A lifetime track of a griffon vulture: The moving story of Rehovot (Y64).

Abstract

24th of August 2013. The day started as any other capture day in the Negev desert, Israel, with 36 griffon vultures (Gyps fulvus) waiting inside the capture trap operated by the Israeli Nature and Parks Authority (INPA). They were about to be released back to nature after receiving a wing tag, and, for a few chosen ones, also a GPS transmitter (Iezekiel et al., 2003). One of these vultures, later named Rehovot, was merely a few months old when he received his first nickname: Y64 (the number of the wing tag). Rehovot, a young male weighing 8.3 kg, was to become an important sentinel for his species. Rehovot was fitted with a 90 g GPS–GSM transmitter (by e-obs telemetry; https://e-obs.de/), attached using a Teflon ribbon harness, in a backpack configuration (Harel, Horvitz, et al., 2016). The transmitter Rehovot carried on his back provided 8 years of data (Figure 1; Acácio, Anglister, et al., 2022), contributing with crucial information for vulture conservation (Efrat et al., 2020; Spiegel et al., 2015) and, coincidently, also to his own survival. This case study highlights the importance of long-term movement research in understanding how animals explore and interact with their environment, and how this can be used for species conservation (Nathan et al., 2022). Across the globe, vulture populations are collapsing, mostly due to poisoning (Green et al., 2004; Ogada et al., 2012). In Israel, griffons are critically endangered and have experienced a fast population decline. Records from the late-1800s to mid-1900s show that griffons were a common resident in the region (Hardy, 1946; Tristram, 1865), but the population declined to ~400 griffons two decades ago, and to only roughly 200 individuals today (Hatzofe, 2020). To prevent the local extinction of this species, the INPA runs an extensive management program, providing contaminant-free food in supplementary feeding stations, releasing captive-bred griffons, and individually tracking vultures with GPS transmitters (Harel et al., 2017; Spiegel et al., 2013). These transmitters typically last between 1 to 4 years, unlike griffon vultures who can live up to 30 years in the wild. Although the GPS transmitters only track a short period of the griffon's long life, they have been instrumental in studying vulture ecology, including their habitat use and foraging requirements (Alarcón & Lambertucci, 2018; Duriez et al., 2019). Real-time GPS tracking is particularly crucial for the detection of poisoning events: whenever the GPS informs that a vulture is either moving very little or is suspected to be dead, an INPA ranger is immediately sent to the field to investigate (Hatzofe & Vine, 2019; Nemtzov et al., 2021). That is exactly what happened with Rehovot. In his first year of life, Rehovot often moved more than 30 km away from the roost, and some days he even flew more than 100 km (Figure 2). Despite staying mostly in the Negev and Judean deserts, Rehovot also visited southern Israel (Eilat), the eastern Sinai (Egypt), and Jordan. But, on the 16th April 2015, 2 years after fledging, the GPS showed that Rehovot had not flown for more than 24 h. He was close to the ruins of an ancient Nabataean city (dated from the 1st century BCE to 5th century CE) known as “Rehovot in the Negev.” Thanks to this proximity, the vulture was named after the ruins: “Rehovot.” A ranger (Amiram Cohen) responded quickly, found Rehovot in a very poor condition and rushed him to the Israeli Wildlife Hospital (https://www.wildlife-hospital.org.il/en). An initial inspection revealed that Rehovot had lost weight (weighed 7.7 kg), had a very weak heart rate, and was vomiting and barely keeping his head up. Under the care of Dr. Nili Anglister, Roni Elias and, particularly, Shmulik Landau (who checked him every 15 min over the first, and most critical, night), Rehovot received the appropriate treatment. The following day, another GPS-tracked vulture, an adult female (at least 11 years old) named Faculta (currently T15 wing tag) was also collected from the same location and entered the hospital in a very weak state. Both vultures were diagnosed with methomyl poisoning, an insecticide used for a variety of crops as well as to deliberately poison wildlife (Plaza et al., 2019) and, in this case, used illegally to bait a carcass for culling feral dogs. As this was the middle of the vulture breeding season and Faculta was known to be nesting, it was imperative that she would be released quickly: the longer Faculta was absent from the nest, the higher the probability her chick would perish. Thanks to the swift and efficient treatment of the hospital staff, both vultures were released on the 19th of April (i.e., within less than 3 days), and both Rehovot and Faculta, as well as her chick, were to survive this poisoning incident (Figure 2D shows Faculta on the nest with her chick, after recovery). After the poisoning event, the movements of Rehovot were tracked for another 6 years (Figure 1). While on some days he was still moving as much as 70 km away from the roost, Rehovot became more and more local as he aged. This was also reflected in the distances moved between consecutive night roosts: in his first year of life, Rehovot moved on average 11 km between roosts (SD = 17 km, maximum = 85 km), while in his eighth year of life, Rehovot mostly occupied the same areas and only moved on average 5 km between consecutive night roosts (SD = 10 km, maximum = 38 km) (Figure 2). Occupying smaller ranges as an individual ages is a common trend in griffon vultures (and several other species; e.g., Kane et al., 2022). Food is plentiful in Israel thanks to the large quantities of contaminant-free food provided by the INPA in several supplementary feeding stations for vultures (Duriez et al., 2022), thus reducing the risk of poisoning and allowing vultures' foraging movements to be quite local (Spiegel et al., 2013). While such long-term tracks of free-ranging animals are still rare, they have the potential to show, on a broad scale, how space use changes seasonally and throughout an animal's lifetime (e.g., foraging or roosting behavior; Harel, Duriez, et al., 2016; Spiegel et al., 2015). In endangered species, the age structure of