Bahadori Khosroshahi et al. • MODELING PRESENCE OF NUTHATCHES 
745 
the data sets well. The Deviance and Pearson tests 
had large P-values, indicating there is a good fit of 
the data in the models. 
Model Validation .—Thirty new random sites 
were sampled in the study area to validate the best 
model. Predicted and observed outcomes were not 
fitted at one of the sampled points (Table 4). Chi- 
square results of the compared predicted and 
observed frequency of nuthatches presence/ab¬ 
sence revealed a significant value (x 2 = 96.76; 
P < 0.001), indicating good prediction power of 
the models. 
DISCUSSION 
Wildlife distribution and abundance patterns 
depend upon many environmental factors. Our 
study was a simplification of the process of 
habitat selection and identifying the most impor¬ 
tant factors in habitat use by nuthatches. We 
found sufficient evidence of a relationship be¬ 
tween presence of species and environmental 
variables. A general pattern explaining the 
relationship between habitat and species distribu¬ 
tion was derived from the final Gl.Ms developed 
for the study area. The developed model in our 
study successfully predicted the probability of the 
presence of European Nuthatches. Our study 
dearly showed that specific vegetation structure 
was the most important determinant for this 
species. Eurasian Nuthatches were present and 
nested in some of the largest (in diameter and 
height) trees in the Kheyrud Forest. Large trees 
are more likely to provide adequate and suitable 
holes, which are likely to be absent or too small in 
small trees (Bellamy et al. 1998). This agrees with 
previous studies conducted in areas with similar 
vegetation structure (Bardin 1987. Matthvsen 
1987, Clark 1991, Bellamy et al. 1998. Burkhardt 
et al. 1998. Pagenkopf and Wesolowski 2002. 
Gonza'lez-Varo et al. 2008) and significant 
predictors for Eurasian Nuthatch presence. Spe¬ 
cies presence in our study area was affected by a 
variety of tree species, but most were Oriental 
beach ( Fa gas orientalis), chestnut-leaved oak 
(Quercus castaneifolia ), and European hornbeam 
(Carp inns bet ulus) trees which usually have larger 
diameter and height. Species presence is more 
likely in areas where beach, hornbeam, and maple 
are abundant based on the third axis of CA 
analysis in the fourth model. Deciduous woodland 
'vith a high proportion of oak and beach trees is 
reported (Nilsson 1976, Matthysen 1990) to be a 
TABLE 4. Chi-square test for 30 new random sites to 
compare predicted and observed frequency of occurrence of 
European Nuthatches. 
Predicted 
Observed 
Presence Absence 
Suitable 
19 1 
20 
Unsuitable 
0 10 
10 
18 12 
more suitable environment for raising and feeding 
nuthatch offspring. 
The major plant community in the Kheyrud 
Forest within the 80-300 m asl range is Querco- 
Buxetum, which supports a variety of bird species. 
Carpino-Fagetuni gradually changed to Fagetum 
type from 700-1,000 to 1.000-1,500 m asl (Marvi 
Mohajer 2005). The elevation category of 700- 
l.(KK) m was dominated by the Fagetum plant 
community. However, because of harvest of 
beach trees, they were replaced by hornbeam. 
These two elevation bands are adjacent to each 
other and supported the same group of avifauna. 
Elevation from 300 to 700 m is dominated by 
Querco-Carpinetum. The community in this area 
was Querco in the past and. due to the harvest of 
Querco trees, they have been replaced by 
hornbeam (Marvi Mohajer 2005). The prominent 
communities in upland are Fagetum and Querco- 
Carpinetum. which have characteristics of higher 
altitude vegetation, allowing a special group of 
birds to occur in this region. Comparison of 
individual areas with the criteria for habitat 
quality strongly indicated the study area included 
suitable habitat for nuthatches in most areas of the 
forest. Overall, 80% of the entire study area was 
estimated to be suitable for nuthatches, and the 
remaining area was unsuitable, because the forest 
has been destroyed by human activities. Also, due 
to steep slopes (>70%), inappropriate plant 
species (in terms of size and structure) caused 
unsuitable habitats. Forest understory (0-10 m) 
increases in these areas, which is shown in the 
second model where the S3 variable (Stand level 
0-10 m in height) has a negative coefficient, 
indicating a negative correlation with presence of 
nuthatches. We observed this effect in the down 
slope parts of the Kheyrud Forest (from 700 m to 
lower altitudes) that have been destroyed and have 
low tree cover (a high percentage of absent points 
were recorded in this region: Fig. 1). Overall. 
Fagus orientalis, Quercus macranthera, and 
