Objectives

Increasing refuse and poor management of landfills in the 20th century and the habit of people to feed gulls have contributed to the exponential growth of several populations of larids both in Europe and North America. In the Montreal region, over 75,000 pairs of Ring-billed gulls (Larus delawarensis) nest on islands located in the St. Lawrence River, on Rivière des Prairies and more recently on building roofs in industrial sectors. Gulls are attracted at landfills where costly scaring programs must be maintained to reduce the presence of birds.

When traveling back and forth from the colonies to the feeding sites, gulls often fly over residential areas where they may let droppings down causing some disagreements for citizens who ask for control measures. After the breeding season, gulls disperse over large areas where they are often observed on lakes where water contamination is considered a potential health hazard by citizens. Proper management of a species like the Ring-billed gull requires adequate knowledge about its ecology. Until recently, there was little information available on the distribution, movements, habitat use, and the population dynamics of Ring-billed gulls in southern Quebec. The general objective of our project was therefore to study the foraging behavior and population dynamics of gulls living in urban and peri-urban settings within an integrated management framework. Several aspects of the research have been completed whereas others are still being conducted. We concentrate our study on Île Deslauriers in the St. Lawrence River where 45,000 pairs of gulls are nesting but we are also visiting other nearby colonies. The results of this research contribute to a better understanding of the biology of an opportunistic species and are used to make management recommendations that aim at reducing the problems associated with the presence of gulls.

Main results

Distribution and movements of gulls during and after the breeding season

We were interested to know whether individual gulls forage at the same sites or if they were exploiting different parts of the study area. We specifically wanted to know if they were faithful to their feeding sites. We also proposed to study the activity pattern of breeding gulls (frequency and length of feeding trips). Finally, we wanted to determine where gulls disperse after the breeding period to establish their distribution, particularly in relation with the lakes known to be used as night roosts.

Between 2009 and 2011, we fitted 161 birds with miniature GPS data loggers and characterised 1,765 foraging trips within the Montreal area. The birds were captured on their nests, fitted with a logger, released, recaptured 3-4 days later to recover the device and download the data. The units were then recharged and deployed again on other birds. Feeding sites were located between 0.5 and 45 km from the colony with a median of 12 km and return trips reaching 25 km. These data allowed us to delimit the range visited by gulls and to establish the zones at risk during the breeding period. These results area presented in Martin Patenaude-Monette M.Sc. thesis and are used by Cécile Girault for her Ph.D.

During the first year of the study, we observed large-scale dispersal movements of some marked birds. In 2010 and 2011, we therefore fitted 25 birds (2 juveniles and 23 adults) with GPS-Argos PTT. These devices allow tracking of birds over large distances because locations are transmitted via satellites. In addition, the loggers were fitted with solar panels to recharge the batteries, which have allowed us to follow some birds for over three years. Two GPS locations are obtained each day: at noon to get an idea of the feeding areas and at midnight for locating the roosts. Data are sent once a week via satellites. Ph.D. student, Cécile Girault, has found that nearly 75% of the adults undertake post-breeding movements and those individuals are very faithful to their dispersal routes and post-breeding staging sites.

Finally, we have captured 5,850 adults and 3,300 juveniles in different colonies and marked them with individually-coded colored plastic bands. So far, we have tallied over 8,800 sightings of 3,530 individuals through the dedicated work of our students, technicians and volunteer observers. Using the repeated observations of the same individuals within and between years, Cécile Girault has confirmed that Ring-billed Gulls are very faithful to their fall staging and wintering areas.

Habitats used by gulls for feeding and energetic budget

We first wanted to identify the habitats used by gulls for feeding during different periods of their annual cycle. Next, we wanted to update the information about the food habits of chicks and to characterize the food consumed by adults and sub-adults in different habitats. Finally, we proposed to compare the energy content of food consumed by gulls at landfills, in agricultural lands, and in natural riparian habitats. These objectives were achieved by Martin Patenaude-Monette who presented his results in his M.Sc. thesis and in a paper published in PLoS ONE. The detailed tracking of gulls with miniature GPS data loggers during egg incubation and chick rearing has shown that gulls predominantly used agricultural lands (annual crops) located closed to the colony followed by landfills, especially those located further away from the colony where no deterrence program was conducted or those located closer but during periods with no scaring operation. Finally, urban areas and lawns in parks were used as a third choice. Using data from the Argos-satellite tracking devices, Cécile Girault has determined that shopping centers were the most visited habitat after the breeding season in the Montreal area whereas the shores of the St. Lawrence River received the greatest use by birds that dispersed outside the region.

