The Canarian subspecies of Egyptian vulture (Neophron percnopterus majorensis) is currently constrained to the Eastern part of the archipelago. 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 minimize 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. This has resulted in 85% of the population being individually marked (> 400 individuals over the last 20 years). 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 used to study health parameters and to 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.
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. The impact of toxic compounds as lead from ammunition and veterinary drugs also plays a relevant role, although fortunately, poisoning events have become rare nowadays.
Annual reproductive output is generally low, with on average only 40% of pairs producing fledglings. Reproductive output varies considerably between pairs and among years. The most productive breeding season (since the start of the monitoring work) was 2016, when 60% of pairs raised at least one young. In this specific year, there was unusual heavy rainfall very early in the breeding season in February. This may improved the overall food conditions on the island, inducing many animals to reproduce, including feral goats. However, the previous record season in 2014 (30 fledglings out of 55 territories), was one of the driest years in decades. Both these extreme weather condition may result in a higher availability of food for the vultures (for instance, many animals were dying due to the drought in 2014), but we know too little about the breeding ecology of Egyptian vultures to fully understand these yearly fluctuations in reproductive output.
With 46 individuals being tagged with GPS-loggers (26 with UvA-Bird Tracking System (UvA-BiTS) and 20 with E-obs tags), we currently have an almost continuous data-flow on the spatial behaviour of more than 15% of the birds on Fuerteventura. This allows us to determine the use of space both by territorial individuals and birds in the pre-adult stage and answer specific questions about their feeding ecology, specifically, the use of predictable feeding stations, semi-predictable carcasses at farms, and natural available resources. This information is also crucial for understanding factors determining reproductive processes and settlement patterns.
Why studying movement ecology?
Canarian Egyptian vulture are just bouncing back from the brink of extinction. Although their numbers are steadily increasing, their situation still needs to be treated with particular caution. The islands are subject to rapid environmental changes, including farm intensification, tourist development, and the apparition of new infrastructures like wind farms. To ensure a future for Canarian Egyptian vultures, continuous monitoring of the species is still needed, not only to increase our knowledge of the species, but also to further fine-tune conservation efforts in response to current and future changes.
We use two different GPS systems to track our birds. Both devices have a solar powered GPS tag with rechargeable batteries and multiple on-board sensors, including a tri-axial accelerometer. Apart from geographical coordinates, these devices provide us with information on the altitude, speed and tridimensional movements according to a time interval chosen (in our case 2-5 minutes during daytime). Both devices are data-loggers, which means the collected information is first stored on the devices. Both systems differ, however, in the way data is retrieved from the loggers.
UvaA-Bird tracking System (UvaBits)
UvaBiTS devices use Bluetooth signal for data-transfer and downloading of data requires a base-station consisting of an antenna and a laptop with necessary software. Data is downloaded automatically when birds are in the reception area of the base-station. Using a relay (‘signal repeater’) this area can cover a distance of up to 14km (distance between the repeater and the main antenna) in perfect landscape and weather conditions. The device can be programmed remotely, allowing new measurement settings to be uploaded. The diverse measurement scheme features make it possible for the user to create a scheme that takes high resolution measurements at certain times, locations, or under other special conditions and lower resolution measurements at other times. For further details see http://www.uva-bits.nl/system/
E-obs devices use the GSM-GPRS signal, which is the same as mobile phones use. Hence, this system doesn’t require the use of a base-station, which facilitates the downloading of data, which is particularly convenient for those birds living in remote areas of the island and/or do not visit the feeding stations very often. Devices are also equipped with a high-speed radio-link for wireless on-site data download, in case of absence of mobile phone towers. All information collected by the e-obs devices is being sent on a daily basis at a specific time. If a device does not connect for any reason, data are kept until a new connection is made. In addition, we can localize any target individual using radiotracking. For further details see www.e-obs.de