Population Monitoring

The Canarian subspecies of Egyptian vulture (Neophron percnopterus majorensis) is currently constrained to the Eastern part of the archipelago with a total population of 300 individuals and less than 60 breeding pairs. The population has been monitored intensively by the EBD team since 1998, when only 23 territories were occupied. Ever since, 2 or 3 persons stay on Fuerteventura permanently from late February until September. During this period of extensive fieldwork, territories and nest in both islands are localized and visited. To minimise disturbance, nests are only visited at particular stages during the breeding season to collect specific information, and by a few experienced people. In this way, data has been collected on the identity of breeding pairs and essential aspects of the vulture’s reproduction, including information on the location of nest, the presence of incubating birds and the number of fledglings. In addition, each year, fledglings are individually marked with metal and plastic rings with alphanumeric codes, allowing identification of these birds in the field and to estimate juvenile survival in subsequent years (click on pictures to enlarge).

Apart from this, two-yearly trapping sessions in baited places have taken place since 1998 to catch adult birds. A total of 289 birds (108 females and 129 males) have now been caught for scientific purposes and released, and together with the ringing of nestlings (91 females and 87 males in total), this has resulted in 85% of the population being individually marked in 2015 (415 individuals over the last 17 years). Furthermore, from all birds (nestlings and adults), biometric measurements are taken, which include information on the body-size (wing/tail-length and bill-size, tarsus-length) and body-mass. Blood-sample are taken to determine their health parameters and determine the genetic relatedness among birds.

Additional information is collected on roosting behaviour, by regular counts of number of adults and immature birds on electricity pylons throughout the island. Data on local survival is obtained by reading plastic rings of birds using telescopes, mainly from hides at the feeding stations, but whenever possible, individuals are checked on their plastic rings throughout the island.

This extensive field-work has made the Canarian Egyptian vulture population unique in the world, as no other vulture populations exist in which for the majority of individuals their complete life-history is known.


Population trends

The Canarian Egyptian vulture population is increasing about 5% per year but still supports relatively high rates of unnatural deaths, mainly caused by accidents on power lines, although the impact of toxic compounds as lead from ammunition and veterinary drugs plays also a relevant role.

mortality

Nevertheless, conservation measures so far have resulted in a doubling of the breeding population on Fuerteventura since 1998 (23 vs 55), with an overall increase of the number of individuals living on Fuerteventura and Lanzerote from 100 to 300 individuals.

Population trends

Figure 1. Increase in number of breeding pairs on Fuerteventura in the last 15 years.  The occupancy of ‘traditional’ territories (= present before 1998)  has remained relative stable over time, but many new territories have been formed since 2000.

Despite this positive population trend, the overall reproductive output is still remarkably low compared to mainland Spain (only 0.4 vs 1.1 fledglings per nest for FV and Spain respectively). Breeding success in old ‘tradional’ territories (< 1998) is low, but relatively stable (Figure 2). New breeders in particular have very low breeding success (figure 3). Average year of recruitment is about 6 years (range 4-13, n = 161, sexes pooled). Median number of breeding seasons per individual is 3 (range 1-15, n = 161, sexes pooled)

tradional_territories

Figure 2. Number of tradional territories occupied and proportion of succesful nests (at least 1 fledgling). Note the that reproductive success in old territories is relatively stable, but very low.

new_territories

Figure 3. Total number of ‘new’ territories (occupied after 1999) and proportion of successful nests (at least 1 fledgling). Note that most new territories are unsuccessful.

 

 

 

 

 

 

 

 

 

 

 

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