Luis Cadahía

Accuracy of Lightweight Satellite Telemetry: a Case Study in the Iberian Peninsula

Abstract Here we provide the first assessment of the accuracy of lightweight satellite transmitters (<80 g) under actual operating conditions and the performance of the Argos system in southern Europe. To estimate transmitter accuracy we used transmitters equipped with a Global Positioning System (GPS) and compared the location estimates provided by Argos with the estimates provided by the GPS. Using the 68th percentile to define the accuracy of locations estimates, observed accuracy was 4 km for Location Class (LC) 1, 15 km for LC 0, 20 km for LC A, and 59 km for LC B, which is in line with estimates reported by other authors. Yet, the error of the remaining 32% of the data ranged between 4 km and 11 km, 15 km and 217 km, 20 km and 145 km, and 59 km and 493 km, respectively, suggesting that using the 68th percentile to estimate accuracies might give misleading confidence on the accuracy of location estimates. Using the 90th percentile is probably more appropriate. Less than 10% of the locations we obtained corresponded to the more accurate LCs (3, 2, and 1), with Argos failing to provide a position estimate in 45% of the attempts. The low number of high-quality location estimates is likely a consequence of the electromagnetic interference reported for our study area, rather than a defect of the Platform Transmitter Terminals (PTTs), which under good conditions of signal reception seem to be as reliable as heavier ones. The recent advent of lightweight GPS transmitters overrides most of these problems. Yet, whereas the smallest Argos-GPS PTTs weigh 30 g, which restricts their use to animals weighting >1,000 g, conventional PTTs can be as small as 9.5 g, allowing their use with animals weighting 250–300 g.

Satellite telemetry reveals individual variation in juvenile Bonelli’s eagle dispersal areas

Natal dispersal is the time elapsed between departing from the natal site and settling to attempt breeding for the first time. In long-lived species with deferred sexual maturity this period may last several years, making this process crucial for their survival and conservation. Here we present a large-scale outline of juvenile Bonelli’s eagle’s dispersal areas in the Iberian Peninsula. We describe the ranging and movement patterns of 14 juvenile Bonelli’s eagles during their dispersal period, studied by satellite telemetry. Three distinct phases during the juveniles’ first year of life were detected, namely, the dependence period, the departure from the parental territory, and the settlement in dispersal areas. In general, between-sex differences in relation to ranging behavior were not significant. Interestingly, there seems not to be a few, clearly delimited, overlapping Bonelli’s eagle’s juvenile dispersal areas within the Iberian Peninsula. A total of 17 dispersal areas were detected, with some animals using more than one. These areas were located in eight autonomous communities (Spanish administrative units), being the most important Castilla-La Mancha and Andalucía. Juveniles were more frequently located in cultivated man-managed areas, with non-irrigated herbaceous crops. This is probably due to higher prey availability and higher efficiency in prey capture in these open areas, as well as to the absence of breeding pairs. This has important management implications, suggesting that conservation efforts should focus on the whole landscape matrix of man-managed ecosystems rather than in a few clearly delimited geographic areas.

MHC class I genes of birds of prey: isolation, polymorphism and diversifying selection

The threat of emerging infectious diseases encourages the investigation of functional loci related to host resilience, such as those belonging to the major histocompatibility complex (MHC). Through careful primer design targeting to conserved regions of MHC class I sequences in birds, we successfully amplified a genomic fragment spanning exons 2–4 in three birds of prey. The identification of a highly conserved region within intron 2 allowed cross-amplifying complete exon 3 sequences in diurnal raptors, owls and New World vultures. We found evidence through PCR and cloning for 1–2 polymorphic class I loci, although this is almost certainly an underestimate. Inferences of diversifying selection in the kestrel MHC revealed that the two major regions of exon 3 exhibiting positive selection mostly agree with those described for the human HLA-A2 molecule. In contrast to passerines, where a high incidence of gene duplications and pseudogenes has been commonly documented, birds of prey emerge as nice model species for the investigation of the evolutionary significance and conservation implications of MHC diversity in vertebrates.

Low mitochondrial DNA diversity in the endangered Bonelli’s Eagle (Hieraaetus fasciatus) from SW Europe (Iberia) and NW Africa

This study is an initial survey of the genetic diversity and population structure of the endangered Bonelli’s Eagle (Hieraaetus fasciatus) in SW Europe (Iberia) and NW Africa, two locations where the species has undergone a severe decrease in numbers during the last decades. It is also the first study in which the mitochondrial control region (CR) has been used to study the genetic diversity and population structure of this species. Samples were obtained from 72 individuals from Spain, Portugal and Morocco, and a 253-bp fragment of the mitochondrial control region was amplified and sequenced. Only three polymorphisms were present, indicating low nucleotide and haplotype diversity. No evidence of genetic structure was found. Several hypotheses may explain these results, including a possible greater genetic diversity in other regions of the mitochondrial genome or the existence of a presumed ancient bottleneck (last glaciation), possibly followed by a human-induced more recent one (twentieth century).