the population may change as the population decreases (Jackson et al., 2020), which, if combined with age-specific space use (Weimerskirch, 2018), may regulate the ecosystem services the species provides (e.g., nutrient transport; McInturf et al., 2019 or, in the case of vultures, sanitation services; Fernández-Gómez et al., 2022). On a finer scale, Rehovot's data also allowed the study of age-related changes in flight behavior and their fitness implications. In fact, Rehovot was selected for GPS tracking exactly for this purpose, as a part of Roi Harel's PhD studies at the Movement Ecology Laboratory, at the Hebrew University of Jerusalem. Together with other vultures, Rehovot's flights were tracked at high resolution, recording GPS position and altitude every 1 s for a few consecutive days (Figure 3). Harel's study revealed that adult vultures outperform juveniles (including Rehovot) in utilizing rising air currents (commonly named thermals), as juveniles are yet to learn how to efficiently circle in the thermals when drifted by the winds (Harel, Horvitz, et al., 2016). This study provided a unique example of how detailed movement data can be used to identify specific tasks that young animals need to learn to improve their functional performance. Furthermore, understanding how animals utilize the atmospheric conditions to sustain flight allows the estimation of the energetic costs of movement (Harel, Horvitz, et al., 2016), and can also provide information on the risks of collision with human infrastructures, such as wind turbines (Péron et al., 2017). Nevertheless, such high-resolution tracking may come at a price. High temporal GPS tracking data increases the accuracy of the locations (Acácio, Atkinson, et al., 2022), but it may also fatigue the battery and overall decrease the lifespan of the transmitter. Thus, selecting the correct GPS schedule to fit the study's objectives is crucial. For example, in order to quickly identify vulture poisoning events is essential to have GPS locations at an intermediate temporal resolution (e.g., at least a GPS location every 10 min) and frequent GSM transmissions per day (Hatzofe & Vine, 2019; Nemtzov et al., 2021). The moving story of Rehovot came to an end on 14 July 2021, when the GPS showed no movement for several days. Due to the inaccessibility of the area, it was not possible to confirm if Rehovot had perished or if he had only lost his GPS transmitter. Overall, Rehovot was followed for 8 years and provided more than 1 million GPS positions. In the end, as it was not possible to confirm if Rehovot had died, one can still hope to find him someday soaring on the strong desert thermals, or even to recapture him and continue to follow his movements throughout the rest of his life. In summary, Rehovot's story illustrates how lifetime tracks can advance ecological research while directly promoting species conservation. Nonetheless, these long-term studies are challenging to maintain, partly due to technical difficulties (e.g., the lifespan of the GPS transmitters), and to the difficulty of obtaining uninterrupted funding, as these studies usually exceed the duration of research grants. Yet, only such individual and lifelong studies can unravel how behavioral and life-history patterns emerge in the wild, shaping species evolution and adaptation to their environment (Caspi et al., 2022; Wild et al., 2021; Wolf et al., 2007). For example, several studies have shown that adults differ from juveniles in a number of traits, from flying to socializing (Albery et al., 2022; Harel, Horvitz, et al., 2016). Yet, these comparisons often fail to identify the mechanisms through which the observed age-dependent patterns evolve. These differences can result from changes in individual behavior, either via learning, improvement, or senescence (Albery et al., 2022; Mueller et al., 2013; Sergio et al., 2014). In addition, differences can also reflect the selective mortality of individuals with particular traits (Sergio et al., 2014, 2022), emphasizing the value of individual long-term tracking. As the environment is changing faster than ever before, lifelong research is therefore fundamental to understanding if and how individuals adapt (or fail to adapt) to the challenges arising from human-induced environmental change (Caspi et al., 2022; Clutton-Brock & Sheldon, 2010). We dedicate this article to Shmulik Landau who was an inspirational caregiver at the Wildlife Hospital and is much missed. We also thank all volunteers and workers of the Wildlife Hospital for their dedication. We thank workers and rangers of the INPA for their work in the field, members of the Movement Ecology Laboratory at the Hebrew University of Jerusalem, and members of the Movement Ecology and Individual Behavior Laboratory at Tel Aviv University, particularly Assaf Uzan for logistic support. We thank Dr. Noa Pinter-Wollman, Dr. Nitika Sharma and Kaija Gahm for their feedback on the first version of the manuscript. Finally, we thank the editor, Professor John Pastor, Dr. Olivier Duriez, and two anonymous reviewers for the valuable feedback on the previous versions of the manuscript. Funding for this work was provided by the Binational Science Foundation (BSF) 822/2019 grant to Orr Spiegel, as well as BSF 255/2008 to Ran Nathan. Marta Acácio was supported by the George S. Wise Postdoctoral Fellowship (Tel Aviv University). Nili Anglister was supported by a stipend from Yad-Hanadiv. The authors declare no conflict of interest. Data supporting this research are sensitive and not available publicly due to the endangered status of the focal species in the study region; these data contain GPS locations of the focal individual and are available to qualified researchers via the Movebank study “E-obs GSM Vultures Israel” (Movebank ID 7359070; https://www.movebank.org/cms/webapp?gwt_fragment=page=studies,path=study7359070). An anonymized version of the dataset (Acácio, Anglister, et al., 2022) is available in Zenodo at https://doi.org/10.5281/zenodo.7413086 in which data were shifted a few kilometers from original locations to ensure the species safety, but maintains all the other geometrical attributes needed for reconstructing the analysis. Video S1. Video S1 legend. 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