INTRODUCTION

Fauna is one of the most important features of our planet. Humans and animals share the habitat. Animal behavior can serve as an indicator of man’s influence on nature and changes in natural systems. Billions of animals are constantly migrating around the globe. They connect the most remote and inaccessible regions on Earth and in the oceans and can be a kind of indicator for assessing the well-being of our planet.

The very existence of animals, their vital activities, emergence and extinctions of species have a huge impact on the natural world in its present form. V.I. Vernadsky’s concept on the biosphere is based primarily on the theory of biogenic migration [1], which is based on observations of global movements of animals and their efforts to populate our planet to the maximum [2]. It has always been so, and we can expect it to remain so in the future. The impact of humans on nature affects the behavior of animals. The reason for this is that all biological species have special niches best suited for their existence. If they lose some or all of such niches as a consequence of human activities, a population shrinks or dies out or changes its behavior and seeks a new habitat, which can serve as an early indicator of human-caused environmental change. Animals are essential to our existence, but at the same time, they play an increasingly important role as carriers of diseases and epidemics. About 70% of the world’s epidemics–SARS, West Nile virus or avian influenza–are infectious diseases caused by interactions between wild animals, farm animals and humans.

It should be noted that the process of animal migration itself raises many questions. For example, migrating birds perform long flights, including those over seas and oceans. This fact suggests that they have an innate ability to orientate and navigate, but exactly how this works is not yet clear.

In order to understand how exactly an animal navigates in space and determines its heading, we should find answers to the following fundamental questions. Where is the animal at any moment of its life? How is it feeling? What is it doing at the current moment in time? What causes its death?

As for animals living in the natural environment, none of these fundamental questions can yet be answered when it comes to mean and long periods of time, especially in the case of small animals that are most important to us, for example, as carriers of disease (primarily bats).

In times of significant global changes, it is of crucial importance for humans to identify and use biological indicators of climatic and environmental changes. Wild animals that live in a wide range of climatic zones all over the world and migrate between them are ideal objects for this purpose.

Currently, satellite technologies for global monitoring and tracking of animals do not cover about 75% of birds and mammals because they are small in size. About 30 years ago, ornithologists pointed out great prospects for using miniature satellite radio beacons to study bird migrations [3]. Many ecologically and economically important species of animals are very small, such as bats, songbirds, and migratory locusts. A general rule in studying animal migration is that the devices attached to them should not exceed 3% of their body weight so that the extra weight does not affect the natural behavior of the individual [4–6]. The current challenge is to create a system for global monitoring of small animals, their movements, which will open a new era of research in this field of knowledge [7].

The ISS is a convenient laboratory to continue the development and to test systems for tracking animal migrations in practice, primarily because the station flies at an altitude of about 400 km, while artificial Earth satellites work at higher orbital altitudes. In addition, the presence of a crew on board the ISS makes it possible to mount large structures and antennas on its outer surface, so that the size of transponders on Earth can be reduced. It is also important that Russian specialists developed a unique technology for successful experiments on orbital stations and have gained considerable experience in it [8, 9]. Both this experience and technology are used aboard the ISS RS, in particular, in the URAGAN experiment, the purpose of which is to test and upgrade the equipment and technologies for studying the Earth and assessing the state of potentially dangerous and catastrophic phenomena [10].

It was in 2009 that the development of a system for tracking small animals started at the initiative of the Max Plank Institute of Animal Behavior (MPIAB, Germany) within the ICARUS program headed by Professor M. Wikelski, an enthusiast and the leading world expert in the animal migration studies. Professor M.Yu. Belyaev, the scientific leader of the URAGAN space experiment, proposed to test such a technology and system aboard the ISS RS [4, 5]. This decision was motivated by the coincidence of the tasks to be solved within both lines of research, as well as the available facilities allowing new technologies and scientific equipment to be tested aboard Russian orbital stations [11, 12]. As a result, in November 2014, the space agencies of the two countries signed the Agreement, whereupon the project started and the ICARUS scientific equipment was developed and delivered on board the ISS RS [5, 6].

