2009 NORTHEASTERN NATURALIST 16(2):177–182 Lead Objects Ingested by Common Loons in New England Mark Pokras1, Michelle Kneeland1, Anna Ludi1, Ethan Golden1, Andrew Major2, Rose Miconi1, and Robert H. Poppenga3 Abstract - Necropsies of Gavia immer (Common Loon) recovered lead and non-lead foreign objects from gastrointestinal tracts. Carcasses collected between 1987 and 2000 reveal that a great deal of loon mortality on lakes in New England is attributable to ingestion of lead objects. In this study, 522 carcasses were examined to inspect the types, sizes, and masses of 222 objects responsible for lead toxicosis. Most ingested lead objects were less than 2.5 cm long and weighed less than 25 g. Information on objects ingested by loons may help in development of non-toxic alternatives. Introduction Lead ingestion by birds has been documented in a wide range of avian species from loons to geese to woodpeckers (Bloom et al. 1989, Locke et al. 1982, Mörner and Petersson 1999, Pain 1990, Wobeser 1997) beginning with Grinnell’s seminal 1894 publication. Ingested lead is most commonly reported to be shotgun pellets obtained by birds while foraging in wetlands. Lead poisoning from ingested fishing gear has regularly been reported in four avian species: Gavia immer (Brunnich) (Common Loon; Locke et al. 1982), Cygnus olor (Gmelin) (Mute Swan; Sears et al. 1989) Cygnus buccinators Richardson (Trumpeter Swan; Blus et al. 1989), and Grus canadensis (L.) (Sandhill Crane; Windingstad et al. 1984). Previous studies of loon mortality have documented significant lead ingestion and elevated lead levels in tissues (Daoust et al. 1998, Pokras and Chafel 1992, Pokras et al. 1992, Poppenga et al. 1992, Stone and Okoniewski 2001). However, sizes and shapes of ingested lead fishing gear have not previously been reported in detail. In the present study, we collected ingested lead objects from the gastrointestinal tracts of loon carcasses to determine the shape, size, mass, and type of objects loons consumed. Information on objects ingested by loons and other wildlife may help to minimize unintended mortalities in the future. Methods Dead Common Loons were collected from the 6 New England states by state and federal agencies, private wildlife groups, and interested individuals. Carcasses were shipped on ice to the Tufts Cummings School of Veterinary Medicine (TCSVM) Wildlife Clinic. We conducted necropsies, collected tissues for histopathology and toxicology, and catalogued food items and objects found within the digestive tracts. We visually classified ingested lead objects by type into six categories: sinker, jighead, split shot, firearms, other, 1Tufts Cummings School of Veterinary Medicine, 200 Westboro Road, North Grafton, MA 10536. 2United States Fish And Wildlife Service, 22 Bridge Street, Suite 400, Concord, NH 03301-4901.3California Animal Health and Food Safety Laboratory, University of California, Davis, CA 95616. *Corresponding author - mark.pokras@tufts.edu. 178 Northeastern Naturalist Vol. 16, No. 2 and unknown. Any objects not easily identified by eye were examined with a dissecting microscope. The sinker category included trolling sinkers, bass casting sinkers, worm weights, or many other shapes of fishing gear used to weight fishing line. We defined jigheads as lead weights of a variety of shapes that had been cast around a hook shaft. The “firearms” category included projectiles such as shotgun shot and bullets. “Other” included lead gear used for fishing that could not otherwise be classified (eg: lead wires or tapes). We placed objects in the “unknown” category if original use could not be determined because of wear, fragmentation, or deformation. We determined the weight of objects using a Pesola® spring scale accurate to the nearest 0.1 g. We defined length as the longest axis measurable, and width as the largest diameter perpendicular to the longest axis. A mechanic type 6911 caliper (Fischer Scientific) was used to measure lengths in mm to the nearest 0.05 mm. We tested objects for lead by using a commercial, buffered rhodizonate dye swab test (LeadCheck® Swabs, Hybrivet Systems, Inc., Natick, MA), a rapid chemical test used for testing painted surfaces in homes and consumer products. Toxicological analyses were performed as described in Sidor et al. (2003). Results Between 1987 and 2000, 522 loon carcasses were collected from New England (Sidor et al. 2003). Of these, 118 had ingested lead objects. Of these 118 birds, 69 were male, 42 were female, and 7 could not be sexed at necropsy due to autolysis or scavenging. All but two birds with ingested lead were aged as adults