Growing evidence that individuals of many generalist animals behave as resource specialists has attracted substantial research interest for its ecological and evolutionary implications. Variation in resource preferences is considered to be critical for developing a general theory of individual specialization. However, it remains to be shown whether diverging preferences can arise among individuals sharing a similar environment, and whether these preferences are sufficiently stable over time to be ecologically relevant. We addressed these issues by means of common garden experiments in feral pigeons (Columba livia), a species known to exhibit among-individual resource specialization in the wild. Food-choice experiments on wild-caught pigeons and their captive-bred cross-fostered descendants showed that short-term variation in food preferences can easily arise within a population, and that this variation may represent a substantial fraction of the population foraging niche. However, the experiments also showed that, rather than being limited by genetic or vertical cultural inheritance, food preferences exhibited high plasticity and tended to converge in the long-term. Although our results challenge the notion that variation in food preferences is a major driver of resource specialization, early differences in preferences could pave the way to specializations when combined with neophobic responses and/or positive feedbacks that reinforce niche conservation.

This dataset includes information on replicated food-choice assays in a common garden framework using pigeons from two wild populations and their captive-bred descendants—half of them cross-fostered between nests. 

Captures and husbandry of wild-ranging pigeons. We captured 42 adult feral pigeons (Columba livia) from two free-living populations located 50 km apart, one in Barcelona (BCN hereafter; DD coordinates: 41.38879, -2.15899, n = 23 pigeons) and another from Moià (MOIA; 41.81112-2.09839, n = 19). The two populations showed substantial differences in their foraging ecology, with individuals from BCN spending more time actively searching for food than those from MOIA, which instead rely more on sit-and-wait strategies (Sol 2008). After capture, individuals were measured (wing, tail, tarsus and beak lengths), banded with a unique combination of colored rings, and randomly assigned to four outdoor aviaries of 2x4x2 m (8-12 individuals from the same population) for acclimatization. Each aviary was provided with roosting sites, water and ad libitum food (a commercial mixture of food, including the six food types subsequently used in the assays; see below). All animal care, husbandry, and experimental procedures were in accordance with the Spanish code of practice for the care and use of animals for scientific purposes and were approved by the Generalitat de Catalunya (0152S). Individuals were released at the end of the experiments.

Food-choice experiment.  For the food-choice experiments, individuals were relocated in individual cages of 70x50x40 cm containing a feeder and a watering bowl. Experimental cages were located indoors, to homogenize the conditions in which assays were conducted. During assays, birds were observed from behind a blind to avoid disturbance by the observer. Six individuals were tested simultaneously, assigned at random within each of the four outdoor aviaries. Experiments were videotaped and behavior was scored using the software Jwatcher (https://www.jwatcher.ucla.edu/). We conducted food choice experiments in two sessions, one after acclimatization (between 1 and 1.5 months after capture), and another a year after to estimate long-term consistency in food preferences. To assess food preferences of individuals, we presented each pigeon with a six-section circular Plexiglas feeder containing 10g of six different seed types (green peas, oats, popcorn maize, soybeans, sunflower seeds, and wheat), an amount large enough to avoid being depleted during the trial. The six food types were part of the diet of pigeons during the acclimation period, and they were chosen to provide variation in size and nutritional contents. In each trial, the position of the different food types in the container were randomized (to avoid spatial biases in the choice), and individuals were allowed to feed for 20 minutes. After this time, we removed the feeder and measured the amount of each food remaining with a digital precision balance. The amount of each seed type consumed per individual was estimated by subtracting this quantity from the initial 10g. Nine trials in which individuals did not eat were excluded from the analyses. To evaluate the consistency in the measure, each individual was tested in a battery of 4 trials conducted in two consecutive days. In the first daily trials, individuals were tested under food-deprived conditions whereas in the second they had already eaten. Thus, our experimental design allowed us to assess the extent to which fasting influenced food choice (Moon & Zeigler 1979). For some individuals, long-term consistency in food preferences was evaluated by repeating the food choice experiment approximately a year later.

Cross-fostering experiment. Between the first and second food choice assays, we separated 16 breeding pairs and placed them into breeding cages with material to build the nest and ad libitum mixture of food. We used pairs that were spontaneously formed in the aviaries (i.e. belonged to the same population), but we removed eggs for a few weeks to ensure male paternity. Because pigeons lay almost invariably two eggs (Johnston & Janiga 1995), we randomly cross-fostered one of the two chicks. Nestlings were cross-fostered when two days old, ensuring that age difference with their new brother was less than two days. Captive raised juveniles were tested for food preferences in three occasions (N = 144 trials in total) once they were 3 months old, following the same protocols used for adults, and then moved together with their parents to the original outdoor aviary of the latter. One year after, most of these youngsters were tested again in three occasions to assess the stability in their food preferences.

Johnston, R. & Janiga, M. (1995). Feral pigeons. Oxford Univesrity Press, New York, USA.

Moon, R.D. & Zeigler, H.P. (1979). Food preferences in the pigeon (Columba livia). Physiol Behav, 22, 1171–1182.

Sol, D. (2008). Artificial selection, naturalization, and fitness: Darwin’s pigeons revisited. Biol J Linn Soc, 93, 657–665.

The file contains three datasets: 1) Results of the food assays (amount of food consumed by individual during the trial, in grams); 2) morphology of individuals; and 3) pedigree. Abbreviations: NA denotes that the information was not available.