The ICARUS scientific equipment is a system comprising onboard and ground-based segments. The onboard equipment includes a control computer OBC-I (OnBoard Computer ICARUS) and an antenna assembly, which provides outputs of control data to the sensors (tags) attached to the animals, as well as collects data from the tags on the coordinates of animals moving during their seasonal migration. Functioning of the ICARUS onboard equipment was provided due to the received data and ISS RS systems [13]. In accordance with the Agreement, the German space agency DLR (Deutsches Zentrum für Luft und Raumfahrt) was responsible for the antenna assembly and the control computer. It should be noted that the success of this project was facilitated by fruitful cooperation between German and Russian specialists. For example, based on the extensive experience in designing onboard antennas, the Russian specialists proposed an effective scheme and design of the onboard antennas for the ICARUS equipment, which was implemented in the ISS RS [5, 6, 14]. The Electronic company Elkus (St. Petersburg) created and produced the OBC-1 control computer; earlier, Elkus developed an OBC for the German experiment Rokviss carried out at the initial stage of the ISS deployment. The OBC was easily integrated with the ISS RS onboard systems owing to a special power supply unit and the control and information interfaces. The OBC control computer worked successfully in the Rokviss experiment, and then it continued working in the joint Russian-German Kontur and Kontur-2 experiments for a long time [15]. Due to the positive experience of cooperation between the German and Russian specialists gained in the Rokviss experiments, the German company STI, responsible for the ground-based part of the ICARUS equipment, decided to involve Elkus to create OBC-I. The software for that computer was developed by STI.

The ground-based part of the ICARUS equipment includes tags that are attached to the migrating animals, as well as special control and data processing complexes [4–6]. A miniature tag, which weighs less than 5 g, makes it possible to communicate with onboard ICARUS equipment at a distance of up to 600 km. The tag uses an application-specific integrated circuit (ASIC), which performs the main functions of a transmitter. The ASIC is optimized for low power consumption: the main power consumers are RF communication and navigation systems. The tag contains a U-blox EVA-M8M multi-system navigation module (Switzerland), which has high performance and sensitivity and uses information from the GPS, GLONASS, Galileo, and BeiDou. The chip is in a QFN-type package with planar pins placed directly under the chip on all four sides. The module dimensions are 7×7×1.1 mm. The tag receives information on orbit and attitude from the ISS, and it can calculate data about possible communication sessions with the space station. At the calculated time, the tag uses a satellite navigation system to determine its location and transmits this information to the ISS RS, along with data on accelerations, pressures and temperature, as well as those from a magnetometer, which is also included in the tag. The information received at the station is transmitted to the Moscow mission control center (MCC-M), where it is preliminarily analyzed and then provided to the research participants [4–6]. The service life of the tag is no less than 9 months.

The commissioning tests of the ICARUS system started in March 2020; in September 2020, the pilot operation phase began, which successfully ended in 2021 with its transition to the animal migration tracking mode. Dozens of important studies over performed over that time. For example, the migration of blackbirds, cuckoos, owls, saigas, wild boars, and many other species of mammals and birds were studied under the Russian scientific programs. In addition, tags were installed on mountain slopes of the Caucasus in order to assess the feasibility of performing monitoring of dangerous landslides [16, 17].

TESTS AFTER DELIVERY AND INSTALLATION OF THE EQUIPMENT ON BOARD THE ISS RS

From March 10, 2020 to September 14, 2020, a group of Russian and German experts tested the ICARUS equipment in accordance with the test program approved by both sides.

The tests were aimed to check the operability of the ICARUS antenna after it was installated on the outer surface of the ISS RS service module, electrical and data/logic interfaces between OBC-I and the ISS RS onboard systems, and interaction between the ICARUS antenna and ground-based equipment.

The program included five tests. From March 10, 2020 to April 05, 2020, Test 1 was conducted in autonomous mode, during which the state of the ICARUS hardware was monitored, and fresh measurements were compared with those obtained in ground tests.

Test 1 consisted of two parts that were conducted in parallel: background radio noise detected by the ICARUS receiver in different areas of the Earth was registered and analyzed, and the receiver was fine-tuned. At the same time, the downlink energy balance was tested at different levels of the transmitter power (3.2, 4, and 5 W). The antennas installed on the roof of the Company STI in Immenstaad, Germany, were used in Test 1 to receive and transmit signals (see Fig. 1).

