Using GPS-loggers, we examined the influence of colony, sex, and bird identity on foraging flight characteristics of black-headed gulls Chroicocephalus ridibundus during the incubation period. We studied tracks of 36 individuals breeding in one urban and two rural colonies in Poland. Birds from both rural colonies performed the furthest flights (mean 8-12 km, up to 27 km) foraging mainly in agricultural areas. Gulls from the urban colony performed shorter flights (median 5 km, up to 17 km) visiting mainly urbanized areas and water bodies. We found that females performed longer flights and their flights parameters were less repeatable compared to males. Males from both rural colonies visited water bodies more frequently than females. In all colonies males (but not females) used habitats unproportionally to their availability in the vicinity. Relatively low inter-individual and relatively high intra-individual overlap in home ranges indicated considerable foraging site fidelity. Individuals specialized in the use of particular type of habitat performed shorter foraging flights compared to individuals using diverse habitats during their foraging flights. Our results indicate diverse foraging strategies of black-headed gulls, including generalists that explore various habitats and specialists characterized by high foraging site and habitat fidelity.

To characterize flights of black-headed gulls breeding in three colonies located across Central and Northern Poland during the incubation period, we used 18 PinPoint-10 GPS store-on-board loggers (1.3 g, Lotek Wireless Inc.) recording time and position. In total, we deployed loggers on one pair member from 37 nests (10 at Bydgoszcz, 16 at Koronowo and 11 at Przykona). We captured birds on nests during the 2nd-4th week of the incubation period using spring traps or loops made of nylon lines.

Loggers were programmed to collect data at 15 min intervals and were used in 2018: 10-26 May at Bydgoszcz, 28 April - 23 May at Koronowo, and 19-31 May at Przykona. After about 48 h from logger deployment we tried to recapture birds and retrieve tags. We successfully recaptured 36 (97.3%) marked birds.

A foraging trip was defined as a trip with at least three positions recorded with a minimum distance of 1 km from the colony. We analysed only flights performed during day hours (4:00-23:00), as some individuals from Bydgoszcz colony were regularly spending nights on the roofs of buildings in the city centre and returning to the colony during the daylight hours.

See more details in the file Read_me.txt