Social association of monk parakeets in relation to proximity and relatedness

Monk parakeets are social parrots that live in loose colonies, often building communal nests and breeding cooperatively. Relatives are clustered within nests and within colonies. Data was collected to test the hypothesis that social associations of monk parakeets when away from their nests (foraging, collecting nest material, etc) are driven by either the spatial proximity of their nests and/or by their relatedness. The dataset includes information on the identities of all birds that could potentially associate with a focal bird when away from their respective nests, an index of their association strength (calculated using the simple ratio index), the distance between their respective nests, the dyadic relatedness of the birds estimated using microsatellite genotypes, the number of times the two birds were seen together, and the total number of times the focal bird was observed. Data are separated into different files according to the  year of data collection (2018 or 2019) to avoid pseudoreplication. Additional files exclude data from each year collected at a feeding station; these data files relate to a conservative anlaysis in case the supply of supplementary food affected social associations. An additional file contains data only for birds whose nests were in the same tree; this file was for an analysis of the effect of relatedness on social association while controlling for nest proximity. Finally, a file is also included that contains the 2018 as described above, but with dyads defined by sex (male-male, female-male or female-male). Each data file relates to a specific analysis in the paper. The conclusion is that monk parakeets do have specific social associations with conspecifics, and that these are infleuenced by nest proximity but not by genetic relatedness.

Methods
The field study was conducted in the city of Barcelona, Spain (41.39°N 2.17°E). The main study site encompassed Ciutadella Park (c. 30 ha) and smaller parks and streets with mature trees in the surrounding area up to approximately 2 km away. Birds were individually marked with aluminium leg rings and a unique, light-weight medal attached to neck collars, which are visible through binoculars from up to 30-40 m. Blood samples were also taken.

In 2018 and 2019, we recorded groups of individually-marked monk parakeets away from the nest throughout the breeding season (March-September) in two contexts. First, groups of monk parakeets were recorded opportunistically when encountered in the field site. We used the ‘gambit of the group’, which assumes that all individuals in a spatially and temporally clustered group are associated with one another. Individuals were recorded as being in the same group if they were within c. 5 m of each other and any individuals that joined the group within approximately 2 minutes of the observer encountering the group were included as group members. GPS coordinates, date and time of each group were recorded. Secondly, groups were recorded during observations made at a feeding station containing peanuts and sunflower seeds, situated on the roof of the Museu de Ciències Naturals within Ciutadella Park. These observations were conducted for approximately three hours a week throughout the breeding season following the same protocols. 

Blood samples (maximum 100 µl) were taken from adults and nestlings for genetic sex-typing and to assess genetic relatedness between individuals. Alleles were scored blind to bird identity and sex and individuals were typed at 21 polymorphic microsatellite loci: Mmon01, Mmon02, Mmon03, Mmon04, Mmon07, Mmon09, Mmon10, Mmon11, Mmon13, Mmon14, Mmon15, Mmon16 (Dawson Pell et al., 2020), MmGT060, MmGT046, MmGT105, MmGT030, MmGT071, MmGT057 (Russello et al., 2007), TG03-002 and TG05-046 (Dawson et al., 2010), and CAM-20 (Dawson et al., 2013). Individuals were sex-typed using the sexing marker Z002B (Dawson, 2007).We calculated pairwise genetic relatedness between individuals using Queller and Goodnight’s (1989) coefficient of relatedness (rQG) in SPAGeDi version 1.5 (Hardy & Vekemans, 2002). We used the genotypes of all 142 unique individuals included in our social association dataset to generate allele frequencies.

The nesting tree location of marked birds was determined in two ways. First, we conducted detailed behavioural observations at 10 mature pine trees in Ciutadella Park throughout the breeding season in 2018 and 2019. A total of 113 marked birds were located in these focal trees in 2018 and 103 in 2019. Birds were never observed to enter a nest chamber they were not using for breeding or roosting during our period of observation, so we are confident that birds assigned as nest occupants were residents in that nest and nesting tree. Second, we conducted surveys in the rest of Ciutadella Park and in likely nesting areas up to 6 km from the park in 2018 and 2019. Once marked birds were assigned to a nest, we recorded the nest’s GPS coordinates; all birds in the same nesting tree were assigned the same GPS coordinates with a distance of 0 m between their nests. GPS coordinates were converted to Cartesian coordinates (UTM) for calculations of inter-nest distance in SPAGeDi version 1.5 (Hardy & Vekemans, 2002). We calculated inter-nest distances separately for 2018 and 2019.

Using flock co-membership, we calculated association indices using the simple ratio index (SRI; Cairns & Schwager, 1986), which varies between 0 and 1, with 1 indicating that individuals are always observed together and 0 indicating two individuals have never been observed associating. The simple ratio index is calculated using the following equation:

SRIAB = x / (x + yAB + yA + yB)

in which the SRI between the individuals A and B is defined as the number of observations in which the two co-occurred (x), divided by the number of observations in which they both occurred together or individually, with yAB representing the occasions the individuals were observed simultaneously but apart and yA indicating occasions that individual A was observed without individual B and yB indicating the reverse. We excluded birds observed on less than five occasions and also birds observed in their fledging year because they were still fed by their parents and were therefore likely to be associated with them away from the nest. Only those dyads with data for inter-nest distance and relatedness are included. 

References

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