Biology Reference
In-Depth Information
Traits
Black-headed gull
Kittiwake
Table 2.1
Comparison of
breeding traits of
two gulls: the
ground-nesting
black-headed
gull
Larus
ridibundus
and
the cliff-nesting
kittiwake
Rissa
tridactyla
(Cullen, 1957).
Nest site
On ground
On ledge on steep cliffs
Predation risk to nest
High
Low
Adult response to
predators
Take flight early; alarm calls,
attack predator
Remain on nest until predator
close; rarely alarm, weak
attack
Nest construction
Loosely built, shallow cup
Elaborate, deep cup
Nest concealment
Adults do not defecate near
nest
Adults defecate near nest
Adults remove eggshells
Adults do not remove
eggshells
Chick behaviour
Cryptic colouration (brown
with black markings) and
behaviour (crouch or hides in
vegetation)
Not cryptic (white and grey) and
ignores disturbance.
Weaker claws
Strong claws and muscles
for clinging
Leaves nest after a few days
Remains in nest until can fly
(about six weeks)
Runs off when attacked
Does not run off
Vigorous wing flapping
and jumping during
development
Less vigorous movements
Chick recognition
by parents
Within a few days
Not until about five weeks, just
before young fledge
Chick feeding
Parents give food calls to
attract hidden young
No parent food calls
Adults often regurgitate food
onto ground
Adults pass food directly
to young's bill
good sense as a response to this reduced predation pressure (Table 2.1). Thus, adults rarely
give alarms and remain on their nests if a predator flies past. The nest cup is more elaborate
(to retain the eggs on the tiny cliff ledges). There is no need for a safe nest to be camouflaged,
so adults often defecate by the nest (the cliff ledges become splashed with white) and they
do not remove empty eggshells. The chicks are not cryptic, they ignore predators and