We collected and analyzed over 500 pellets from chicks on the Deslauriers island colony as well as stomach contents of 165 birds (adults, sub-adults and juveniles) collected in the colony, at landfills (culling program), and in agricultural lands. Approximately 70% of items brought by adults to their juveniles were edible refuse (meat, bread, fries and potatoes), 9% annelids (earthworms), 8% insects and 7% vertebrates (small mammals). In agricultural lands, gulls consumed earthworms and spilled grains (corn and soya). We measured the calorimetric values of the different items and found that the diet obtained in landfills had the greatest energy content compared to agricultural lands.

By combining information gathered by the GPS-data loggers and stable isotope analyses in different tissues, Élyse Caron-Beaudoin has found that individuals appear to feed on the same kind of food throughout the nesting period. Ring-billed Gulls are qualified as generalists but some individuals may specialise on specific food types. Her results were published in the Canadian Journal of Zoology

Finally, results of M.Sc. student Veronica Aponte also published in the Canadian Journal of Zoology have shown that gulls that feed in human modified habitats have a lower parasite burden than those that feed in natural habitats like along the shores of the River. She proposed that the increasing use of anthopogenic feeding areas by gulls have probably contributed to a reduction of their parasite load, which may have enhanced their body condition and thus promoted population growth.

Do gulls use social information?

We had proposed to study the mechanisms involved when gulls were actively foraging for patchy and ephemeral food resources using three indicators that could demonstrate the use of public information: foraging trip characteristics, juvenile diet and isotopic signatures found in the primary feathers grown during brood rearing. We submitted the hypothesis that if public information was exchanged, these indices would be more similar for birds nesting in close vicinity than for those located further apart. This study was part of François Racine M.Sc. thesis that was published in the journal Animal Behaviour. He found that information about feeding sites was available because he could predict the final direction that a gull ended up feeding from its initial direction when departing the colony. However, he failed to find that this information was shared among birds while attending their nests. He found that neighbouring nesting pairs did not depart at the same time nor in the same direction. François Racine submitted the hypothesis that gulls could exchange information about the location of food resources when they use other parts of the colony. He proposed that such exchange could take place when gulls are landing along the shore of the island or in shallow water around the colony after leaving their nest. Finally, the isotopic signatures of flight feathers of juveniles allowed us to determine that the diet of young varies with chicks’ age but not the island section.

Assessing the problems caused by gulls

We wanted to evaluate the magnitude and characteristics of the alleged problems related to the presence of gulls. We also proposed to compare the efficiency of different education programs to discourage citizens from feeding gulls. Finally, we wanted to verify whether the use of lakes by roosting gulls could contribute to water contamination.

In collaboration with Sandra Messih of Chamard et Associés, we prepared a questionnaire that was submitted to 405 households located in 3 municipalities (Terrebonne, Mascouche et Repentigny). The results of this survey that are part of Cynthia Moreau M.Sc. thesis indicate that 95% of citizens realised that gulls are attracted by food. As a follow up question, 62% believe that birds find their food in shopping centers and 75% at landfills. The majority (97%) declared that they do not feed gulls. Over half of the respondents (53%) considered that gulls were a nuisance while 28% judged that they were nice birds. A quarter of the citizens who participated to the survey considered that the gull population was overabundant and 52% were preoccupied by their presence. Their main concern was pathogen transmission (75%) and fouling of their properties (29%). Two-thirds believe that a well structured education program could modify people behavior to stop feeding the gulls and to better manage their garbage. Finally, only 17% correctly identified the federal government as the administration responsible for managing this species.

During the fall 2009 and 2010, we conducted weekly surveys at 10 lakes in the Laurentides region (Echo, Bellevue, Descôteaux, Duquette, Pineault, L’Achigan, Aubrisson, Bleu, Connelly, and Maillé) to evaluate their use by roosting gulls. Lake Connelly was the only lake regularly used and a maximum of 3,000 birds was counted in 2009 and 1,500 in 2010. The use of the lakes was thus much more limited than what was anticipated and we speculated that this may be related to the reduced use of the Ste-Sophie landfill and the desertion of the Ile de la Couvée colony. This prevented us to design a study to compare water contamination between lakes used and unused by gulls.

