by parent birds should also be recorded as they may indicate the presence of
dependent young nearby.
Empty nests of species with altricial young which contained nestlings at the
last check should be examined for evidence that fledging has occurred. The nests
of many species of passerine birds are altered in a distinctive way by the presence
of large young about to fledge. Typically the nest rim becomes flattened and
droppings accumulate in the nest cup, on the rim and outside the nest. These
signs are diagnostic of young having at least reached an age close to fledging.
An empty nest which lacks these signs, indicates that the nestlings would have
been too young to have fledged, may be taken to have failed. However, passerine
nestlings may leave the nest prematurely if disturbed and there would then be no
signs of fledging. Well-grown passerine nestlings often leave fragments of the
cylindrical waxy sheaths that enclosed the growing feathers behind in the nest.
This is a sign that nestlings survived to an advanced age before predation or pre-
mature fledging.
The area around an empty nest that is thought to have failed should be
searched for egg or shell remains apparently left by predators. These should be
described carefully for damage characteristics associated with particular preda-
tors and preferably collected for later examination. Rigid cardboard or plastic
cups with lids can be carried for this purpose. Subtle signs, such as the paired
pinpricks left in the shell of some eggs taken by mustelids, are easier to find in
a room with the help of a bright lamp and it is often useful to compare egg
remains with others you have collected previously. Keeping eggshell remains
also makes it possible to show egg remains to an expert on the signs left by a
particular predator and compare toothmarks with the skulls of potential
predators.
3.3.5Determination of chick survival for species with precocial young
In those species whose young move away from the nest, it is usually difficult
to follow the fates of chicks from a particular breeding attempt. If parents or
chicks are individually marked at hatching or soon after, then mark-recapture
or mark-resighting methods can be used to estimate the number of young that
reach independence (Chapter 5). This can be done by making resightings or
recaptures at regular intervals throughout the period when the chicks are depend-
ent or flightless. However, the design of such studies must take into account the
large movements of up to several kilometres made by broods of some galliform,
anseriform, and charadriiform species. It is easy to mistake movement out of the
study area for death of chicks. Having marked parents as well as chicks helps with
this problem. Parent birds with precocial young often show conspicuous and
64 |Breeding biology