Quantitative analysis of bird migration over Israel

Israel is located in the heart of one of the largest migration flyways in the world. Yet, the properties of this major migration flyway have only been rarely studied, resulting in poor understanding of this system. Using data from five consecutive years (2014-2018) collected by three weather radars and six vertical-looking bird radars that were positioned throughout Israel, we investigated the nocturnal avian migration over the country. We applied the vol2bird algorithm to quantify autumn and spring migration properties and examined the meteorological conditions that influenced key migration attributes. We found that temperature was the most influential factor affecting migration intensity in spring, and temperature difference from the previous night and wind intensity affected autumn migration. Migration flight altitude, which is influenced by the degree of wind support towards seasonal bird destination, differed between autumn and spring but only in central and southern Israel, likely reflecting the transition between the trade-wind circulation zone that is found south of latitude 30 north and the temperate circulation zone that is found north of this latitude. We found that, unlike studies in Europe and the US, spring migration intensity is only about half of the autumn migration’s intensity, with the exception of the Hula Valley where springtime bird migration intensity was substantially higher from anywhere else in the country and possibly in the world. Our updated calculations suggest that previous estimates of bird migration intensity were considerably underestimating the actual number of migrants travelling through Israel.