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

Asaf Ben David, Tamar Dayan, Ido Itzhaki

The invasion of pine (Pinus Halepensis) to the Mediterranean scrubland and natural woodland, changes the composition and height of the vegetation. These changes may alter the movement of predators and thus increase predation pressure on prey. Predation in the nesting season is one of the most significant factors influencing the size of the population of song birds.

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).

The high predation in the scrubland with the invading pines is associated with jays

A model was developed to predict the chances of a nest to be preyed. It showed that habitat with scattered pines and progress of the nesting season have a significant positive effect on the chances of a nest to be preyed. I found no significant influence of environmental variables such as the pine count, vegetation cover and vegetation height on nest predation. Although I have identified vary nests predators such as rodents and reptiles, I suggest that the high predation in the scrubland with the invading pines is associated with jays. I assume jays use vantage points in the pine trees in the areas of scrubland thus increasing predation pressure on nesting songbirds in the invading pine areas.