The Condor95~817-830 0 The CooperOrnithological Society 1993 IMPORTANCE OF LANDFILLS TO NESTING HERRING GULLS JERROLDL. BELANT~,THOMASW. SEAMANS,STEVEN W. GABREY,AND SHERI K. ICKES U.S. Department of Agriculture,Denver Wildlife ResearchCenter, 6100 ColumbusAvenue, Sandusky, OH 44870 Abstract. We determined the importance of three landfills to a population of nesting Herring Gulls (Larus urgent&us, 3,250 pairs) on Lake Erie, Ohio, from May-July 1992. Fish was the dominant food ofadults and chicksthroughout the study.Occurrence ofgarbage in the diet of adults and chicks remained low through chick-rearing then increased after fledging.Presence of telemeteredadults at their nest sitesdecreased from incubation through post-fledging,in contrast to their increased presenceat landfills during the same periods. Overall, females visited landfills more frequently and stayed longer than males; however, use of landfills by both sexeswas minimal (~4% of total time) during all periods. Overall, gulls spent 43% and 4% of their time daily at the nest site and landfills, respectively. We estimate ?80% of the time remaining was spent on Lake Erie, presumably to forage. The estimated daily mean number of adult Herring Gulls at the landfills increased from incu- bation (143) to chick-rearing (723) to post-fledging (1,912). We estimate that 5-7%, 12- 19%, and 35-55% of the adult nestingpopulation was presentat landfills at least once during incubation, chick-rearing, and post-fledging,respectively. The population turnover rate of adult Herring Gulls at one landfill decreased50% from incubation and chick-rearingto post- fledging. Significantlymore gulls at the landfills were observed on areasother than exposed refuseand were not actively foraging,suggesting that landfills are important to Herring Gulls for other reasons such as loafing or social interaction. We conclude that landfills are un- important to nestingHerring Gulls when alternate,higher quality food (e.g., fish) is available. The increaseduse of landfills by Herring Gulls during post-fledging,however, suggeststhat gull activity at landfills located near airports could dramatically affect aircraft safety during this time of year. Key words: Herring Gull:food habits;landfill; Larus argentatus;Ohio INTRODUCTION a concurrent increase in conflicts with humans. Populations of several species of gulls have in- These conflicts include transmission of patho- creased throughout North America and Europe gens and parasites through contamination of wa- in recent years (Harris 1970, Spaans 197 1, Drury ter sources (Mudge and Ferns 1982) damage to and Kadlec 1974, Conover 1983, Blokpoel and buildings (Bradley 1980, Vermeer et al. 1988, Tessier 1986). Suspected causes for these in- Belant 1993), and a hazard to aircraft at airports creased populations include the protection of (Blokpoel 1976, 1983; Dahl 1984; Sherigalin breeding colonies (Kadlec and Dntry 1968, 1990). Therefore, there is critical need for data Spaans 197 l), an increase in nesting habitat from on the influence of various types of landfills have the creation of dredge disposal islands (Patton on gull activity and the importance of landfills and Hanners 1984), and exploitation of landfills to gulls. by gulls as dependable sources of food (Verbeek Although there is general agreement that pu- 1977,Burger 1981,Patton 1988,BelantandDol- trescible waste at landfills contributes to the beer 1993). overall diet of Herring Gulls (Larus urgent&us; Sanitary landfills frequently attract large num- Kihlman and Larsson 1974, Horton et al. 1983, bers of gulls and other birds, at least seasonally Pierotti and Annett 1987, Patton 1988, Pons (Horton et al. 1983; Patton 1988; Belant, unpubl. 1992), there are conflicting conclusions from pre- data). Because landfills are often located near ur- vious studies regarding the importance of land- ban areas, their increased use by gulls has caused fills to gulls during the breeding season. Several authors have suggested that the availability of I Received 12 February 1993. Accepted 28 April garbage increases (Kadlec and Drury 1968, Hunt 1993. 1972, Pons 1992), or is essential for (Sibley and Z Presentaddress: Great LakesIndian Fish and Wild- McCleery 1983), reproductive success. In con- life Commission, 1908YzWest SuperiorStreet, Duluth, MN 55806. trast, Pierotti and Annett (1987) have suggested 18171 818 JERROLD L. BELANT ET AL. LAKE ERIE HERRING GULL NESTING COLONIES LANDFILL ERIE CO. LANDFILL - FIGURE 1. Locationof threemixed solid wastelandfills in relation to nestingcolonies of Herring Gulls in SanduskyBay, Lake Erie, Ohio. that garbage is a low-quality food compared to Three mixed solid waste landfills are located other “natural” foods, and could reduce repro- within 36 km of the nesting concentration (Fig. ductive success. 