Out of Africa: Juvenile Dispersal of Black-Shouldered Kites in the Emerging European Population

Abstract

Knowledge of animal dispersal patterns is of great importance for the conservation and maintenance of natural populations. We here analyze juvenile dispersal of the poorly studied Black-shouldered Kite (Elanus caeruleus) monitored in southwestern Spain in an ongoing long-term study initiated in 2003. The European population of Black-shouldered kites is thought to be a recent one funded by colonizing African birds, as no kites have been found in the European fossil record, and the breeding population has progressively expanded to the North in the late 20th and 21st centuries. We obtained information on movements behavior during dispersal from 47 juveniles Kites after marking 384 nestlings with wing tags and three nestlings with radio transmitter. We have tested two competing hypotheses (i.e., the Resources Competition Hypothesis and the Wandering Hypothesis (WH)) that may explain the leptokurtic distribution of the natal dispersal distance in Elanus. After independence, juvenile females dispersed farther from the natal areas than males, as is common in birds. On average, males and females dispersed from their natal areas over 9 (i.e., 26.15 km) and 15 (i.e., 43.79 km) breeding territories, respectively. A male and two females dispersed further than 100 km from their natal nest. Our results indicated some evidence supporting the competition-for-resources hypotheses since nestlings hatched from high quality territories stayed closer from natal areas than nestlings hatched from low quality territories and also nestlings hatched first within the brood also tend to recruit closer to their natal area than later hatched nestlings which tend to disperse further away from their natal area. The information provided by these crucial demographic parameters will be used for the elaboration of future conservation plans for the management of this colonizing species in Europe.

Keywords: brood rank order; laying date; natal dispersal; range expansion; resource competition hypothesis; wandering hypothesis.

Figure 1

The photographs depicted (a) a brood of three nestlings with two of them wearing wing tags on the right wing; (b) a nestling equipped with an emisor.

Figure 2

The top panels depicted the juvenile dispersal distance (km) of male (A) and female (B) Black-shouldered Kite (Elanus caeruleus) studied in southwestern Spain. The bottom panels depicted the juvenile dispersal distance (km) of male (C) and female (D) after excluding one male and two females that dispersed further than 100 km from their natal site.

Figure 3

Boxplot for juvenile dispersal distance (km) of male and female Black-shouldered Kites (Elanus caeruleus) monitored in southwestern Spain. Horizontal lines = median and boxes are inter-quartile range. Sample size is 30 males and 17 females.

Figure 4

Partial residual plot of natal dispersal distance (km) in relation to territory occupation rate of Black-shouldered Kites (Elanus caeruleus) studied in southwestern Spain. The line is the prediction of territory occupation rate on natal dispersal distance while maintaining the other predictor in the model on their mean values. 95% CI are shaded in grey color.

Figure 5

Boxplot for natal dispersal distance (km) according to brood rank order of Black-shouldered Kites (Elanus caeruleus) monitored in southwestern Spain. Horizontal lines = median and boxes are inter-quartile range. Sample size is nine, six and six first, second and third-order hatched nestlings within the brood, respectively.