Nine months in the Simpson Desert: The anatomy of a letter-winged kite breeding irruption

Abstract

Highly mobile animals in the world's drylands can have distinct core and irruptive ranges with the latter being occupied only during population outbreaks driven by resource pulses. Breeding events occur within the irruptive range during these periods of high resource availability. Here we quantify such an event involving the letter-winged kite (Elanus scriptus) in the Simpson Desert, Australia; a region that experiences major rainfall-driven pulses in primary productivity. The irruption of kites lasted for a minimum of nine months (12 July 2016 to 24 May 2017). Breeding was confined to July–October 2016. Population size rose from an initial count of 22 adults in July to a peak of 38 adults and 19 juveniles in October 2016. The pattern of aggregation during 2016 consisted of dispersed breeding individuals whereas by 2017 this pattern was replaced by larger non-breeding aggregations. Kites arrived in the area when small mammal abundance was relatively low, but was increasing, and bred as the abundance of small mammals reached its peak. Unexpectedly, kites departed the area when abundance of small mammals was still high and sufficient to support an additional breeding event in winter-spring 2017. Our study provides insights in to the duration and size of breeding events in the irruptive range of nomadic birds. From a management perspective it identifies the importance of the keystone tree species, Acacia peuce, as a nesting site.