Fig. 1.
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An antenna assemply used to exchange information between the ISS and ground facilities in Test 1.

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During the tests, the OBC-I received the following information from the ISS RS onboard systems:

• ballistic data on the ISS orbit;

• ISS attitude data;

• the ISS onboard time and sync pulse (PPS);

• two-line elements (TLE) in the NORAD and NASA format, widely used for Internet representation of ballistic information on objects in near-Earth orbits [18].

Measurements of the ISS RS autonomous navigation system were also used to obtain the above information [19].

As a result, all the data on operability of the ICARUS onboard systems were within the expected values. In particular, the values of temperature, voltage and current were the same as those observed during the ground tests. Minor malfunctions were promptly corrected by commands from Earth. The ICARUS onboard equipment was found to be in proper operating condition in concordance with its specifications.

During the test, the Earth background radio noise was recorded in the frequency range of the ICARUS receiver from 468.065 to 468.135 MHz at different settings of attenuation in the receiving antenna channels A, B, and C, which made possible global maps of radio noise (Fig. 2). In Fig. 2, green, yellow, and red colors show the low, increased, and high levels of radio noise, respectively. The generator’s local phase-locked loop (PLL) frequency of 388.75 MHz proved to be the optimal one.

Fig. 2.
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The Earth background noise (PLL frequency 388.75 MHz), attenuation in Chanels А, B, and C—12, 12, and 11.5 dB, correspondingly.

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According to the test results, the ICARUS equipment worked in the most efficient way when the internal attenuation settings in the receiving antenna in channels A, B, and C were, correspondingly, 10.5, 12, and 10.5 dB.

The ICARUS downlink signal was analyzed by the experts, who found that it propagated properly, without any distortion.

Based on the test results, the carrier frequency of the transmission channel was decreased by 1500 Hz, and the transmitter power of 3.2 W was chosen as optimal.

Test 2 was conducted in autonomous mode from April 7, 2020 to April 29, 2020. It was, in fact, an Uplink Pattern Test aimed to check the signal transmission from Earth to the ISS using the test antennas installed on the roof of the STI and the tag simulator placed inside it, and, primarily, to get patterns of the ICARUS receiving antennas on the ISS RS in order to precisely determine the directions of the main beams and beam widths of the receiving antennas, as well as analyze the signal RF spectrum with respect to the signal reception frequency (402.25 ± 4.5 MHz) (Fig. 3).

Fig. 3.
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The signal spectrum recorded while the ISS was passing over the STI ground station.

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The tag simulator was a portable computer with a GPS receiver and antenna. The computer was also connected to the test antennas to generate RF signals required in the tests of the onboard ICARUS receiver. The signals transmitted to the ISS were specifically precalculated for each test and recorded into the computer memory according to prescribed scenarios.

According to the program, Test 2 was supposed to include twelve communication sessions to be held while the ISS was flying over the Immenstaad ground station. The aim was to precisely determine the pattern of four–three uplink and one downlink–communication channels.

It was planned that measurements were to be taken for each of the receiving channels (left, right, and central) during four passes of the ISS. From the receiving antenna, the signal was fed to the OBC-I via three high-frequency cables, then, via the Russian data transmission channel, it reached the MCC-M, and finally it was transmitted to the STI.

In Fig. 4, the calculated patterns of the receiving antennas are shown in blue, while the pattern representing the maximum downlink data transmission from the onboard antenna, in green.

Fig. 4.
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The calculated patterns of the ICARUS receiving and transmitting antennas.

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A preformed test signal with a bandwidth of 2 MHz was used to transmit a signal from Earth to the ISS RS. Its spectrum center was at a frequency of 402.25 MHz. The signal was transmitted using a tag simulator, power amplifier, and the ISS tracking system. The calculated equivalent isotropic radiated power, EIRP, of the uplink was 36.1 dB mW.

Eventually, thirteen sessions were held in Test 2 while the ISS was flying over the Immenstaad ground station. For each session, the STI experts prepared a raw-data-dump activation command (2 GB) after the communication session was over.

