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

摘要

Despite the large number of feral pigeons and their proximity to humans, their use of theudurban habitat is not entirely understood. Previous studies have given various results aboutudthe home range of feral pigeons and their temporal activity patterns. The aim of our study isudto clarify the situation for Basel and to compare it to other cities. For this purpose, weudadapted the global positioning system (GPS) to use it for the first time with feral pigeons.udIn a first step, we tested the suitability of this method for studying the spatio-temporal use ofudthe urban habitat by feral pigeons. Despite some problems due to the highly structured urbanudhabitat such as poor satellite signal reception in the street canyons, and technical limitationsudsuch as short battery life, the method revealed itself to be very suitable.udIn a second step, we studied the behaviour of 80 free-ranging feral pigeons living in threeudlofts situated in the city of Basel.udIn our study, we could prove that pigeons follow individual strategies in using the urbanudhabitat. Some birds covered only short distances (300–500 m), others flew to surroundingudagricultural areas 5 km away from the loft. On average, pigeons in Basel covered longeruddistances than pigeons in many other cities. These differences may partially be due to theudmethod applied. Contrary to other methods, GPS-tracking records all displacements. Theuddifferences probably also depend on the availability and distribution of food resources in theudcities. The pigeons of each loft visited one or two principal feeding places, but used alsoudother places on a less regularly basis. The pigeons showed flexible behaviour that enablesudthem to adapt to different situations. Pigeons are not dependent on feeding in the vicinity ofudtheir sleeping or breeding places, as stated by some authors. Our results show that they areudable to fly a few kilometres to search for food. Death from starvation is, therefore, not audvaluable argument against pigeon control campaigns which are based on reduction ofudintentional feeding. Our findings are also important for biomonitoring projects using feraludpigeons. For statements about pollution indicated by this species, it is generally assumedudthat they show a limited mobility in the city. Our results prove that this is not always the caseudand that the use of the urban habitat must be verified for each project.udIn our study, females covered longer distances than males. Reproduction is much moreudenergy consuming for females than for males. Females also have problems competing forudfood with the stronger males. We therefore believe that females preferred flying longeruddistances to reach more abundant and reliable food sources.udThe home ranges differed between the lofts but showed an overlap at some feeding places.udDiseases and parasites can therefore be transmitted from one subpopulation to another andudspread over the entire city. This is of human concern, since at least seven infectiousuddiseases can be transmitted from pigeons to humans.udOn average, pigeons spent 31.3% of the day outside the lofts. This percentage variedudaccording to breeding state and season. Breeding pigeons spent less time outside than nonbreedingudpigeons or pigeons rearing young and had a different temporal activity pattern.udBreeding is a constraint to pigeon life, not only because it is time consuming, but alsoudbecause temporarily restricted food resources can no longer be exploited by one pigeon ofudthe breeding pair.udEven during short winter days, pigeons spent on average only 28.5% of the day outside. Dayudlength is therefore not a limitation to finding enough food. In autumn, the pigeons spent moreudtime outside than in any other season. We found no correlation with the day length or theudpercentage of breeding birds. We suppose that the pigeons must replenish their fat reservesudafter the energy consuming breeding season, as well as moult, and that they therefore spendudmore time foraging. The evolution of pigeons’ weight over the seasons reinforces thisudhypothesis. The weight was highest in winter, decreased during spring and summer andudincreased again in autumn.udDuring this study, females spent more time outside the lofts than males. We suppose thatudmales must spend more time in the lofts to defend their territories. As stated above, femalesududalso have problems competing with the stronger males for food at unnaturally concentratedudfood sources that are typical for cities. The longer periods of time spent outside may reflectudtheir difficulty to gain access to food.udBefore starting pigeon control campaigns, it is important to know the size of the population.udCensus counts are best undertaken when most pigeons have left their sleeping or breedingudplaces. Our results show that, in Basel, the best time for counts is in the early afternoon,udbetween 12:00 and 14:00, when, on average, 60–70% of the pigeons are outside.udTo sum up, the GPS method allowed us to gather detailed information on the individual useudof the urban habitat by feral pigeons. These findings are important for the three practicaludapplications: biomonitoring with feral pigeons, understanding of transmission of diseases,udand pigeon control campaigns.