Monitoring methods for the Golden Eagle<i>Aquila chrysaetos</i>in Norway

Gjershaug, Jan Ove; Brøseth, Henrik; Kleven, Oddmund; Kålås, John Atle; Mattisson, Jenny; Tovmo, Mari

doi:10.1080/00063657.2018.1478389

Cited by 6 publications

(7 citation statements)

References 16 publications

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“…Murphy et al, 2019). Documenting AFTS by such thinly spread field methods is inevitably delayed often through the timing of field efforts (Hardey et al, 2013;Hayhow et al, 2017;Steenhof et al, 2017;Gjershaug et al, 2018). Such field efforts provided important validation of our AFTS algorithmic approach; but were always later in confirmation than the algorithmic AFTS.…”

Section: Discussionmentioning

confidence: 99%

“…We used field observations to validate telemetric determinations of territory settlement through occupation. As a minimum, this required records of nest building activities involving a bird with a satellite tag (through visual confirmation of the tag's aerial) which was apparently paired with a partner within the territory in question (i.e., "territory occupation": Hardey et al, 2013;Hayhow et al, 2017;Steenhof et al, 2017;Gjershaug et al, 2018). Additional observations of breeding such as eggs laid, incubation behaviour, and/or chicks or fledgelings were also noted whenever possible ensuring minimal disturbance under licenced observations (Hardey et al, 2013).…”

Section: Field Validation Of Territory Occupationmentioning

confidence: 99%

“…When modelling population dynamics, first territory settlement represents recruitment of dispersing birds to the prospective breeding population (Azpillaga et al, 2018) which affects measures of occupied territories and a population's breeding productivity (Hayhow et al, 2017;Steenhof et al, 2017;Gjershaug et al, 2018). Age of first territory settlement (AFTS) is therefore an important variable in understanding several features of large raptor populations, not just NDD estimates.…”

Section: Introductionmentioning

confidence: 99%

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Age of First Territory Settlement of Golden Eagles Aquila chrysaetos in a Variable Competitive Landscape

Whitfield¹,

Fielding²,

Anderson³

et al. 2022

Front. Ecol. Evol.

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With life-history traits involving high survival, low reproductive output, years of natal dispersal and deferred maturity, the population ecology and behaviour of large raptors which occur at low densities can be difficult to study. The age at which large raptors first settle on a prospective breeding territory receives relatively little attention, but is a key metric in population modelling including, for example, projections of reintroduction projects. It can also be a barometer of the “health” of populations and the availability of breeding opportunities. The advancement of GPS-telemetry has proved invaluable in gaining insights into several aspects of large raptor ecology and behaviour. Age of first territory settlement (AFTS) is one such aspect. AFTS is important in modelling population trajectories and considering individuals’ lifetime reproductive success. We used an algorithm based on GPS-records from dispersing Golden Eagles tagged as nestlings in Scotland to estimate AFTS. While the lifespan of GPS-tags can bias against settlement dates of older birds, they can also potentially reveal settlement ages difficult or impossible to discern from other methods. We found a range of ages for AFTS, including those in their second calendar year; much younger than previously documented by other methods. Ground-truthing – when possible and if inevitably slightly delayed – confirmed territory occupation on field-based survey criteria. We found that eagles settled younger in vacant territories and when older in occupied existing territories. Birds’ sex had no effect on AFTS. Birds which dispersed earlier from their natal territory (indicative of “quality” from some previous research) had no association with AFTS. Our results indicate that within technological temporal limits GPS-data can provide for accurate and precise estimations of AFTS including early settlement not consistently or precisely recorded by other methods. Within our study’s variable competitive landscape we found that AFTS was associated with the availability of territorial opportunities but not with the timing of dispersal. These findings have consequences for studying and understanding large raptor population dynamics.

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Section: Discussionmentioning

confidence: 99%

Section: Field Validation Of Territory Occupationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Age of First Territory Settlement of Golden Eagles Aquila chrysaetos in a Variable Competitive Landscape

Whitfield¹,

Fielding²,

Anderson³

et al. 2022

Front. Ecol. Evol.

