and implanted a wide range of with implanted devices et al. et al. et al. et al. 2007). The of tags on breeding birds can be to their in the of et al. or to a that a of et al. 2004). With and devices have been on larger and with (e.g., Phillips et al. 2003, et al. 2006, Hamer et al. 2007), some only changes (e.g., Weimerskirch et al. and many not the of We researchers to to the of their devices and to for when interpreting and we to on the of this information in We also researchers to provide to on in tag design and attachment to on birds. is a limitation of satellite telemetry and data loggers, in can the to statistically and because of sample (Ropert-Coudert and Wilson 2005). to the Argos system can per day per tag and, hence, a on studies that require large sample or track birds as consumer for miniaturized communication and more and satellite these systems will become more Seabirds sensors have the to become tools for oceanography (Wilson et al. studies of seabirds have made major the and of prey species in marine in and and the of to changes in physical marine et al. 2006, Piatt et al. 2007). The addition of satellite telemetry is greatly of ocean et al. 2006). seabirds are to provide unprecedented insights into physical and biological ocean in time as ocean Seabirds are among the most mobile and information on their location tracking coupled with will information on ocean do not sample their in a or but are most associated with ocean such as and and et al. 1999). These are usually the systems that are of to and and temperature sensors on their can provide widespread and information on sea which be valuable in and the widely used satellite (Weimerskirch et al. 1995). that tags can provide more of satellite than et al. sensors will likely provide information on sea a used to water masses that is impossible to from or aircraft. This technology is in use by researchers study and temperature profiles the sea using as (e.g., et al. 2007). we seabirds sensors for or ocean providing essential information at a of the of to the and seabirds that most of their on the high seas are that these birds and rapidly pass many and of their foraging and essential for global and of this information is from or (e.g., et al. 2007, et al. 2007), but these are usually to or waters and all the data usually to and management or marine et al. are not for most of oceans et al. 2006). Data from satellite tracking and data loggers are to conservation and for the wide-ranging and (e.g., 2004, 2006). of and management the conservation and management application of devices is to where and when birds might be to such as and from devices are valuable in these risks to species such as the et al. 2006, 2007). of foraging is also essential in the or management responsible for with 2004, 2006; et al. 2005; Phillips et al. 2006; et al. 2007). 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