Scaring methods at landfills

We had proposed to compare the efficiency of different deterrence programs at landfills, particularly the use of falconry and culling. We also wanted to test the use of rubber shots as an alternative to lethal steel shots. We submitted the hypothesis that gulls hit with rubber pellets would be less incline to return to landfills and that with time an increasing proportion of birds would avoid these sites. During her M.Sc. degree, Éricka Thieriot worked in close collaboration with Pierre Molina, Falcon Environmental Services and the managers of Waste Management at Ste-Sophie and BFI Canada at Terrebonne. A first paper published in Applied Animal Behaviour Science shows that rubber shots are not effective in deterring gulls from landfills. In another chapter of her thesis, she clearly demonstrated a reduction in bird use at both landfills with a greater reduction at the site with the more intensive program based on falconry. Éricka Thieriot proposed that the efficiency of falconry resulted from the limited access to the food. She observed that gulls spent less than 1% of their time feeding at Terrebonne under the falconry program compared to 15% at Ste-Sophie with the culling program. Managers of both sites have already applied some of our recommendations. Her results on the efficiency ofthe falconry programme has been published in a special issue of the journal Animals.

Population dynamics of gulls

We first proposed to update the information about reproductive output of Ring-billed gulls and to initiate a banding program to estimate annual survival of juveniles and adults. We also wanted to evaluate the acceptability by citizens of different control measures to help managers in taking decisions. Between 2009 and 2012, we followed between 295 and 397 nests on Deslauriers Island and these data are part of Florent Lagarde M.Sc. thesis. He also compared his results with those obtained in 1979 in the same colony. Ring-billed gulls initiate their nests at least one week earlier now than 30 years ago; they have a similar clutch size and hatching success. The only difference in reproductive parameters was a reduction in fledging success and this resulted in a production of 1.2 birds per pair compared to 1.8 in 1979. Florent Lagarde has submitted the hypothesis that the limited access to garbage at the Terrebonne landfill following the implementation of the deterrence program could explain the difference.

This decline in reproductive success seems generalised throughout eastern North America as demonstrated in a paper that we published in a special issue of Waterbirds on gull populations. By using datat from EPOQ (Étude des Populations d'Oiseaux du Québec) based on checklists filled by bird watchers, we have also shown that the Quebec population of Ring-billed Gulls increased exponentially between 1970 and 1990, then remained stable until the beginning of the century followed by a decline of about 15% until 2012.

The banding program initiated in 2009 is well underway with over 9,000 marked gulls. We have cumulated more than 8,000 observations and recorded 75 recoveries of dead birds. A database has been created to manage all these data and to quickly reply to volunteer observers with detailed information about the birds that they saw and reported using the form available on our web site. The participation of a network of observers is essential to ensure the success of our project. Survival analyses are currently being conducted.

After completing his M.Sc. degree, Martin Patenaude-Monette was hired as research assistant to compile all management plans conducted on various species of gulls in different parts of the world. The main conclusions of his assessment were that it is essential (1) to reduce access to food of anthropogenic origin, (2) to prevent the establishment of new colonies, especially on roofs, (3) to maintain monitoring of population size and to evaluate the management measures and (4) to coordinate the management actions of different stakeholders. As part of her survey, Cynthia Moreau asked to citizens which measures should be taken to reduce the problems associated with gulls. She found that 80% suggested that the best approach would be to implement measures that would modify the behavior of people in regards to their garbage management and hand-feeding while 59% requested that control measures be initiated to reduce the number of gulls.

Main conclusions

Surveys conducted by the Canadian Wildlife Service (CWS) are clearly showing that the breeding population of Ring-billed gulls in the Montreal region is either stable or maybe slightly declining. This trend including the fact that gulls are not classified as a migratory bird game species does not allow CWS to consider Ring-billed gull as an overabundant species. Our study has shown a significant decline in the use of the Terrebonne and Ste-Sophie landfills during the last 10-15 years. We are submitting the hypothesis that the population growth has stopped as a result of this reduction in landfill use by gulls. By reducing the availability of food resources required to feed juveniles, fledging success has been reduced and recruitment may have also declined compared to the period when the demographic explosion occurred. Our project also showed that the best deterrence measure was falconry and this should be applied to all landfills used by gulls during and after the breeding period.

Our detailed analyses of gull movements and their diet indicate that landfills with no scaring program and transfer stations are attractive sites because they supply energy rich food resources. It is obvious that a reduction of organic wastes brought to these sites (as a result of composting or biomethanization) would reduce their attraction for the birds. Gulls use agricultural lands early in spring when farmers are plowing and disking their fields and during haying. After this intensive period, the use of agricultural lands is more sporadic. Our project did not include an assessment of the impact of gulls on agricultural lands. However, the area covered by this habitat is so large, that any management measure would be difficult to put in place.

