The effect of Aleppo pine (Pinus halepensis) invasion on nests predation

In this study, I examined how the invasion of pine trees affects the populations of the Sardinian warbler (Sylvia melanocephala) in the Mediterranean scrubland. My hypothesis was that the invasion of pine may benefit to avian predators, like the Eurasian jay (Garrulus glandarius), thus, increasing predation pressure on the Sardinian warbler. The research question was examined in four habitats that differ in pine densities of pine using two methods:

1) Placing dummy nests with eggs to identify signs of predators according to predation marks on the eggs.

2) Acoustic monitoring of mobbing calls of the Sardinian warbler and calls of the Eurasian jay.

Results

Nest predation was highest in the scrubland with scattered pine trees (75% of the nests were preyed) and open pine forest (60%). Predation pressure was lowest in the scrubland without pines (42%) and dense pine forests (32%). Acoustic analysis showed the presence of jays different among the four habitats. Their calls were most frequent in the scattered pine forest and scrubland with scattered pine trees. Furthermore, the mobbing events of the Sardinian warbler were most frequent in the open pine forest (13.6 events per 40 cycles recording) and the scrubland with scattered pine trees; the lowest was in the scrubland (an average of 4.5 events).