Impact of Grazing on Reptiles in Mediterranean Woodland in Israel

Roy Talbi, Ido Itzhaki and Avi Bar Massada

The study focuses on the effects of cattle grazing on the reptile community in Mediterranean woodlands in northern Israel, through the changes in vegetation structure and the presence of the cattle egret (Bubulcus ibis), a predator that accompanies cattle in the field. The study sheds light on the role of this overabundant species, which until now was not considered problematic for the ecosystem; it is now clear that its impact on small animals at the base of the food web is significant to the point of deterioration of such species that are usually highly abundant in woodland areas.

Cattle-Egret-foraging-from-the-back-of-a-cow-Ramat-Hanadiv-May-2017-aspect-ratio-x

Background
The consequences of modern nature conservation and the management actions derived from the dynamics of human civilisation on plant and animal ecology occupy many ecologists around the world in general and in the Mediterranean Basin in particular. The present study focuses on the reptile community as a model for the impact of management actions on the woodland, a group that has not been studied previously from this perspective in Israel or in the Mediterranean Basin. As a general rule, various land uses pose a significant threat to reptiles around the world, but knowledge about their impacts on species composition or on community responses is scarce (Thompson et al. 2016).

Cattle Egret (Bubulcus ibis) preys on a Lebanon Lizard (Phoenicolacerta laevis) in the Lower Galilee March 2017_

In recent years, researchers have recognised that reptiles can serve as successful bio-indicators for habitat quality, for a number of reasons: (1) they are common and prominent in the Mediterranean region in natural systems affected by humans; (2) observation of their activity is relatively easy and produces much information; )3) the species are relatively easy to identify and (4) studies have proven that some species are very sensitive to environmental change.

Due to the history of grazing in Israel, researchers assumed that goat grazing will benefit the reptile community, as opposed to cattle grazing, which has become common in recent decades. This management change, together with additional changes in Israel’s landscapes, has led to the establishment of the cattle egret – a predator that accompanies cattle, and was rare in the past in pasturelands, including Mediterranean woodland and forest. The assumption is that the cattle egret may pose a significant threat to the Mediterranean reptile community, particularly to the lizards.

The distribution map constructed for the cattle egret breeding colonies indicated that Ramat Hanadiv is located at the heart of the one of the most infected areas in the country’s north

Research procedure:
The sampling included a random walking route and direct observation of reptiles and dominant mammals and birds, in areas under different types of management. The sampling in Ramat Hanadiv took place over two spring seasons and two autumn seasons (2017–2018), at seven different sites around the park. Moreover, night sampling was conducted to complete data collection about the abundance of species suitable for night monitoring, such as the common chameleon (Chamaeleo chamaeleon) and Kotschy’s gecko (Mediodactylus kotschyi).

Cattle egret activity was examined by direct observation during sampling, observations from national databases and photographs from trail cameras that have operated during the last two years throughout the park. In parallel, the egrets’ diet was examined in ten colonies throughout the breeding season by analysing regurgitated food brought from the field by the adults to the chicks as well as identifying and counting individual reptiles in the egrets’ food.

Cattle Egret Nesting Colony in the Lower Galillee (Sakhnin) May 2017

Cattle Egret foraging from the back of a cow, Ramat Hanadiv April 2018

Food items regurgitated by Cattle Egret June 2018

Cattle Egret Foraging next to a cow in Lower Galillee May 2017

Results:
The distribution map constructed for the cattle egret breeding colonies indicated that Ramat Hanadiv is located at the heart of the one of the most infected areas in the country’s north, as also documented by the trail cameras and the direct observations of cattle egret flocks throughout most of the park.

The reptile community at Ramat Hanadiv is unusually poor in comparison to most woodland areas in the north. Collection and analysis of mature cattle egret regurgitations to chicks during the breeding season revealed important data on the abundance and richness of reptile species in the egrets’ diet. Analysis of the weight composition of the egrets’ food and counts of reptiles in each colony showed that reptiles comprise ca. 20% of the total diet of this species.

Cattle Egret Nesting Colony in the Lower Galillee (Sakhnin) April 2018

Conclusions:

This study reinforces the assumption that the cattle egret, as a predator, poses a threat to reptile’s populations (mainly small lizards). While grazing improves the heterogeneity of the vegetation and opens up the dense woodland – an action that is expected to benefit woodland reptiles – the presence of the cattle egret, that accompanies cattle in the field, markedly reduces the diversity of reptiles and arthropods that serve as important sources of food for reptiles and other groups of vertebrates. Therefore, it is recommended to reduce the size of the cattle herd and consider the timing and length of the grazing season. Monitoring of cattle egret activity must continue, alongside intentional harm to breeding success in their breeding colonies.

Additional links

Full scientific report (in Hebrew)

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