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“…The monitoring of Golden Eagle populations is done in many countries, and extensively in Scandinavia by both scientists and amateurs. In Norway, the methods of monitoring are mostly standardized to minimise bias (Gjershaug et al 2018). Active nests are easy to verify, but to be certain that an eagle pair is non-breeding will always remain a problem.…”

Section: Territorymentioning

confidence: 99%

Use of two distant nesting areas as a breeding strategy of Golden Eagles (Aquila chrysaetos) in Valdres, southeast Norway

Dunker¹

2021

Ornis Norv.

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Sixteen occupied nesting territories of Golden Eagle Aquila chrysaetos were studied between 2000 and 2020, in the southern part of the valley of Valdres, southeast Norway. Most of the study area consists of rolling hills dominated by spruce Picea abies with numerous clear-cuts. It was concluded that at least six (about 40%) of the eagle pairs in these territories move back and forth between two alternate, distant nesting areas 5.3 km apart (average). In two additional pairs, a second nesting area was considered possible. In the remaining eight, only one nesting area was found. The periods of one nesting area in use varied from 2–19 years, before moving to the other nesting area. This result was supported by panoramic mid-day surveillance of the air space between the two nesting areas during 2014–2020. The maintenance of a second core nesting area is most likely a strategy for moving to a more favourable hunting area and might be initiated by a new mate in the pair. The move might also be influenced by avoidance of a close neighbouring pair. A switch of nesting areas, as indicated by this study, could significantly affect results, when the number of eagle pairs in a certain area is counted. Cover photo: Golden eagle. Photo: Frode Falkenberg.

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“…Monitoring programs typically focus on the density and productivity of the breeding population, through monitoring of territories and nest sites (e.g. Derlink et al., 2018; Gjershaug et al., 2018; Jachowski et al., 2015; Katzner et al., 2020; Mabille et al., 2015; Tovmo et al., 2020; Tveraa et al., 2014; Watson, 2010). Diet varies widely both temporally and spatially in relation to availability, and golden eagles are both predators and carrion consumers (Katzner et al., 2020; Mattisson et al., 2017; Watson, 2010).…”

Section: Introductionmentioning

confidence: 99%

Estimating abundance in unmarked populations of Golden Eagle (Aquila chrysaetos)

Stien

Tveraa

et al. 2022

Ecol Sol and Evidence

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1. Estimates of species abundance are of key importance in population and ecosystem level research but can be hard to obtain. Study designs using camera traps are increasingly being used for large-scale monitoring of species that are elusive and/or occur naturally at low densities. Golden eagle (Aquila chrysaetos) is one such species, and we investigate whether existing large-scale monitoring programs using baited camera traps can be used to estimate the abundance of golden eagles, as an alternative to traditional labour-intensive searches for active territories and nest sites during the breeding period.3. The camera-trap data allowed two measures of abundance to be estimated within each of four main study areas in mid and northern Norway; occupancy was measured as the probability of camera site use, and population size was measured as the number of individuals using camera sites within a study area. Spatial and temporal patterns in occupancy and population size were explored and evaluated against independent estimates of breeding pair density in the study areas.4. Annual estimates of golden eagle occupancy showed low precision, while estimates of population size were more precise in relation to both estimated and anticipated abundance fluctuations. Estimates of population size may therefore be suitable for monitoring within-study area temporal abundance trends, while estimates of occupancy seem unsuitable for such for golden eagles. Across study areas, patterns in both average occupancy and average population density estimated from population size were consistent with the spatial pattern in average breeding pair densities (r = 0.99, and r = 0.89, respectively). This suggests that camera-trap-based estimates of occupancy and population density, both reflect territory density at large spatial scales. In conclusion, our results suggest that baited camera traps can be a cost-effective strategy for monitoring the abundance of golden eagles.

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Monitoring methods for the Golden EagleAquila chrysaetosin Norway

Cited by 6 publications

References 16 publications

Age of First Territory Settlement of Golden Eagles Aquila chrysaetos in a Variable Competitive Landscape

Age of First Territory Settlement of Golden Eagles Aquila chrysaetos in a Variable Competitive Landscape

Use of two distant nesting areas as a breeding strategy of Golden Eagles (Aquila chrysaetos) in Valdres, southeast Norway

Estimating abundance in unmarked populations of Golden Eagle (Aquila chrysaetos)

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