358
German L6pez-Iborra and Jose A. Gil-Delgado
Telleria and Garza (1983). However, Zamora and Camacho (1984a) found
greater values (100 birds 10 ha- 1 ) in a holm oak forest of just 28 ha, but this
was probably due to the presence of birds foraging in habitats surrounding
the forest.
The pattern of seasonal variation of species richness (S) was similar in
both plots (r = 0.51, df = 22, P < 0.02), reaching maximum values in summer
and minima in winter (Fig. 25.1B). Species richness tended to be higher in
plot 1 than in plot 2, although the difference was less marked in springsummer (April to September: paired samples t-tests, t = 2.38, df = 12,
P < 0.05) than in autumn-winter (October to March: t = 7.78, df = 10,
P < 0.001). The values of S for both plots pooled were very similar to their
values for plot 1 alone, showing that very few species were detected in plot 2
that were lacking in plot 1. The greatest differences between total Sand S for
plot 1 occurred in late spring and summer when some irregular species in
our study area (such as Hoopoe, Cuckoo, Green Woodpecker and Night jar)
were detected only in plot 2.
Lopez (1992) compared the number of bird species expected in 10 ha for
several types of forests in the breeding season. Bird species richness in the
Avic catchment (Fig. 25.1B) lies in the middle of the range found for Iberian
holm oak forests (12-17 species 10 ha- 1 ) and close to the average for this
kind of forest (14.8 species 10 ha-I, SD = 1.7, n = 6). Holm oak forests are less
diverse than Iberian deciduous oak forests (22 species 10 ha-I, SD = 6.2,
n = 4) and mixed forests (26 species 10 ha- 1 , SD = 7.8, n = 3), but present
similar values to pine forests (12.4 species 10 ha- 1 , SD = 4.3, n = 17).
25.4 Phenological Status of Birds
Owing to their capacity to fly over long distances, birds are potentially able to
exploit resources appearing in a wide geographical range. Thus, most bird
communities include species that exploit local resources throughout the year
and species that just use seasonal bursts of food, whether in spring-summer
or in winter in mild climates. The relative importance of both kinds of species conditions the dynamics of any bird community. To study this aspect, the
species detected in the census plots have been classified (Table 25.1) into
three categories: "constant species", including resident species present in the
plots at least 50% of the study months; "summer species", including summer
migrants present in the plots regularly in the breeding seasons of both years;
and "irregular species", including all the rest of the species.
Figure 25.2 shows the seasonal variation of the percentage of individuals
included in the above phenological categories. The community is dominated
in both plots by constant species, since on average 91.6% of birds present in
plot 1 and 89.2% of birds present in plot 2 belong to this group. The average
percentage of the community included in the summer species group during
German L6pez-Iborra and Jose A. Gil-Delgado
Telleria and Garza (1983). However, Zamora and Camacho (1984a) found
greater values (100 birds 10 ha- 1 ) in a holm oak forest of just 28 ha, but this
was probably due to the presence of birds foraging in habitats surrounding
the forest.
The pattern of seasonal variation of species richness (S) was similar in
both plots (r = 0.51, df = 22, P < 0.02), reaching maximum values in summer
and minima in winter (Fig. 25.1B). Species richness tended to be higher in
plot 1 than in plot 2, although the difference was less marked in springsummer (April to September: paired samples t-tests, t = 2.38, df = 12,
P < 0.05) than in autumn-winter (October to March: t = 7.78, df = 10,
P < 0.001). The values of S for both plots pooled were very similar to their
values for plot 1 alone, showing that very few species were detected in plot 2
that were lacking in plot 1. The greatest differences between total Sand S for
plot 1 occurred in late spring and summer when some irregular species in
our study area (such as Hoopoe, Cuckoo, Green Woodpecker and Night jar)
were detected only in plot 2.
Lopez (1992) compared the number of bird species expected in 10 ha for
several types of forests in the breeding season. Bird species richness in the
Avic catchment (Fig. 25.1B) lies in the middle of the range found for Iberian
holm oak forests (12-17 species 10 ha- 1 ) and close to the average for this
kind of forest (14.8 species 10 ha-I, SD = 1.7, n = 6). Holm oak forests are less
diverse than Iberian deciduous oak forests (22 species 10 ha-I, SD = 6.2,
n = 4) and mixed forests (26 species 10 ha- 1 , SD = 7.8, n = 3), but present
similar values to pine forests (12.4 species 10 ha- 1 , SD = 4.3, n = 17).
25.4 Phenological Status of Birds
Owing to their capacity to fly over long distances, birds are potentially able to
exploit resources appearing in a wide geographical range. Thus, most bird
communities include species that exploit local resources throughout the year
and species that just use seasonal bursts of food, whether in spring-summer
or in winter in mild climates. The relative importance of both kinds of species conditions the dynamics of any bird community. To study this aspect, the
species detected in the census plots have been classified (Table 25.1) into
three categories: "constant species", including resident species present in the
plots at least 50% of the study months; "summer species", including summer
migrants present in the plots regularly in the breeding seasons of both years;
and "irregular species", including all the rest of the species.
Figure 25.2 shows the seasonal variation of the percentage of individuals
included in the above phenological categories. The community is dominated
in both plots by constant species, since on average 91.6% of birds present in
plot 1 and 89.2% of birds present in plot 2 belong to this group. The average
percentage of the community included in the summer species group during