DOI: 10.5061/dryad.3j9kd51pq
title: Data from: Feral pigeon roosting and nesting occurrences in MRT viaduct expansion gaps and measured variables in Singapore

description: The feral pigeon (Columba livia) is a globally commensal bird that can
 cause dis-amenities such as soiling and is a potential vector of various
 diseases. Aside to limiting food as a management strategy, reducing the
 availability of roosting and nesting sites can help regulate feral pigeon
 populations. Despite their prevalence, current knowledge of their roosting
 and nesting preferences is lacking. Feral pigeons commonly use railway
 viaduct expansion gaps in Singapore for roosting and nesting. These gaps
 provided an ideal experimental platform to examine feral pigeon roost and
 nest site selection while controlling for differing cavity sizes which can
 significantly affect their reproductive success and site selection
 decisions. We also conducted an in-situ experiment to test the efficacy of
 nest removal as a management option. Our nationwide surveys of 80.3km of
 railway viaducts and 6,048 gaps revealed that feral pigeon day roosting
 and nesting preferences are influenced by structural height and more
 importantly, their proximity to human food sources. There was a
 significantly higher probability of feral pigeon roosting in a gap if it
 had more pigeon feeding incidences in its vicinity and was higher. The
 probability of feral pigeon nesting in gap was higher if it was closer to
 a railway station, lower and further from water bodies. In our field
 experiment, we did not find any significant differences in the proportions
 of the abundances of feral pigeon to other urban commensal bird species at
 the gaps before and after nests were removed. Overall, our results suggest
 that a concerted effort to reduce anthropogenic food availability to feral
 pigeons is central in limiting their reproductive success and controlling
 their population.
description: We conducted our surveys on bird roosting and nesting along all
 above-ground MRT tracks on the main
 island of Singapore (1°21’N, 103°49’E) from January to February 2020 and
 repeated our surveys in March 2020. Nest surveys were not conducted in the
 subsequent survey as the occurrence of new nests between February and
 March 2020 is expected to be minimal. Our surveys were conducted during
 the dry phases of the Northeast Monsoon with less rainfall and coinciding
 with the start of the breeding season for resident birds in Singapore. In
 total, 80.3km of North-South and East-West viaducts amounting to
 6,048 gaps, were surveyed.
 For each viaduct gap, we measured the height of the gap from the ground
 (mean, 6.33m), and recorded the state of deterrent measure used at the gap
 (‘absent’, ‘present’, or ‘damaged’), as well as the presence or absence of
 nesting materials and soiling as an indication of bird usage. We also
 noted the bird species observed in the gap. Surveys were conducted in
 clear weather (i.e., non-rainy days) from 0900 to 1900h. For gaps that
 were inaccessible because the viaduct cut across construction sites or
 private properties, we recorded the height of the gap only, and bird
 species occurring at the gap (~4% of the total number of
 gaps). We observed a total of 2,264
 columns and 6,048 viaduct gaps in 80.3 km of above-ground viaducts. For
 consistency, we only used 1,751 columns that supported four expansion gaps
 for analyses. To minimise spatial autocorrelation, we selected 230 columns
 that were spaced at least 100m apart from each other, beyond the feral
 pigeon natal distance of 90m (i.e., maximum distance travelled by juvenile
 birds from their nests). Only columns that did not have any deterrent
 installed were selected because they may exclude pigeons from using the
 gaps. We aggregated the total number of feral pigeons detected in the four
 gaps of each column to obtain abundance since these gaps were connected.
 Feral pigeon day roosts were defined as gaps where the presence of a feral
 pigeon was recorded in least one of our two sampling occasions (i.e.,
 January-February 2020 and March 2020), and showed an indication of nesting
 or soiling to preclude gaps that were only used only momentarily (e.g., as
 a hideout from a potential threat). The presence of nesting materials in
 the viaduct gaps such as twigs and leaves were used as an indication feral
 pigeon nesting. Any nests that included the presence of bird species other
 than the feral pigeon were omitted from analysis on feral pigeon nesting
 preferences. We selected the following environmental
 and structural factors that may influence day roost and nest site
 selection of pigeons along the viaduct: (a) Intensity
 of pigeon feeding: “Mercy feeding” is a significant food source of pigeons
 in several cities, including Singapore. Data for public feedback cases on
 mercy feeding (i.e., incidences where intentional feeding of pigeons by
 people occurred and were reported by feedback providers) were obtained
 from the National Parks Board (NParks) from January 2019 to January 2020
 (<em>n</em> = 3130) and aggregated within a 300 m radius of
 each column. (b) Distance to nearest hawker centre:
 Hawker centres are food centres housed in open-air complexes made up of
 several small stalls selling cooked food. Urban commensal birds such as
 the house crow (<em>Corvus splendens</em>), Javan myna
 (<em>Acridotheres javanicus</em>) and feral pigeon have been
 found to be attracted to food wastes in the hawker centres. Here, we
 recorded the distance of each column to their nearest hawker
 centre. (c) Distance to nearest water body: Water is
 essential to feral pigeons, particularly during breeding for the
 production of crop milk. Feral pigeons were also observed to nest and
 roost near water points in cities. Water bodies in our study include
 rivers, reservoirs, and large canals. (d) Distance to
 nearest MRT station: MRT stations often have food outlets and their refuse
 collection points could also serve as a food source for feral pigeons.
 Thus, we calculated the distance from each column to the nearest MRT
 station. (e) Mean distance to nearest five public
 residential buildings: We chose five buildings to better represent a
 collective contribution at the estate level as opposed to an individual
 building. Tall buildings are favoured by feral pigeons for roosting or
 nesting on the ledges or roofs to avoid predation and disturbances. Tall
 buildings were also highly correlated to pigeon density in Singapore.
 Here, we focused on public housing buildings, which are homes for most
 Singaporeans and typically range between 20 to 40 storeys high. We
 calculated the mean distance to the nearest five public housing buildings
 as our covariate. (f) Height of MRT viaduct expansion
 gap: A measure of the structural height of the available nesting or
 roosting sites. Feral pigeons tended to nest or roost higher to avoid
 predator and other disturbance from the ground. (g)
 Observation time: We calculated the minutes passed from our earliest
 observation, which was at 0900h, to the time each gap was
 observed.
description: The data files can be accessed by using the following softwares:
 Microsoft Excel or R Studio.