Fifteen days are enough to estimate home-range size in some long-lived resident eagles

Morollón, Sara; Urios, Vicente; López‐López, Pascual

doi:10.1007/s10336-022-01982-5

Cited by 11 publications

(8 citation statements)

References 14 publications

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“…We trapped adults in the framework of an ongoing GPS tracking project aimed at studying mortality risks and eagles’ ranging behaviour in eastern Spain (more details in [ 28 , 29 , 30 , 31 ]). Adults were trapped from June to December during 2015–2022.…”

Section: Methodsmentioning

confidence: 99%

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Non-Invasive Sex Determination of Nestlings and Adult Bonelli’s Eagles Using Morphometrics

Estellés-Domingo

López‐López

2023

Animals

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Biometric analysis allows the sexing of most vertebrates, particularly birds. Birds of prey, and, especially, the Bonelli’s eagle (Aquila fasciata), show reverse sexual dimorphism (i.e., females are usually larger than males). In contrast to blood sampling, the use of morphometrics allows sex determination using a non-invasive method, and, therefore, it facilitates fieldwork. By means of a linear discriminant analysis of biometric variables, we obtained different equations that allow the sexing of nestlings and adult Bonelli’s eagles. We sampled 137 Bonelli’s eagles, 82 nestlings and 55 adults in eastern Spain during the period 2015–2022. The sexes obtained after linear discriminant analysis were compared with their molecular sexing. The validation procedure of the linear discriminant equations facilitated the reduction of the number of variables used and, consequently, optimised working time and sexing accuracy. After validation, some equations showed a 100% sexing efficiency for Bonelli’s eagles, particularly for adults. Our results showed that the variables with smaller overlap between the sexes were the lateral tarsus length and dorso-ventral tarsus length, particularly in nestlings. The rest of the variables showed some overlap between the sexes in both age classes. The results we obtained enable the sexing of juvenile and adult Bonelli’s eagles in the field using just these two measurements. Hence, this is an easy, accurate, quick and non-invasive method with multiple applications, including in studies on population dynamics, survival analysis or extinction risk assessments, which, ultimately, could contribute to the improvement of the conservation status of this endangered species.

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Section: Methodsmentioning

confidence: 99%

“…Once trapped, adults were measured, weighted and fitted with a GPS/GSM datalogger in a backpack configuration. This procedure took a maximum time of 30 to 40 min (more details in [ 28 , 29 , 30 ]).…”

Section: Methodsmentioning

confidence: 99%

Non-Invasive Sex Determination of Nestlings and Adult Bonelli’s Eagles Using Morphometrics

Estellés-Domingo

López‐López

2023

Animals

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“…We used the daily individual K50%, K75% and K95% isopleths computed with the whole tracked period from the following day after tagging to the end day of data transmission (e.g. animal's death, end of transmission), knowing that 15 days is the minimum tracking period to obtain a complete home-range (Morollón et al 2022).…”

Section: Home-range Analysismentioning

confidence: 99%

Home-range Size and Space Use of Territorial Bonelli’s Eagles (<i>Aquila Fasciata</i>) Tracked by High Resolution GPS/GSM Telemetry.

Morollón¹,

Urios²,

López‐López³

2022

Preprint

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The current advent of GPS/GSM technology, with high resolution GPS dataloggers available, provides information of the highest quality, which is certainly better than previous tracking methods such as ARGOS telemetry or conventional VHF ground-tracking. As a result, this has improved our knowledge of home-range behavior and spatial ecology of many species, including large raptors. In this paper, we use satellite telemetry information to assess the home-range size and the role of individual, year, sex and season (breeding or non-breeding season) in space use of the Bonelli’s eagle (Aquila fasciata). To this end, 51 territorial individuals (25 females and 26 males) were equipped with GPS/GSM transmitters and were tracked over a 7-year period (2015-2021) in eastern Spain. Overall, we recorded 4,791,080 fixes that were analyzed through kernel density methods (50%, 75% and 95% fixed kernels). Average home-range size according to the 95% kernel, 75% kernel and 50% kernel were 54.84 ± 20.78 km2, 24.30 ± 10.18 km2 and 11.17 ± 4.90 km2, respectively. The home-range size of individuals occupying the same territory was similar, mainly due to the cooperative hunting behavior exhibited by the species. No interannual differences in the home-range of the same territory were found, showing a strong territorial fidelity of the breeding pairs. Overall, females’ home-range size were smaller than males’ ones due to the decrease of activity in the breeding season due to laying, incubation and chicks attendance at nests. No seasonal variation in the general home-range size was found. Moreover, we found low neighbor overlap among territories (4,18% ± 3.06%) that evidences a high level of intraspecific competition in Bonelli's eagles. Finally, this study highlights the advantages of the use of accurate telemetry information to improve our understanding of the spatial ecology of the endangered Bonelli’s eagle, which ultimately will serve to better inform management actions for its conservation.