One surprising result from our study is that a significant proportion of adults leave the Montreal area in June after the breeding period. We can speculate that birds from other regions (e.g. Great Lakes) are undertaking a similar dispersal and that some Ring-billed gulls may come in southern Quebec. This makes the management of this species more complex at a local, national, and international scale because some colonies in the Great Lakes are located in Ontario and in the United States. An integrated approach is thus required to manage this species and this could start with a coordinated large-scale tracking program that would shed lights on these post-breeding movements.

A problem that is likely to become more acute in the future and observed elsewhere in North America and Europe is roof-nesting by gulls. More than 2,000 nests were located in 2012 at Ville St-Laurent and Dollard-des-Ormeaux in the west part of Montreal and other sites may still have been undetected. We speculate that birds that abandoned the Île de la Couvée colony near St-Lambert in 2007 or 2008 may have move to these roofs near the Montréal-Trudeau Airport. Specific control actions need to be implemented but there is a risk that birds will move from one roof to another. Ring-billed gulls can live more than 20 years, which means that any actions on nests will need to be repeated for a long period (15-20 years). Our satellite tracking of gulls has shown that Ring-billed gulls often roost on roofs throughout the Montreal area after the breeding season. The use of roofs for nesting by gulls needs to be further studied.

Finally, it is essential to realize that the perception of citizens about gulls vary from one region to the next. People leaving near la landfill or a colony are more affected and are requesting that actions be taken. However, our survey has shown that the sensitivity of the people about gulls may be influenced by their past experience. It is therefore essential to inform citizens about the actual size of the population, the trends, the actions being taken at landfills and the results. For some people, controlling the size of the population by systematic culling is desirable but this is not the point of view of a majority of citizens. In 2011, more than 200 chicks were rescued and brought to a rehabilitation center where they were reared before to be released in the wild. This shows that some people are really concerned about animal protection and that needs to be taken into consideration by managers. In any cases, good scientific information is required before decisions can be taken and management plans prepared.

On-going and future projects

Annual survival

Marie-Claude Murray, M.Sc. student, wants to estimate annual survival of Ring-billed Gulls using capture-marking-recapture models based on the repeated observations of marked individuals and band returns. She proposes to look at the effect of age, sex, and condition of the birds as well as the weather conditions on survival. She will also use historical data from the Bird Banding Office to compare survival of juveniles banded between 1960 and 1994 with survival estimates for the birds marked during her project.  We focus our observations in spring in the colonies where we can easily observe a large number of marked birds. Casual observations are also conducted at sites known to be used by gulls. Finally, we benefit from the collaboration of a network of observers that can submit their observations using a form available on our web site.

Costs and benefits of post-breeding dispersal

A significant proportion of adults leave the Montreal area after the breeding season and we want to determine the costs and benefits of this dispersion. We will first determine whether dispersal influences survival rate. We also want to determine the habitats used by gulls that disperse and those that stay in the Montreal area and compare the energy obtained in these habitats based on our previous study on the energy content of different food items. 

Natal and breeding dispersal

Although Ring-billed Gulls are known to be faithful to their breeding colony, we have observed several shifts among colonies. We even observed marked birds nesting on roofs where no banding has taken place. We first want to document the natal dispersal of juveniles and second we propose to determine the importance and causes of breeding dispersal.

Breeding success on roof-nesting gulls

We are proposing to compare the breeding success of gulls that nest on roofs vs. those that use natural habitats (islands). High temperatures on roofs during chicks’ rearing and the constant disturbance in industrial areas could become an ecological trap for these birds. With our banding program and information of reproductive success, we hope to understand the colonisation process of roofs by nesting gulls.

Citizen education

We want to compare the efficiency of various education programs to convince citizens to stop feeding the gulls either voluntarily (hand-feeding) or involuntarily (garbage mismanagement). Using different municipalities or boroughs as sampling units, we want to compare the efficiency of putting signs in parks or near fast-food restaurants or shopping centers vs. advertisements in local newspapers vs. field crew that will discuss with citizens that feed the birds.

Ring-billed Gull as indicator of the state of the environment

Since 2010, we have been collaborating with Jonathan Verreault, professor at UQAM and Canada Research Chair in Comparative Avian Toxicology. His group is interested by emerging organic contaminants (e.g. flame retardants) and their effects on gulls in relation with their feeding sites.  Some birds tracked with the miniature GPS-data loggers have been euthanized as part of Marie-Line Gentes Ph.D. research project. She found higher concentrations of BDE-209, a congener of polybrominated diphenyl ethers, in males and especially in those that visited landfills or water treatment plants. Her results have been published in Environmental Research Ph.D. student, Manon Sorais, will pursue this study by fixing GPS-data loggers and passive air sampler to the birds.