CASTELIJNS H & DE MAAT B (2018) Numbers and diet of Rock Pipits in the Verdronken Land van Saeftinghe, the Netherlands. LIMOSA 91 (1): 16-29.
We studied numbers and diet of overwintering Rock Pipits in
Saeftinghe, a wetland in the Southwest of the Netherlands.
Earlier estimations of numbers of overwintering Rock
Pipits in Saeftinghe as well as in the Lower Saxon part of
the Wadden Sea were based on sample surveys, but these
estimates were shown to severely underestimate Rock Pipit
numbers when compared with transect counts. The highest
number of Rock pipits in Saeftinghe, 5300-6200 birds, was
present in November. Rock Pipit numbers in Saeftinghe have
been stable for over 20 years.
The diet analysis of overwintering Rock Pipits in Saeftinghe
was based on investigating prey parts in faeces. Potential
prey items were sampled in the pipit's main feeding habitat,
silt creeks, by collecting soil samples. This provided a
reference collection for the determination of prey remains
in the faeces, but also information on prey availability.
Prey parts in Rock Pipit faeces mainly consisted of small
crustaceans Crustacea, small salt-tolerant snails Assiminea/
Ellobiidae, insects and polychaete worms Hediste. Combined
with the data gathered on prey in the soil samples, it is likely
that the birds foraged on Mud Shrimps Corophium volutator,
Dun Sentinels Assiminea grayana and Ragworm Hediste
diversicolor. Although not detected in the soil samples,
insects were also eaten and were probably caught by the
birds in the salt marsh vegetation. Parts of some organisms
were detected in the faeces but were not found in the soil
samples. However, quantities were small, which suggested
their contribution to the diet was probably minor. A
reservation has to be made for Oligochaetes Oligochaeta spp
as these were very common in the soil samples, but cannot
be recognized in faeces as all their parts are digested.
In conclusion, it is likely that the number of Rock Pipits
is seriously underestimated during regular bird surveys.
Assuming the most recent estimation of Rock Pipit
numbers in the Netherlands, Saeftinghe would be the main
overwintering area for the Rock Pipit, with 42-84% of the
birds staying here. We think this is an overestimation and we
believe it is important to conduct transect counts in other
areas as well to get a better estimation of the number of
Rock Pipits wintering in The Netherlands. Even so, Rock Pipits
are apparently able to find sufficient and the right type of
prey to stay in Saeftinghe in high numbers during the winter
[pdf only for members] [dutch summary]