(Picozzi 1975). Domestic livestock and wild mammals such as Hares Lepus
europaeusare also attracted to sticks and novelties and hence may disturb
a marked nest. Using natural markers, such as stones arranged in a particular way,
may reduce this problem, but any clue that is distinctive enough for you to use
may also be used by a predator. Although these problems do not always occur,
it seems best to avoid the risk of using visible nest markers whenever possible.
A common solution is to make detailed notes and sketches of how to find the nest
from an easily identifiable existing landmark, such as a bush or boulder. This has
become considerably easier now that hand-held global positioning systems
enable you to navigate quickly to the correct landmark. One way to find the nest
location quickly from a landmark is to use a spotter, a short length of 15 mm
internal diameter plastic pipe that can be attached to a branch distant from the
nest with stout wire. The researcher fixes the pipe and sights through it to the nest
site when it is first found and leaves it set in that orientation so that the nest can
be found at subsequent checks by sighting it again from the landmark bush or
tree (Simon 1998). Sometimes a nest can be very difficult to relocate even when
detailed notes are available. For example, the ground nests of waders in cattle-
grazed meadows are often destroyed by cows standing, lying, or even defecating
on them (Beintema and Muskens 1987). Trampling by cattle can alter the
appearance of the vegetation around the nest so much that it is not possible
to find it to check for signs that the eggs had hatched before the cow trod on
it. Green (1988) overcame this problem by cutting a slit in the turf next to the
nest and burying a strip of aluminium kitchen foil a few centimeters below
the surface. When nest sites were lost, a metal detector was used to find the foil
and nest site.
3.3.4Nest checking
Nest checks can affect nest success by drawing the attention of predators to
the nest or by preventing parents from protecting the nest contents. Sometimes
frequent nest checks have little or no effect on nest success (O’Grady et al. 1996),
but adverse effects on nest success have been detected sufficiently often (Gotmark
1992) that precautions should usually be taken. Disturbance by observers
may have particularly large effects at certain stages of breeding. For example,
in Eurasian Oystercatchers Haematopus ostralegusthe effect on the nest success
of observers keeping the birds away from their nests was more severe during
egg-laying than during incubation (Verboven et al. 2001).
It is often possible to avoid visiting a nest and disturbing the parents by
viewing it from a distance to see whether a parent bird is incubating or brooding.
By looking up with binoculars from the base of a nest tree, it may be possible to
62 |Breeding biology