Migratory animals are affected by various factors during their journeys, and the study of animal ... more Migratory animals are affected by various factors during their journeys, and the study of animal movement by radars has been instrumental in revealing key influences of the environment on flying migrants. Radars enable the simultaneous tracking of many individuals of almost all sizes within the radar range during day and night, and under low visibility conditions. We review how atmospheric conditions, geographic features and human development affect the behavior of migrating insects and birds as recorded by radars. We focus on flight initiation and termination, as well as in‐flight behavior that includes changes in animal flight direction, speed and altitude. We have identified several similarities and differences in the behavioral responses of aerial migrants including an overlooked similarity in the use of thermal updrafts by very small (e.g. aphids) and very large (e.g. vultures) migrants. We propose that many aerial migrants modulate their migratory flights in relation to the in...
This is a review about the use of salines and fishponds by breeding and wintering waders. The sal... more This is a review about the use of salines and fishponds by breeding and wintering waders. The salines are the habitat select by most of breeding waders. In winter these habitats are use as foraging alternative areas according to their characteristics. It is also analyzed the noctunal use of these habitats, as well as their use as roosting sites.
ABSTRACT The Balearic Shearwater Puffinus mauretanicus is considered the most threatened seabird ... more ABSTRACT The Balearic Shearwater Puffinus mauretanicus is considered the most threatened seabird in Europe, based on a prediction of extinction within 3 generations in average. Such prediction was computed in 2004, based on a population estimate of 2,000 breeding pairs at that time. However, the breeding population has been recently updated to 3,193 pairs. Furthermore, figures for the global population, merely inferred from the breeding population, were thought to be within the range of 8,000-15,000 individuals at most. New estimates of the global population are presented here, from two different approaches: boat-based surveys at sea and coastal counts of migrating birds. Boat-based surveys consisted in transect counts that covered systematically the Iberian Mediterranean shelf in November-December 2003-2005, i.e. during the pre-breeding period when the bulk of the global population is present there. Bootstrap procedures were used to infer a global estimate of Balearic Shearwaters from the observed densities at sea. Coastal counts were performed from Tarifa (Strait of Gibraltar) from mid May to mid July 2007-2010, covering the peak of the post-breeding outflow to the Atlantic. Coverage varied among years from 37% to 67% of the daylight time and estimates for the whole period were inferred using GAM models. Both methodological approaches provided similar figures, which were also consistent between years, with conservative estimates of about 25,000 birds. These figures could not be easily explained with the currently estimated breeding population, according to a basic model that incorporated conceivable demographic parameters to link breeding and total populations. It is crucial to clarify the species’ population size and its demographic structure by reinforcing census and monitoring effort in the breeding grounds, as well as keeping the census efforts at sea, since they provide key information to assess the extinction time of a species while misestimating could result in ineffective conservation strategies.
SummaryThe Balearic Shearwater Puffinus mauretanicus is considered one of the most threatened sea... more SummaryThe Balearic Shearwater Puffinus mauretanicus is considered one of the most threatened seabirds in the world, with the breeding population thought to be in the range of 2,000–3,200 breeding pairs, from which global population has been inferred as 10,000 to 15,000 birds. To test whether the actual population of Balearic Shearwaters is larger than presently thought, we analysed the data from four land-based census campaigns of Balearic Shearwater post-breeding migration through the Strait of Gibraltar (mid-May to mid-July 2007–2010). The raw results of the counts, covering from 37% to 67% of the daylight time throughout the migratory period, all revealed figures in excess of 12,000 birds, and went up to almost 18,000 in two years. Generalised Additive Models were used to estimate the numbers of birds passing during the time periods in which counts were not undertaken (count gaps), and their associated error. The addition of both counted and estimated birds reveals figures of be...
Migratory animals are affected by various factors during their journeys, and the study of animal ... more Migratory animals are affected by various factors during their journeys, and the study of animal movement by radars has been instrumental in revealing key influences of the environment on flying migrants. Radars enable the simultaneous tracking of many individuals of almost all sizes within the radar range during day and night, and under low visibility conditions. We review how atmospheric conditions, geographic features and human development affect the behavior of migrating insects and birds as recorded by radars. We focus on flight initiation and termination, as well as in‐flight behavior that includes changes in animal flight direction, speed and altitude. We have identified several similarities and differences in the behavioral responses of aerial migrants including an overlooked similarity in the use of thermal updrafts by very small (e.g. aphids) and very large (e.g. vultures) migrants. We propose that many aerial migrants modulate their migratory flights in relation to the in...
This is a review about the use of salines and fishponds by breeding and wintering waders. The sal... more This is a review about the use of salines and fishponds by breeding and wintering waders. The salines are the habitat select by most of breeding waders. In winter these habitats are use as foraging alternative areas according to their characteristics. It is also analyzed the noctunal use of these habitats, as well as their use as roosting sites.
ABSTRACT The Balearic Shearwater Puffinus mauretanicus is considered the most threatened seabird ... more ABSTRACT The Balearic Shearwater Puffinus mauretanicus is considered the most threatened seabird in Europe, based on a prediction of extinction within 3 generations in average. Such prediction was computed in 2004, based on a population estimate of 2,000 breeding pairs at that time. However, the breeding population has been recently updated to 3,193 pairs. Furthermore, figures for the global population, merely inferred from the breeding population, were thought to be within the range of 8,000-15,000 individuals at most. New estimates of the global population are presented here, from two different approaches: boat-based surveys at sea and coastal counts of migrating birds. Boat-based surveys consisted in transect counts that covered systematically the Iberian Mediterranean shelf in November-December 2003-2005, i.e. during the pre-breeding period when the bulk of the global population is present there. Bootstrap procedures were used to infer a global estimate of Balearic Shearwaters from the observed densities at sea. Coastal counts were performed from Tarifa (Strait of Gibraltar) from mid May to mid July 2007-2010, covering the peak of the post-breeding outflow to the Atlantic. Coverage varied among years from 37% to 67% of the daylight time and estimates for the whole period were inferred using GAM models. Both methodological approaches provided similar figures, which were also consistent between years, with conservative estimates of about 25,000 birds. These figures could not be easily explained with the currently estimated breeding population, according to a basic model that incorporated conceivable demographic parameters to link breeding and total populations. It is crucial to clarify the species’ population size and its demographic structure by reinforcing census and monitoring effort in the breeding grounds, as well as keeping the census efforts at sea, since they provide key information to assess the extinction time of a species while misestimating could result in ineffective conservation strategies.
SummaryThe Balearic Shearwater Puffinus mauretanicus is considered one of the most threatened sea... more SummaryThe Balearic Shearwater Puffinus mauretanicus is considered one of the most threatened seabirds in the world, with the breeding population thought to be in the range of 2,000–3,200 breeding pairs, from which global population has been inferred as 10,000 to 15,000 birds. To test whether the actual population of Balearic Shearwaters is larger than presently thought, we analysed the data from four land-based census campaigns of Balearic Shearwater post-breeding migration through the Strait of Gibraltar (mid-May to mid-July 2007–2010). The raw results of the counts, covering from 37% to 67% of the daylight time throughout the migratory period, all revealed figures in excess of 12,000 birds, and went up to almost 18,000 in two years. Generalised Additive Models were used to estimate the numbers of birds passing during the time periods in which counts were not undertaken (count gaps), and their associated error. The addition of both counted and estimated birds reveals figures of be...
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Papers by Gonzalo Arroyo