The uplink data proved to be in full agreement with the results of simulations and ground tests.

The recorded uplink pattern was used to determine the actual location of the receiving time window and compare it with the predicted time. The margins in the location of the receiving window were primarily due to the errors in determining the ISS attitude and time. It was found that in reality, the location of the receiving window appeared 2–3 seconds later in the flight direction relative to the predicted one, which was within the acceptable tolerance and did not affect the data transmission from the tag. Based on the results of Test 2, the communication time with the ISS was corrected so that the signal from the tag reached the ISS with its maximum power. Test 2 showed that the docking/undocking facilities of the US orbital segment (USOS) of the ISS and the USOS extravehicular activities affected the operation of the ICARUS equipment since they caused noise in the uplink channel. For this reason, during docking and undocking operations in the ISS USOS, the ICARUS equipment was switched over from the normal ON mode to HEATING mode.

From May 26, 2020 to June 26, 2020, Tests 3 and 4 were performed simultaneously in autonomous mode. The first of them used the STI tag simulator; in the second one, the test tag was used. The general view of the test tag is shown in Fig. 5.

Fig. 5.
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The test tag.

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The test tag was not a prototype of the real tag, which was supposed to be attached to birds and animals, but it had similar software for communication and standard interfaces so that it was possible to control the test tag via a portable computer and connect it to different types of antennas.

Various data transmission scenarios were simulated, with different time intervals of data packet transmission and signal power. As a result of the tests, the characteristics of the system ensuring stability of data reception and transmission were determined.

From July 13, 2020 to September 14, 2020, Test 5 was performed in autonomous mode. It was aimed to check how the ICARUS equipment worked with prototype tags placed in conditions close to real ones. Since the coordinates of the tags were known, it was possible to estimate the navigation accuracy of the system, which proved to be close to the accuracy of the GPS and GLONASS. During the test, the Russian experts used ten tag prototypes, including those with minor software modifications.

Below are some of the main conclusions based on the results of Test 5:

• all prototype tags had communication with the IСARUS equipment installed aboard the ISS RS. Navigation data and all information from the tags were received in Moscow MCC-M via the ISS RS telemetry channel, and then it was available for the participants of the experiment;

• During Test 5, the ICARUS equipment did not receive any other signals except those coming from the prototype tags;

• the tag location had a significant impact on the charge of its battery and the probability of its contact with the ISS. The batteries of the tags located in the forest or under a tree were completely discharged after a certain time, whereas in areas with sufficient sunlight, the batteries maintained a normal level of charge.

The results of Test 5 were taken into account during the operation phase.

Thus, the onboard ICARUS hardware and tags were successfully commissioned between March 10 and September 14, 2020 with the participation of RSC Energia, STI, and INRADIOS (Dresden, Germany), as well as MPIAB and the Institute of Geography, Russian Academy of Sciences (IGRAS). It was found that the operation of both the onboard ICARUS hardware and the prototype tags was consistent with the technical documentation.

SOME RESULTS OF THE ANIMAL MIGRATION STUDIES

After the tests were successfully accomplished, a global study of animal and bird migrations began. Projects that were set up by Russian scientists at the first stage of the research are shown in the table below.

Table 1. Projects of Russian scientists
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In 2021 studies of bird migrations conducted under the Russian research program with the use of the ICARUS equipment installed on the ISS RS pursued the following three main goals:

• to study migration routes, stopover sites and wintering grounds of rare species included in the Regional and Federal Red Data Books (peregrine falcon, Eurasian curlew, Asian dowitcher, and great snipe);

• identify bird species that are potential spreaders in avian influenza and other epizootics in the Asian part of Russia (Oriental turtle dove, waders, and predator birds);

• study the influence of natural (climate change, weather, geographical barriers) and anthropogenic (human transformation of landscapes) factors on the phenology of migrations, changes in flyways and wintering grounds, as well as bird dispersal in the 21st century (blackbird, Arctic tern, predator birds, and cuckoos).

