2.2 Nest Tree Characteristics
Characteristics of the nest tree species utilized by
black cormorants, were obtained by measuring 15
trees samped randomly. To avoid the resampling of
the trees, each stands is marked using colored-cloth
ribbons. The nest tree species parameters measured
including:
1. Species of tree used as nesting place
2. H
tree
(tree height) nesting place.
3. H
trunk
, tree height from roots / rhizopor
4. D
tree
, the diameter of the nesting tree, is measured
by using a tape measure on a stem with a height of
1.30 m from the ground or water surface or 10 cm
from the top of the buttress root.
5. N
nest
, the number of nests on one tree
6. Distance
in
, the nest distance to the main stem
7. Distance
out
, the nest distance to the edge of the
canopy
8. Distance
nest
, the distance to the nearest nest in one
nest tree
9. Top, the distance of the nest to the top of the
canopy
10. Distance
edge
, the distance of the nest tree to the
pond
11. Distance
form
, the distance of trees to different
vegetation.
12. N
trunk
, the number of trunk supporting nests
2.3 Nest Characteristics
To determine the characteristics of the nest, 10 (ten)
black cormorant nests were measured. The nest
composition parameters measured including:
- Nest length (cm) is the longest part of the nest
- Nest width (cm) is the widest part of the nest
- Nest depth (cm) is the perpendicular distance from
the inner base
- Nest height (cm) is the distance from the lower
nest to the highest part of the nest.
- Nest edge (cm) is a perpendicular distance from the
nest's mouth to the base of the nest.
2.4 Nest Analysis
All measurement data on variables related to nests
and trees are analyzed using statistical methods
expressed by the average values and standard
deviations.
3 RESULTS AND DISCUSSION
3.1 Nest Tree Characteristics
Tanjung Rejo pond area is a breeding place for water
birds owned by individuals with an area of 4.5 ha.
There are 6 species of water birds inhabit this
location as a place to breed simultaneously. The
water birds found in this location use mangrove
plants that are scattered at the pond location
randomly, according to their body size.
Large-sized water birds will choose locations
difficult to reach by human disturbances in which
located in the middle of the pond position, and
usually not found at the edge of the pond area.
Smaller birds like black cormorant choose to place
nest in random fashion, scattered in all locations
both in the middle and at the edge of the pond area.
The selection of this breeding location by the
water bird found in this breeding location is thought
to be closely related to safety factors to ensure the
success of breeding and survival and the population
of each species, and the strength of the nest tree.
Large-sized water birds need a tree that is
comfortable and strong enough to refute the nest
which will be filled by birdlings and females, while
the smaller cormorants ranging from 58 - 61 cm in
body sizes prefer smaller mangrove trees. The
mangrove trees found in Tanjung Rejo belong to a
small group of secondary mangrove forests.
Black cormorants that breed in Tanjung Rejo
chose to lay their nest only on 4 species of mangrove
trees from 10 species found in this region, namely:
Exocoecaria agallocha, Rhizopora apiculata, R.
mucronata and R. stylosa. This selection is thought
to be closely related to the biological factors i.e. the
size-specific nesting site (Table 1).
The tendency of black cormorantss to choose R.
mucronata is closely related to tree architecture and
nesting habits that are always in groups. Rhizophora
mucronata has many scattered branches and twigs, a
broad canopy and strong branches to support the
nest until reaching 16 nests per stand. (Jumilawaty,
2002).