Hunting Altitude of Eleonora's Falcon (Falco eleonorae) Over a Breeding Colony

Abstract

We investigated the flight altitude of hunting Eleonora's Falcons (Falco eleonorae) around their colony near the island of Crete (Greece). We used a broadband marine surveillance radar positioned on the coast of Crete and detected the falcons’ movements during the breeding period. The birds were monitored using a Java application that enabled us to manually track radar targets directly on the radar screen and transfer the data into a GIS environment. Thirty hours of radar monitoring between 14 September and 22 September 2017 produced 4774 records of the species (1218 over inland and 3556 over the sea). Hunting falcons flew on average at 1292 ± 11 masl (range = 17–3475, median flight altitude 1156 m), though 70% of them were tracked flying between 17 and 1750 m. The range of flight altitude recorded was greater than that previously published, and was consistent with the prey selection during the nestling-rearing period, i.e., migratory passerines. Eleonora's Falcons hunted more frequently over the sea than over the mainland and at a higher altitudes during the morning than at midday or in the afternoon. The daily flight pattern probably reflected the higher intensity of passerine migration in the early morning and late afternoon, as well as an opportunistic prey shift from birds to insects during midday when passerine migration is weak. Compared to other techniques previously used for tracking this species, namely visual observations (1970s), optical range finder (1990s), and satellite telemetry (2000s), broadband marine radar is not limited by small sample size, geolocation error, weather conditions, or poor visibility at high altitudes.