STUDY OF RARE SPECIES

The Eurasian curlew is an isolated, narrow-area subspecies of the widespread large curlew. Its habitat and numbers have been declining over the past 20 years. Breeding places of this subspecies are currently known in general outline; the borders of this species areal are still unknown, information on wintering sites is very scarce, and migration stopover areas are not known either. Their numbers are low and continue to decline everywhere in breeding areas. The reasons for this are not clear: whether they lie in breeding areas, flyways or wintering grounds. There is a real threat of extinction of these birds if no effective conservation measures are taken. The subspecies is included in the Red Data Book of the Russian Federation. In May 2021, three Eurasian curlews got the ICARUS tags in the Saratov and Orenburg Regions. Navigation data from the ISS RS provided information about the timing of their premigration movements and migration, migration routes, location of migration stopover sites, and how long they stay there, wintering areas, and the specific localization of the birds in the habitats. The information obtained for only three individuals showed that migration routes and wintering areas turned out to be completely different and previously unknown (Fig. 6) [20]. An important migration stopover was found on the lakes of the Kumo-Manych depression in the south of Kalmykia, where Eurasian curlews stayed for 2–3 weeks and from where their further migration routes diverged to the Black and Caspian Seas. The data obtained closed significant gaps in the knowledge about this rare bird and drew the attention of the Kalmykia environmental authorities to the migration stopover area. These data were also used in the latest version of the Red Data Book of the Russian Federation [20].

Fig. 6.
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Autumn migration routes of the Eurasian curlews detected with the use of the ICARUS navigation information of the ISS RS.

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The peregrine falcon is one of the most common species of predatory birds; it is not found only in New Zealand and Antarctica. At the same time, peregrine falcons’ habitat is unevenly distributed throughout its range, and their number is very low in most areas. In some places, this species has disappeared from the nesting area altogether, which was the reason for including it in the International Red Data Book and the Red Data Book of the Russian Federation [20]. Young peregrine falcons were tagged in July–August 2021 in the Nenets and Yamalo-Nenets Autonomous Okrugs. Both areas were significantly north of the tag signal reception area, which is why the first data were obtained 2–2.5 months later in more southern latitudes. Information from the ICARUS equipment on the ISS RS made it possible to determine the exact dates and migration routes of birds from breeding areas to wintering grounds, localize their stopover sites on migration routes; in addition, this information can be used to estimate the size of territories occupied by birds in different breeding periods depending on habitat types and seasonal distribution of their prey species.

The Asian dowitcher is a rare species included in the Red Data Book of Russia. Its number is estimated at 23 000 individuals. It nests in the forest-steppe and steppe zones of Asia and has a fragmented and dynamic habitat. It has been nesting in Yakutia since 2019 [21]. The flight routes and wintering grounds of the Yakutian population of this rare species are still unknown. The analysis of navigation data on the migrations of six birds has shown that the trajectory of the autumn migration passes through Eastern Mongolia and North-Western China to the coast of the Yellow Sea. The birds stayed in China for about a month and then headed to different areas–Vietnam, Thailand, and Indonesia–for wintering (Fig. 7) [22].

Fig. 7.
figure 7

Migration routes to the wintering grounds of the Asian dowitcher identified from the navigation data of the ICARUS equipment of the ISS RS.

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Individual data on movements of the birds will make it possible to develop a protection strategy and locate the most important habitats of the Asian dowitcher in Russia and abroad.

The great snipe was a common and even numerous species in Moscow suburbs until the middle of the 19th century, but during the 20th century their numbers catastrophically decreased mainly due to destruction of their original nesting sites, namely, draining and destruction of bogs, plowing of meadows, etc. As a result, since 1998, the breeding population of this wader in the Moscow Region has been included in the Regional Red Data Book. In 2021, navigation information helped identify migration routes of great snipes to their wintering grounds and potential threats during their migration. Eight of ten great snipes that were ringed in breeding areas of the Northern Moscow region that season migrated to Africa for wintering. Half of the ringed birds died during migration over desert areas, and the other four died when they were flying over the Sahara in Egypt, southern Chad, and Sudan. At the beginning of March 2022, four birds were staying in Zambia and Congo [23], and in May, at least one of them returned to the area, in particular, to the same site where it was caught and ringed in 2021. Data on the migration routes of great snipes to their wintering grounds were submitted for inclusion in the Eurasian African Bird Migration Atlas.

