On habitat-specific nutritional condition in graceful warblers Prinia gracilis: Evidence from ptilochronology

Dry salt marshes of the Rift Valley in Israel are subject 1to development. This is of special concern because the peace process has led to a boom of financial investment and a flood of ideas as to how these areas can be further exploited. This includes Eilat, an important migratory bottleneck on the northern edge of the Saharan-Arabian desert belt, which is critical for many avian migrant species because in spring it is reached after a flight of almost 2000 km across continues deserts. Of the once extensive Eilat salt marsh of 12 km², all that remains today is a piece of only 0.04 km². An avian study of this habitat concluded that the salt marsh was important for the survival of at least 70 species of migrant passerines that staged in the salt marsh. In order to evaluate the optimality of the salt marsh and reed beds for the birds I sampled a resident species as a bioindicator. I hypothesized that ptilochronology would allow me to compare between the habitats and to rank their relative importance to avian populations. During autumn 1993 and spring 1994, 59 Graceful Warblers from territories in the reeds, and 41 from the salt marsh were trapped and a central rectrix plucked for analysis. The average of 10 growth bars of the rectrix of the birds from the reeds were significantly broader than those of the salt marsh. A comparison of the two habitats clearly shows that the reed beds are a superior resource to the birds than the existing salt marsh.