DO BROWN PELICANS MISTAKE ASPHALT ROADS FOR WATER IN DESERTS?

• Published in: Acta zoologica Academiae Scientiarum Hungaricae (Budapest, Hungary : 1994) Vol. 54; pp. 157 - 165
• Main Authors: Kriska, G, Barta, A, Suhai, B, Bernath, B, Horvath, G
• Format: Journal Article
• Language: English
• Published: 01.01.2008
• Subjects: Marine; Pelecanus occidentalis; USA, Arizona
• ISSN: 1217-8837

Recently, brown pelicans (Pelecanus occidentalis) have been observed to crash on roads in Arizona. It was hypothesized that the pelicans have mistaken the heat-induced shimmer of the asphalt surface for lakes. Here we propose two counter-arguments for this proposition: (i) The edge of a mirage can never be reached, because it continuously moves away when the observer tries to approach it. (ii) We show by computation that the edge of the mirage from a landing brown pelican is so distant that the bird cannot reach it by gliding, even if the edge did not move off, independently of the beginning height of gliding. Consequently, the brown pelicans should have known at the moment of decision for landing that they could not reach the distant shimmering part of the asphalt road by gliding, and thus they would be forced to land on the asphalt. If the dry asphalt surface is smooth enough, the reflection of sunlight from the asphalt could deceive water-seeking flying pelicans, which is explained in detail here. Another explanation could be that brown pelicans may not be "intelligent" enough to grasp that they can never reach the continuously moving off shiny distant part of an asphalt road.