STUDYING THE ROUTES OF INFECTION

Migrations of birds over the mountains and deserts of East Asia are still poorly understood. The navigation information from the ICARUS equipment of the ISS RS provided data on the routes and timing for some bird species, long-distance migrants flying from Eastern Siberia to wintering grounds in Southeast Asia and Australia. Analysis of the migration strategy of the Japanese sparrowhawk, Swinhoe’s snipe, pin-tailed snipe, and oriental turtle dove tagged in Transbaikalia [24, 25] has shown that these birds are unlikely to be able to carry highly pathogenic influenza strains from Southeast Asia to Siberia, because the acute phase of disease is incompatible with hundreds of kilometers of the migration rushes recorded for these species according to information from the ICARUS equipment.

INFLUENCE OF NATURAL AND ANTHROPOGENIC FACTORS ON BIRD MIGRATIONS

The study of migrations of Arctic terns based on observations of ringed birds aims to find out the details of migratory routes and features of their ecology with the help of the latest technologies. The fieldwork area was located on the Onega Peninsula of the White Sea at latitude of 65.15°, which is much to the north of the communication zone with the ISS. The ICARUS tags were attached to the birds at the beginning of the breeding season, so the first communication with the ISS was established in the second half of August, at which time birds had already migrated south and were found in the middle of the North Atlantic. New data were obtained on the migration routes of this species: after nesting on the White Sea coast, contrary to expectations, instead of flying south to the wintering grounds in the Antarctic, the terns stayed for 2–3 weeks north of the breeding site, near the ice edge in the Greenland and Barents Seas (Fig. 8) [25].

Fig. 8.
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Migratory path of the Arctic tern in the Northern Hemisphere.

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This unusual direction of the first part of the migration was most likely caused by a lack of food in the nesting area. Before a long flight to the Southern Hemisphere, especially over the poor tropical waters of the Atlantic, terns must have sufficient reserves of fat; this is the reason why before their migration to Antarctica, they fly more than a thousand kilometers north to the rich waters at the edge of the perennial ice and ice shelves. Further warming in the Arctic will result in the disappearance of perennial sea ice, most of the ice shelves, and the impoverishment of the adjacent waters. It can be assumed that this will have a negative effect on seabirds, including the population of Arctic terns nesting not only in Arctic latitudes, but also 1500 kilometers south of these areas.

CONCLUSIONS

The tests conducted in the frames of the research program implemented onboard the ISS RS and the results obtained in the studies of animal and bird migrations using the ICARUS equipment have confirmed the effectiveness of the onboard migration monitoring system. Creation and operation of this system have shown the feasibility and potential of using the ISS RS as an orbiting scientific laboratory for testing new technologies, which is one of the goals of the URAGAN experiment. The global system for monitoring the movement of objects can be used to address important scientific and applied problems. Using the whole complex of the equipment provided by the URAGAN experiment aboard the ISS RS offers great opportunities for studying migrations of animals and birds [10].

Data on animal migrations are not just a description of the pathways of birds and mammals, but unique information about their interaction with the environment [26, 27]. Thus, the hardware provided by the URAGAN experiment makes it possible not only to monitor the moving animals of interest, but also to try to find out the reasons for changing the routes of their migrations and wintering sites. The created system will also allow deeper insight into the nature and mechanism of orientation and navigation of migrating birds [28–30].

The information obtained owing to the ISS RS ICARUS navigation system helped identify the most important migration stopover sites and new wintering grounds of rare bird species, which served as a basis for recommendations on their protection strategy. New data on migrations of Far Eastern birds allowed identifying types of potential carriers of especially dangerous natural infections. Information was obtained about unusual migration routes of Arctic birds and the possible impact of anthropogenic activities and global warming on them.

This technology can also be used to predict dangerous and catastrophic events, such as earthquakes, the spread of various diseases, etc. [6, 31]. It will also be useful for monitoring of dangerous glaciers, landslides, etc., in the framework of the URAGAN experiment carried out in the ISS RS [16, 17].