356
German Lopez-Iborra and Jose A. Gil-Delgado
In this chapter we describe the seasonal dynamics of the bird community
in the holm oak (Quercus ilex 1.) forest of the Prades experimental area (NE
Spain), specifically in the Avic catchment. In particular, the seasonal variations of density and diversity are analyzed, and the relative abundance of
summer migrants and the seasonal pattern of density variation are compared between several Iberian forest types.
25.2 Census Methods
We estimated the abundance of bird species using the mapping method. Although this method was originally designed to be used in the breeding season, it has been also employed to study the dynamics of bird communities
throughout the year. It was used, for instance, in the study of the role of birds
in the nutrient cycles in the Hubbard Brook Experimental Forest (Sturges
et al. 1974; Holmes and Sturges 1975).
We used two plots of 5 ha (250 x 200 m) within the Avic catchment
(Chap. 2). The area included in both plots represents 19.4% of the catchment
area. One plot (plot 1) was located at the bottom of the catchment, between
740 and 800 m a.s.l., while the other (plot 2) was located in the mid-upper
catchment, between 850 and 950 m a.s.l. In this way we may better cover the
range of variation of vegetation structure within the catchment, since holm
oaks had greater diameters and were taller at the bottom of the catchment
while their density was greater at the top. Diversity of the tree layer also varied within the catchment, being greater at the bottom (L6pez 1991).
A grid of 25 x 25 m was marked within each plot to locate the contacts
with birds. Each plot was censused in two different days in the central week
of each month. Censuses were performed in the morning and lasted for
about 2 h. The plots were walked following the lines of the grid parallel to the
longest side and the contacts and displacements of birds were registered on a
map of the plot. Singing males were counted as a pair. In order to reduce the
problem of high border-surface ratio in small plots, individuals or pairs located less than 50 m from the plot border have been counted as half an individual or half a pair since part of their home range probably lies out of the
plot. Test censuses were performed in March of 1985 in order to become familiarized with the plots, and then real censuses were performed monthly
from April 1985 to April 1987, always by the same person (G.L.I.). The data of
the two census days of each month were combined to obtain a density estimate per month in each plot.
German Lopez-Iborra and Jose A. Gil-Delgado
In this chapter we describe the seasonal dynamics of the bird community
in the holm oak (Quercus ilex 1.) forest of the Prades experimental area (NE
Spain), specifically in the Avic catchment. In particular, the seasonal variations of density and diversity are analyzed, and the relative abundance of
summer migrants and the seasonal pattern of density variation are compared between several Iberian forest types.
25.2 Census Methods
We estimated the abundance of bird species using the mapping method. Although this method was originally designed to be used in the breeding season, it has been also employed to study the dynamics of bird communities
throughout the year. It was used, for instance, in the study of the role of birds
in the nutrient cycles in the Hubbard Brook Experimental Forest (Sturges
et al. 1974; Holmes and Sturges 1975).
We used two plots of 5 ha (250 x 200 m) within the Avic catchment
(Chap. 2). The area included in both plots represents 19.4% of the catchment
area. One plot (plot 1) was located at the bottom of the catchment, between
740 and 800 m a.s.l., while the other (plot 2) was located in the mid-upper
catchment, between 850 and 950 m a.s.l. In this way we may better cover the
range of variation of vegetation structure within the catchment, since holm
oaks had greater diameters and were taller at the bottom of the catchment
while their density was greater at the top. Diversity of the tree layer also varied within the catchment, being greater at the bottom (L6pez 1991).
A grid of 25 x 25 m was marked within each plot to locate the contacts
with birds. Each plot was censused in two different days in the central week
of each month. Censuses were performed in the morning and lasted for
about 2 h. The plots were walked following the lines of the grid parallel to the
longest side and the contacts and displacements of birds were registered on a
map of the plot. Singing males were counted as a pair. In order to reduce the
problem of high border-surface ratio in small plots, individuals or pairs located less than 50 m from the plot border have been counted as half an individual or half a pair since part of their home range probably lies out of the
plot. Test censuses were performed in March of 1985 in order to become familiarized with the plots, and then real censuses were performed monthly
from April 1985 to April 1987, always by the same person (G.L.I.). The data of
the two census days of each month were combined to obtain a density estimate per month in each plot.