throats and foreheads of captured nectivorous birds can be used to determine the
flowers visited.
10.2.4 Dropping analysis
Birds produce droppings (a mixture of feces and urine), which can be examined
for hard remains. Although identification of remains is more difficult than stom-
ach contents, stomach flushings, or nestling ligatures, the low level of intrusion
makes dropping analysis useful. Droppings can often be collected from birds
caught for ringing. This is easiest if the birds are held in clean bird bags (other-
wise droppings can be mixed across individuals), and held over a polythene sheet
during ringing. Chicks within the nest often produce dropping sacs for the
parents to carry away, and these are often produced when the bird is handled.
These sacs can be picked up by tweezers.
Droppings can often also be collected in the field. In some cases, such as under
roosts, nests, or perches, we can be confident which species or even which indi-
vidual produced which dropping. For some species, the dispersion of droppings
can be used to help identify them. Lark droppings can sometimes be difficult to
distinguish from those of large finches and sparrows, but groups of 5–10 closely
spaced droppings of the right size on the ground in an open area are very likely to
represent the roost site of a lark because, in most European habitats at least,
species with similar droppings roost off the ground. Rain can rapidly destroy the
droppings of small birds. If you want large samples it is best to search after a spell
of dry weather, but if you particularly want fresh droppings search 1–2 days after
the end of a wet spell.
In most cases it is necessary to watch the adults to be confident that the drop-
pings are of the species of interest. However this is often surprisingly difficult.
One technique is to have two people, with one watching the bird using a
telescope. Once a dropping is deposited, one observer keeps staring through the
telescope at the location of the dropping. The collector walks to behind the drop-
ping and then toward the observer who directs the collector to the location using
arm movements.
Each dropping is then usually scraped into a separate bottle, and frozen or pre-
served in 70% alcohol. If dried the contents are harder to tease apart during
analysis. Freezing solid droppings (e.g. from geese or gamebirds) has the advant-
age that each dropping stays separate and they can be kept together while if
placed in alcohol they disintegrate and must be kept separate. Placing droppings
into 20% potassium hydroxide solution for 20 min will remove uric acid and
particles (Green and Tyler 1989), they can then be washed through a sieve and
stored in 70% alcohol.
236 |Diet and foraging behavior