upon the identification of fragments of cotyledon epidermis in Skylark droppings
(Green 1980).
The main approaches for measuring fruit abundance are
- Visit the same plants regularly and either use a quantitative measure of fruit
abundance and ripeness or mark individual branches and count fruits at
different stages. This shows differences in phenology between species,
individuals, and years (seasonal patterns are reasonably constant in tem-
perate regions but show considerable annual variation in the tropics). - Assess fruit density on the ground. This will pick up broad differences
between sites and indicate timings but is obviously crude and the persistence
on the ground clearly depends upon the abundance of ground dwelling
frugivores. - Place fruit traps (e.g. suspended bags) under the canopy and count the fruit
(usually ignoring aborted fruit) that has fallen. This can provide qualitative
data even where the fruiting trees cannot be seen. However, to obtain
sufficient data for a forest, a large number of traps are needed (75–300)
(Blake et al. 1990). A smaller number of traps are needed if under
individual trees. The abundance of fallen fruit is not the same as the
abundance of fruit available to tree-dwelling birds. - Using transects or point counts (applying methods for bird censuses in
Chapter 2) to assess fruit abundance of a range of plants (Blake et al. 1990).
The availability of food for nectar-feeding birds can be assessed by a combination
of counts of flowers and measurements of the volume and concentration of
nectar in a sample of flowers. Nectar is removed from the flower by probing it
with a microcapillary tube. The volume of nectar is estimated by measuring the
length of the column of liquid in the tube and its sugar concentration can be
measured with a refractometer (Prys-Jones and Corbet 1987).
11.7 Predator abundance
Predator abundance may be important in determining habitat preferences. Fecal
counts are often best for nocturnal mammals or for assessing the abundance of pet
dogs. These may be carried out along a transect of measured length and the number
within a set distance recorded. If the survey is being repeated then the feces are cleared
away to prevent double counting. Creating patches of raked sand and counting
the density of footprints provides a relative measure of mammal density. For most
diurnal bird predators counts along transects (see Chapter 2) are usually the best
approach. Eggs of domestic hens or models of eggs made from modeling clay (see
Chapter 3) can be used to provide some measure of the relative nest predation risk.
Predator abundance| 265