Are important bird areas and special protected areas enough for conservation?: the case of Bonelli’s eagle in a Mediterranean area

The Bonelli’s eagle (BE) is considered by the European Union as a high-priority species for conservation in the Valencian Community (East of Spain). However, in 2006 the European Union opened a legal procedure against the Spanish Kingdom, accused of lacking of an adequate network of special protected areas (SPAs) to preserve the BE in the region. Here we evaluate whether important bird areas (IBAs) and SPAs network is enough to preserve this species, on the basis of a thorough analysis of habitat preferences. A GAP analysis is performed to conduct a revision of current SPAs and BirdLife proposed IBAs. Our results suggest that the current network of SPAs becomes insufficient to protect the BE. The IBAs network, although improves the current network of SPAs, increasing the percentage of BE potential habitat included, also results inadequate. We propose a new SPAs network according to the potential suitable habitat for the species. Given the trade-off between financial investment and the conservation of biodiversity, we propose to maximize the surface of potential habitat included in the protected network minimizing the surface of the region that would be necessary to protect, thus avoiding an unnecessary expense and otherwise unrealistic results.

Bonelli's Eagle Hieraaetus fasciatus juvenile dispersal: hourly and daily movements tracked by GPS

Capsule Birds cover daily distances not normally exceeding 20 km during the initial phase of dispersal, with the daily peak of movement/activity in the afternoon.

Natal dispersal and recruitment of two Bonelli's Eagles Aquila fasciata: a four-year satellite tracking study

Abstract. To study natal dispersal and recruitment to the breeding population in Bonellis Eagle, two nestlings were tagged with satellite transmitters in the Iberian Peninsula in 2002. Their monthly ranges and distances were computed and fitted to regression models to describe their general trend. One bird, a female, dispersed and settled rapidly in an area which she explored intensively during four years and which finally became her first breeding site. The natal dispersal distance was 441 km, and the bird cannot therefore be considered philopatric. The other bird, a male, alternated between long travelling episodes and settlement in particular areas, exploring different regions both distant from and close to his natal territory, but no breeding attempt could be confirmed after four years of tracking. The large distances we recorded confirm the potential for gene flow among populations but, in comparison with our results from previous studies, they suggest that Bonellis Eagles may show high variation in their natal dispersal distances and use different dispersal strategies.

The first case of successful breeding of a Golden Eagle Aquila chrysaetos tracked from birth by satellite telemetry

Abstract. The natal dispersal of a Golden Eagle from its natal eyrie to the site where it reproduced for the first time was monitored. After covering > 16 000 km2 in its three years of juvenile dispersal, and despite flying > 130 km from its natal site, the eagle finally settled in a vacant territory just 26 km away from the place where it had hatched. Almost 95% of the total dispersal area was visited for the first time during the first year of tracking; less than 40% of the dispersal area was used during the remainder of the dispersal period. During dispersal the eagle regularly visited territories occupied by adult Golden Eagles. Previous records of the occupancy of the territory the eagle currently occupies show an alternation between periods when it remained vacant with periods when subadults occupied it. Although the other member of the breeding pair is also a subadult eagle, the birds managed to raise two fledglings.

Noninvasive Estimation of Minimum Population Sizes and Variability of the Major Histocompatibility Complex in the Andean Condor

Abstract. Estimating indices of abundance of threatened species is crucial to preserving biodiversity. Over the last few decades, noninvasive genetic sampling has proven to be a more straightforward and less expensive approach than capture—mark—recapture analyses. In particular, molted feathers have become extremely popular for the monitoring of bird populations. Diagnostic molecular markers such as microsatellites, however, are still not available for many avian species of conservation concern. Highly polymorphic genes of the major histocompatibility complex (MHC), on the other hand, have become reasonably accessible during the last few years. We tested the suitability of MHC profiles as DNA fingerprints to assist the identification of individuals of a scavenger difficult to monitor through traditional approaches, the Andean Condor (Vultur gryphus). To achieve this aim, we isolated polymorphic and putatively functional genes of MHC class I (exon 3, 6 alleles) and MHC class IIB (exon 2, 11 alleles). Single-strand conformational polymorphism and direct sequencing of MHC genes, combined with molecular sexing and inference of age class from feather color, allowed us to identify 80 different individuals from 110 molted feathers collected at roost sites. Inferred sex and age ratios were concordant with previous studies relying on direct observations. Among adults, the number of males was double that of females; among juveniles, this ratio was inverted. Besides providing valuable data regarding genetic variation at functionally important genes related to resistance to pathogens, we demonstrate additional potential of polymorphic MHC loci beyond their well-known role in evolutionary ecology.

Markov models of territory occupancy: implications for the management and conservation of competing species.

Markov chains have been frequently used in community ecology to model successional changes, but little attention has been paid to its application in population ecology as a tool to explore the outcomes of species interactions. Markov models can be regarded as “null models” that provide predicted values under a no-change scenario against which the consequences of changes in variables of interest can be assessed. Here we explore Markov chains’ potential to project population trends of competing species and derive sensible management strategies. To do that we use six years of field data on territory occupancy and turn-over of two competing top predators in a Mediterranean landscape: the golden and Bonelli’s eagles. The results suggest that long-term coexistence of both species in the study area is likely, with the main limitation for their coexistence being the difficulties Bonelli’s eagles have in colonising new territories that become available. To avoid future declines in the population of Bonelli’s eagle, it is important to take into account that the positive effects of conservation strategies focused on encouraging colonization (e.g. decreasing disperser mortality) are likely to be larger than those focused on avoiding territory abandonment (e.g. decreasing adult mortality). Markov chains are likely to be useful to evaluate the relative merit of alternative management options in other territorial species when patterns of territory occupancy are the only reliable data available, as often happens with large predators.