using plumage characteristics; the other two were juveniles. Of the carcasses without ingested lead objects for which gender could be determined, there were equal numbers of males and females. For intact cadavers with ingested lead, mean weight for females and males was 3.69 and 4.59 kg, respectively. Each of the 118 loons was found to have ingested at least one lead object with many having ingested more than one, for a total of 222 lead objects. Eighty-seven percent of the ingested lead objects were fishing weights, 11% were from firearms, and 2% could not be identified. The majority of the fishing weights (60%) were sinkers or split shot, while approximately one-fifth (19%) were jigheads (Fig. 1). The firearms category of Figure 1 consists primarily of shotgun pellets, but also includes two bullets (one .22 caliber and one of roughly .44–.45 caliber). About 36% of loons with ingested lead had other fishing-related objects Figure 1. Data on 222 lead objects collected from 1989 through 2000 at TCSVM. The “Other” category includes other Pb fishing gear (lead wire, etc.). “Unknown” includes Pb fragments and objects too deformed to identify. The “Firearm” category includes shotgun pellets and bullets. 2009 M. Pokras et al. 179 (mostly hooks, swivels, and monofilament line) present in the GI tracts, with one bird containing 4 swivels in addition to a sinker. Of the 118 loons with ingested lead objects, slightly over half (73) had more than one lead object in their gizzards. Nearly half of the birds with ingested shotgun pellets had either 2 or 3 such projectiles present. Nearly one third of the birds with ingested jigheads had a second piece of lead present; in most cases, this second item was either a sinker or split shot. One third of the birds with ingested sinkers had a second piece of lead present; these second items were roughly equally distributed among sinkers, split shot and jigheads. Length, width, and mass varied significantly among sinkers, jigs, and split shot (Table 1). As expected, pellets were found to have relatively little variation in length or width due to spherical manufacturing conventions. No jig heads recovered from the GI tracts had hooks remaining attached, although partially digested hook fragments were recovered from 31 of the 118 birds. Thus, length measurements of jigs includes only the lead portion. Over 94% of the 222 lead objects ingested were found to be less than 1.0 in. (2.54 cm) in length, and 44% had a length of less than 1.0 cm (Fig. 2). Of all lead objects ingested, 94% weighed less than 10 g (Fig. 3). Discussion In this sample, all adult loons ingesting lead objects also had demonstrable lead poisoning. As piscivores, loons are expected to have a lower stomach pH than that found in herbivorous waterfowl (Schmidt-Nielsen 1997), leading to more rapid absorption of lead from the GI tract. Most lead mortalities occurred on freshwater lakes (Sidor et al. 2003), and the primary lead objects encountered were fishing sinkers and jig heads. Ingestion of small lead objects by adult loons on lakes is the major cause of mortality in our studies (Sidor et al. 2003). The source of the ingested lead is likely fishing gear picked up from lake bottoms, and also ingestion of fish with attached fishing gear. The ingested lead fishing gear primarily represents the smaller sizes and weights available on the market. Burgess et al. (2005) gave mean body weights of healthy loons captured in a mercury study in Nova Scotia as 4.50 kg for females and 5.54 kg for males. This is greater than mean weights for female and male loons with ingested lead in the current study (respectively, 3.69 and 4.59 kg). However, as Sidor et al. (2003) discussed, loons dying from lead poisoning were generally in better body condition and of heavier weight than loons dying of other causes. We have interpreted this to indicate that, although Table 1. Dimensions of sinkers, jigheads, and split shot ingested by Common Loons. Length (mm) Width (mm) Mass (g) Lead object Mean Median Range Mean Median Range Mean Median Range Sinkers 14.03 12.7 4.0–40.2 5.89 5.5 0.3–15.2 4.04 2.4 0.3–25.0 (± 6.47) (± 2.55) (± 4.63) Jigheads 16.53 15.3 5.2–33.6 6.55 6.0 3.0–13.9 3.89 3.2 0.3–18.1 (± 6.58) (± 2.33) (± 3.64) Split shot 5.79 6.1 1.2–9.9 4.85 4.5 1.5–8.13 1.60 1.4 0.3–5.7 (± 2.33) (± 1.68) (± 1.04) 180 Northeastern Naturalist Vol. 16, No. 2 the loons have lost some body condition prior to death, they most likely die fairly rapidly after ingesting lead. Loons ingest stones selected individually from lake bottoms (J. Barr, University of Guelph, Guelph, ON, Canada, pers. comm), presumably to aid in