1). The Erie County Landfill, 7 km south of Lake The objectives of this study were to determine Erie and 19 km southeastof the nesting concen- food habits, flight patterns, and population dy- tration, averaged 275 metric tons of refuse per namics at landfills of adult Herring Gulls and day during the study. The Ottawa County Land- their chicks during incubation, chick-rearing, and fill, 2 km from Lake Erie and 28 km northwest post-fledging periods. Our goal was to determine of the nesting concentration, averaged 563 met- the importance of landfills to a population of ric tons of refuse per day, May-September 199 1. nesting Herring Gulls. The Huron County Landfill, 30 km from Lake Erie and 35 km south the concentration, aver- STUDY AREA aged 84 metric tons per day during the study. At The study was conducted in north-central Ohio each landfill, refuse was spread and compacted from 1 May-3 1 July 1992. The Herring Gull throughout the day, then covered with soil at the nesting concentration (one of the largest on the end of the workday using bulldozers. Each land- Great Lakes, 4,250 nesting pairs in 1989) is lo- fill generally had ~0.5 ha of exposed refuse on cated on Sandusky Bay, Lake Erie (Dolbeer et any given day. These were the only landfills with- al. 1990, Fig. 1). The gulls nest on Turning Point in 40 km of the nesting concentration. Island (TPI), coal piles, and breakwalls and have recently expandedto rooftopsin Sandusky,Ohio. METHODS TPI is a 2.7-ha dredge disposal island created in Population censusand reproduction, We deter- 1900 and is bordered by riprap (Scharf et al. mined the adult breeding population of Herring 1978). About 50% of the island has herbaceous Gulls by conducting two complete ground counts vegetation. Dominant shrub and tree speciesin- of nests containing 2 1 egg on TPI, coal piles, clude red mulberry (Torus rubru), red-osier dog- and breakwalls between 1 and 21 May. Nests wood (Corms stolonijkra), and eastern cotton- with 2 1 egg on rooftops were counted weekly wood (Populus deltoides,Scharf et al. 1978). form early May to early July. The largestnumber HERRING GULL USE OF LANDFILLS 819 of nests counted in each area was combined to abdominal feathersby applying 4-5 ml of a mix- obtain a total count of nests for the population. ture of rhodamine-B dye and silica gel to one or We individually marked 110 three-eggclutch- three eggsof each clutch or by using a dummy es on TPI using 0.6-m wire surveying flags and egg (Belant and Seamans, in press). We applied checkedthem one to two times weekly until eggs the dye mixture to 535 clutches between 1 and had hatched, were destroyed, or considered 13 May, thus marking 16% of the nesting pop- abandoned or inviable (eggs not hatched 26 ulation. Becausegulls were marked over a two- weeks after our initial visit). Nests on rooftops week period, for data collected during observa- were also individually marked using wood blocks tions conducted at the landfill (see below), we and monitored weekly using the same criteria. adjustedthe proportion ofthe population of nest- We defined hatch successas the number of eggs ing gulls color-marked after each dye application. hatched divided by the total number of eggslaid We captured nesting Herring Gulls on TPI us- for TPI and rooftops. Mean hatch date was es- ing walk-in traps (Weaver and Kadlec 1970). We timated by interpolation based on the date of the measured head and bill length, and bill depth of previous check, the number of eggs that had captured individuals to determine sex (Fox et al. hatched or were pipping, and the relative age of 198 1). Each of 20 gulls received a U.S. Fish and chicks(Kadlec et al. 1969). We defined the length Wildlife Service leg band and a radio transmitter ofincubation and chick-rearing periods as 28 and (Advanced Telemetry Systems,Inc., Isanti, MN) 42 days before and after mean hatch dates, re- with a backpack harness made of 6-mm-wide spectively (Kadlec et al. 1969, Drent 1970, Hay- teflon ribbon. The completed radio package cock and Threlfall 1975, Pierotti 1982, Paynter weighed 30 g, or about 3% of the mass of an 1949). Post-fledging data were collected through adult Herring Gull. We did not apply the dye 31 July. mixture to eggsof telemetered gulls. Food habits. We collected food remains and Telemetry. We estimated locations of 17 tele- pellets of undigested material found 5 1 m from metered gulls (nine females, eight males) that nests. Food remains and pellets were collected successfully hatched e 1 egg using standard on TPI, rooftops, and breakwalls. We recorded ground and aerial telemetry techniques (Mech date and location for each sample collected.Food 1983). Ground telemetry was conducted2 3 times items were collected once or twice each week each week and aerial telemetry was conducted from 4 May-14 July. once per week between 07:30-17:00 hr, weather We also collected boli from chicks on TPI one permitting. For ground telemetry, all receiver lo- to two times weekly. Chicks were captured op- cations were plotted using Universal Transverse portunistically by hand or with a net.