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“…In particular, since 2000, the Bonelli's eagle population has suffered a decline of 48.6% in the region, with an observed reduction of the breeding population from 31 territories occupied in 2000 to 18 occupied in 2022 39,40 . Specifically, in the south of this geographical region, video surveillance cameras were installed by the regional government in the latest two breeding seasons, in an area of high adult mortality 41 and where the recreational use of the environment for leisure activities has increased significantly in recent years, which has resulted in a significant increase in disturbance to wildlife in general and the endangered Bonelli's eagle in particular 42 .Since the year 2000, I have been collecting an annual monitoring database of the Bonelli's eagle population in the study area in which information on occupation, breeding performance and demographic parameters is systematically collected thanks to the combination of field monitoring techniques, bird ringing and telemetry information 39,[41][42][43] . Taking advantage of this long-term database, the objective of this work is to analyse the variation in the reproductive parameters of the Bonelli's eagle through a before-and-after control-impact (BACI) methodology 44,45 in territories in which video surveillance cameras were installed and in control territories monitored by field observation throughout the 23-years study period.…”

mentioning

confidence: 99%

“…Since the year 2000, I have been collecting an annual monitoring database of the Bonelli's eagle population in the study area in which information on occupation, breeding performance and demographic parameters is systematically collected thanks to the combination of field monitoring techniques, bird ringing and telemetry information 39,[41][42][43] . Taking advantage of this long-term database, the objective of this work is to analyse the variation in the reproductive parameters of the Bonelli's eagle through a before-and-after control-impact (BACI) methodology 44,45 in territories in which video surveillance cameras were installed and in control territories monitored by field observation throughout the 23-years study period.…”

mentioning

confidence: 99%

Potential negative effects of the installation of video surveillance cameras in raptors’ nests

López‐López

2022

Sci Rep

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Video surveillance cameras installed on birds’ nests are a cost-effective tool to study many aspects of ecology and behaviour that would otherwise be practically impossible to obtain. However, although most studies report neutral effects of cameras on birds, very few studies analyse in detail the potential negative effects of their use, particularly on raptors. Here, using a long-term database of a population of Bonelli’s eagle (Aquila fasciata) collected from 2000 to 2022, I show how the inappropriate use of video surveillance cameras could result in negative effects on the reproduction of a threatened species through a before-and-after control-impact study design. Pairs under video surveillance showed lower productivity, lower breeding success and unusual delayed laying dates. The installation of cameras close to the laying date, coinciding with the mating phase of individuals, most of them subadult inexperienced birds; in combination to the reiteration of visits to the nests once the cameras were installed to check the system, particularly during the incubation period and early stages of breeding; and the installation of cameras in a particular area subject to constant human disturbance, might explain these results. Potential management actions to mitigate the effect of the installation of video cameras on birds’ behaviour should include the need to plan the intervention dates, testing the systems beforehand under controlled conditions and adequate post-installation monitoring to avoid unnecessary disturbance to animals. Finally, I urge the scientific community to report the potential negative effects observed in their studies, especially if the target species are threatened with extinction.

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Fifteen days are enough to estimate home-range size in some long-lived resident eagles

Cited by 11 publications

References 14 publications

Non-Invasive Sex Determination of Nestlings and Adult Bonelli’s Eagles Using Morphometrics

Non-Invasive Sex Determination of Nestlings and Adult Bonelli’s Eagles Using Morphometrics

Home-range Size and Space Use of Territorial Bonelli’s Eagles (<i>Aquila Fasciata</i>) Tracked by High Resolution GPS/GSM Telemetry.

Potential negative effects of the installation of video surveillance cameras in raptors’ nests

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