digestion. Loons may ingest lead objects accidentally while collecting gizzard stones. Alternatively, loons may deliberately select lead objects because such objects fit whatever subjective criteria the birds have evolved to choose stones. Such criteria might logically include such factors as size, mass, shape, texture, or taste. In England, Mute Swans treated for lead toxicosis and released have a high rate of recurrence of lead toxicosis implying that the swans may have developed a taste for lead objects (Sears et al. 1989). Reports indicate that both children and cattle develop a taste for lead paint (Sears et al. 1989). Ingestion of baitfish on fishing lines, or of escaped fish with attached fishing gear are other possibilities for accidental lead ingestion. We were called regarding one instance of an angler fishing a small lake with a single loon pair, who hooked a loon when using a live baitfish. He cut the line to free the Figure 3. Distribution by mass of lead objects found in loons. Figure 2. Distribution by maximum length of lead objects and stones found in the ventriculus of loons. 2009 M. Pokras et al. 181 loon. Within a few days, a dead loon containing a lead sinker was found on the lake, but whether it was the same individual bird is unknown. Because of the grinding action of the gizzard and the presence of small stones against which the fishing gear is abraded, we suspect that measured sizes are somewhat smaller at necropsy than at the time they were first ingested by loons. The prevalence of small lead objects being ingested may be a reflection of loon preference, given the comparative sizes of stones ingested by loons. Although stones of various sizes are presumed to exist throughout loon habitat, we found stones in loon GI tracts to be small (Franson et al. 2001). Stones in 132 New England loons had lengths from 5.6 to 23 mm; (Fig. 3). It is interesting to note that while we found lead objects as small as 1 mm, no rocks smaller than ≈6 mm were encountered. A logical conclusion is that rocks smaller than ≈6 mm may be able to be passed out of the gizzard through the pylorus, while even the smallest lead objects may have inhibited gastrointestinal peristalsis and are more likely to be retained. It should be noted that the size of lead fishing gear encountered in the current study shows very close correlation with the sizes found by Franson et al. (2003) in a broad US study, even though the frequency of lead poisoning was much lower in that sample population. One can make the argument that, given what we know about the toxicity of lead to loons, humans, and a wide variety of other species, every effort should be made to utilize non-toxic alternatives and minimize the introduction of lead into the environment. Minnesota provides useful information on sources for non-lead fishing gear (http://www.pca.state.mn.us/oea/reduce/sinkers. cfm#manufacturers). Until the complete elimination of lead for such sporting uses is achieved, a clear understanding of the sizes and types of gear that pose the greatest threat to loons and other fish-eating species will allow us to formulate rational policies for the protection and management of these species. Acknowledgments We would like to thank the many veterinary students and volunteers whose help over the years has made these studies possible. We thank R. Wood, J. McIntyre of Utica College (Syracuse University), P. Spitzer of the Center for Northern Studies, and C. Perry of the US Fish and Wildlife Service for their invaluable advice and assistance. We thank J.C. Franson of the National Wildlife Health Research Center (USGS) and R. Haebler of the Atlantic Ecology Division (US EPA) for their wise advice and encouragement over the years. We gratefully acknowledge financial support from the US EPA, the USFWS, the Wharton Trust, Massachusetts Environmental Trust, the New Hampshire Charitable Foundation, the North American Loon Fund and the Wood Family Trust. Participation of the following organizations has been critical to our study: North American Loon Fund, Loon Preservation Committee of New Hampshire, Vermont Institute of Natural Sciences, Maine and Massachusetts Audubon Societies, MA Division of Fisheries and Wildlife, ME Department of Fish and Wildlife, VT Department of Fish and Wildlife, and NH Department of Fish and Game. We thank the many wildlife rehabilitators and members of the public who went out of their way to send loons for analysis. The Pathology Department of Tufts Cummings School of Veterinary Medicine generously contributed their expertise to this project. 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