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Authors: Stefano Scali, Oscar Donelli, Fabrizia De Leo & Ileana Negri

Introduction

A study on the habitat selection in a snake guild was conducted in a natural reserve of the Parco Lombardo della Valle del Ticino, called “La Fagiana”. The research was carried out from 1996 to 2005 and all the data were gathered to investigate the habitat features affecting snake distribution in the study area.


The snakes were searched, captured and individually marked along a nearby standard path about 16 km long. Five species were found in the area (ntot=563): Natrix natrix (n=252), N. tessellata (n=58), Hierophis viridiflavus (n=170), Zamenis longissimus (n=72), and Vipera aspis (n=12). The real study area was defined as the standard path plus a buffer 150m wide. A 100m square grid (no. of cells=281) was overlapped to the area map and the habitat of each cell was characterised as follows, using a GIS software: surface covered by each vegetation type, ecotone and stream length. Habitat preferences were analysed with a logistic regression, using the presence of snakes as the dependent variable and habitat descriptors as the covariates.

The forward stepwise likelihood ratio logistic regression analyses were significant for all the species; the results, including extracted variables and coefficients, are reported in the following table.
 

Species Variable B SE

Change in –2LL
if term is removed

DF P EXP (B)
N. natrix Ecotones

0.003

0.001

14.081

1

0.001

1.003

N. tessellata

Mature wood

0.0002

7.45E-05

6.486

1

0.01

1.000

  Ecotones

0.003

0.001

3.988 1

0.05

1.003

H. viridiflavus Mature wood

0.0002

5.40E-05

18.261

1

0.001

1.000

 

Scrub

0.0001

6.36E-05

4.616 1

0.05

1.000

  Stream

-0.014

0.005

8.729

1

0.01

0.986

  Ecotones

0.003

0.001

8.686 1

0.01

1.003

Z. longissimus Mature wood

0.0001

5.24E-05

5.481

1

0.05

1.000

V. aspis Stream

-0.022

0.013

5.517 1 0.019 0.978

The classification was correct in 80.4% of cases for N. natrix, in 95.0% of cases for N. tessellata, in 86.5% for H. viridiflavus, in 89.0% for Z. Longissimus, and in 96.4% for V. aspis.

The results showed a clear preference of snakes for natural woods and scrub, with extended ecotones. Natrix natrix is a generalist species and it is present over the whole area; it seems not to be affected by vegetation type, but only by ecotone length. The terrestrial habitat of N. tessellata, a mainly aquatic snake, is characterized by mature deciduous woods with long ecotones. Hierophis viridiflavus prefers dry areas with a rich and varied vegetation, often fragmented by ecotones. The presence of Zamenis longissimus is mainly affected by mature deciduous woods, being a forest, tree-dweller species. V. aspis presence is not correlated to any vegetation type, and this species only seems to prefer dry and sunny areas.

In conclusion, the study confirms the importance of a well preserved and varied habitat for the maintenance of a well-structured snake guild. The presence of different habitats and of forbidden areas to tourists allow a high diversity in the snake guild and the survivorship of large populations even in an area subject to intensive recreational activities.

Courtesy of the Societas Herpetologica Italica and authors:

This site has information on the following genera of Ratsnakes ... Spilotes, Spalerosophis, Ptyas, Zamenis, Elaphe, Rhinechis, Senticolis, Pseudelaphe, Pantherophis, Bogertophis, Orthriophis, Gonyosoma, Oreocryptophis, Oocatochus, Euprepiophis, Coelognathus, Archelaphe