Spatio-temporal use of the urban habitat by feral pigeons (Columba livia)

Despite the large number of feral pigeons and their proximity to humans, their use of the
urban habitat is not entirely understood. Previous studies have given various results about
the home range of feral pigeons and their temporal activity patterns. The aim of our study is
to clarify the situation for Basel and to compare it to other cities. For this purpose, we
adapted the global positioning system (GPS) to use it for the first time with feral pigeons.
In a first step, we tested the suitability of this method for studying the spatio-temporal use of
the urban habitat by feral pigeons. Despite some problems due to the highly structured urban
habitat such as poor satellite signal reception in the street canyons, and technical limitations
such as short battery life, the method revealed itself to be very suitable.
In a second step, we studied the behaviour of 80 free-ranging feral pigeons living in three
lofts situated in the city of Basel.
In our study, we could prove that pigeons follow individual strategies in using the urban
habitat. Some birds covered only short distances (300–500 m), others flew to surrounding
agricultural areas 5 km away from the loft. On average, pigeons in Basel covered longer
distances than pigeons in many other cities. These differences may partially be due to the
method applied. Contrary to other methods, GPS-tracking records all displacements. The
differences probably also depend on the availability and distribution of food resources in the
cities. The pigeons of each loft visited one or two principal feeding places, but used also
other places on a less regularly basis. The pigeons showed flexible behaviour that enables
them to adapt to different situations. Pigeons are not dependent on feeding in the vicinity of
their sleeping or breeding places, as stated by some authors. Our results show that they are
able to fly a few kilometres to search for food. Death from starvation is, therefore, not a
valuable argument against pigeon control campaigns which are based on reduction of
intentional feeding. Our findings are also important for biomonitoring projects using feral
pigeons. For statements about pollution indicated by this species, it is generally assumed
that they show a limited mobility in the city. Our results prove that this is not always the case
and that the use of the urban habitat must be verified for each project.
In our study, females covered longer distances than males. Reproduction is much more
energy consuming for females than for males. Females also have problems competing for
food with the stronger males. We therefore believe that females preferred flying longer
distances to reach more abundant and reliable food sources.
The home ranges differed between the lofts but showed an overlap at some feeding places.
Diseases and parasites can therefore be transmitted from one subpopulation to another and
spread over the entire city. This is of human concern, since at least seven infectious
diseases can be transmitted from pigeons to humans.
On average, pigeons spent 31.3% of the day outside the lofts. This percentage varied
according to breeding state and season. Breeding pigeons spent less time outside than nonbreeding
pigeons or pigeons rearing young and had a different temporal activity pattern.
Breeding is a constraint to pigeon life, not only because it is time consuming, but also
because temporarily restricted food resources can no longer be exploited by one pigeon of
the breeding pair.
Even during short winter days, pigeons spent on average only 28.5% of the day outside. Day
length is therefore not a limitation to finding enough food. In autumn, the pigeons spent more
time outside than in any other season. We found no correlation with the day length or the
percentage of breeding birds. We suppose that the pigeons must replenish their fat reserves
after the energy consuming breeding season, as well as moult, and that they therefore spend
more time foraging. The evolution of pigeons’ weight over the seasons reinforces this
hypothesis. The weight was highest in winter, decreased during spring and summer and
increased again in autumn.
During this study, females spent more time outside the lofts than males. We suppose that
males must spend more time in the lofts to defend their territories. As stated above, females
also have problems competing with the stronger males for food at unnaturally concentrated
food sources that are typical for cities. The longer periods of time spent outside may reflect
their difficulty to gain access to food.
Before starting pigeon control campaigns, it is important to know the size of the population.
Census counts are best undertaken when most pigeons have left their sleeping or breeding
places. Our results show that, in Basel, the best time for counts is in the early afternoon,
between 12:00 and 14:00, when, on average, 60–70% of the pigeons are outside.
To sum up, the GPS method allowed us to gather detailed information on the individual use
of the urban habitat by feral pigeons. These findings are important for the three practical
applications: biomonitoring with feral pigeons, understanding of transmission of diseases,
and pigeon control campaigns.