Grit Ingestion Research Articles

The Ruminant sorting mechanism protects teeth from abrasives

Dental wear due to ingestion of dust and grit has deleterious consequences. Herbivores that could not wash their food hence had to evolve particularly durable teeth, in parallel to the evolution of dental chewing surface complexity to increase chewing efficacy. The rumen sorting mechanism increases chewing efficacy beyond that reached by any other mammal and has been hypothesized to also offer an internal washing mechanism, which would be an outstanding example of an additional advantage by a physiological adaptation, but in vivo evidence is lacking so far. Here, we investigated four cannulated, live cows that received a diet to which sand was added. Silica in swallowed food and feces reflected experimental dietary sand contamination, whereas the regurgitate submitted to rumination remained close to the silica levels of the basal food. This helps explain how ruminants are able to tolerate high levels of dust or grit in their diet, with less high-crowned teeth than nonruminants in the same habitat. Palaeo-reconstructions based on dental morphology and dental wear traces need to take the ruminants' wear-protection mechanism into account. The inadvertent advantage likely contributed to the ruminants' current success in terms of species diversity.

True grit: ingestion of small stone particles by hummingbirds in West Mexico

BackgroundGrit is used by birds mainly for grinding hard food items but can also serve a nutritional role as a source of minerals. Ingestion of grit by birds has been documented primarily in species that feed on seeds and invertebrates. Although feeding mainly on nectar and small arthropods, hummingbirds also ingest grit, but why they do so is unclear. We quantified the number of grit particles in the stomachs of six species of hummingbirds during an annual cycle in a seasonal ecosystem of West Mexico.MethodsWe compared the number of grit particles in the stomachs of different hummingbird species (Mexican Violetear Colibri thalassinus, Amethyst-throated Mountaingem Lampornis amethystinus, White-eared Hummingbird Basilinna leucotis, Rivoli’s Hummingbird Eugenes fulgens, Broad-tailed Hummingbird Selasphorus platycercus, and Rufous Hummingbird S. rufus), and between sex and age categories during the different seasons of a year. To determine if grit was used to grind ingested arthropods, we examined the relationships between the number of grit particles, the biomass of arthropods ingested, and their chitin content.ResultsAlthough species did not differ in the number of grit particles in their stomachs, we found that grit was mostly ingested by female individuals, with only one male of one species (Mexican Violetear) presenting grit in its stomach. We also found that female hummingbirds had grit in their stomachs during the rainy and the cold-dry season (June–February) but not during the warm-dry season (March–May). Our analyses revealed no relationship between the number of grit particles and the amount of ingested arthropods and arthropod chitin content. However, high grit consumption was related to wasp ingestion on Mexican Violetears.ConclusionsOur results indicate that grit is used mainly by female hummingbirds. The seasonal variation in the ingestion of grit by female individuals suggests that it can be used to meet mineral requirements related to breeding; however, this topic needs further exploration. Additionally, the use of grit was proportionally higher in juvenile individuals, suggesting it is used for grinding arthropods during a period of fast development.

RECURRENT INGESTION OF GRIT BY COMMON NIGHTHAWKS (CHORDEILES MINOR)

Grit ingestion is widespread among birds, as an aid for grinding up food and as a dietary supplement of calcium, but is less common among insectivores, especially aerial feeders like nightjars (Caprimulgidae). I report recurrent visits by Common Nighthawks (Chordeiles minor) to a gravel driveway in British Columbia at dusk over a 4-y period. These ground visits were highly consistent (nighthawks landed during 93% of 72 dusk watches) and visits were highly concentrated both in time (95% of time on the ground between 10 and 57 min after sunset) and space (91% of the birds' time was spent in 2 areas comprising only 31% of the visible study site). Birds pecked at the ground in 97% of 198 focal-animal watches. In 43 visits the nighthawks picked up or swallowed some item; in 24 cases this was a small piece of gravel and no other items were identified. Surveys of ground arthropods in the study area over 3 y showed that potential prey were sparse (mean <2 insects m–2) and the most common insects were unsuitable prey (tiny 3-mm ants). I conclude that the only reason for the nighthawks to consistently visit this gravel area was to ingest grit. The gravel ingested was crushed limestone, which might support a calcium uptake hypothesis. Grit ingestion, occurring within a restricted dusk period, might not explain why nightjars often sit on gravel roads at night, which is a major source of mortality for several species. Information on ground behavior in Caprimulgidae is important for understanding their mortality risks and conservation.

Radiocarbon dating and integrative paleoecology (ẟ13C, stereomicrowear) of Eremotherium laurillardi (LUND, 1842) from midwest region of the Brazilian intertropical region

The knowledge on the Pleistocene biota that inhabited the Brazilian midwestern region is scarce and no data on the paleoecology of Eremotherium laurillardi from this region have been published so far. The main objective of this study is to provide information about the age and feeding ecology of that taxon from Goiás state and to compare the results with other localities from the Brazilian Intertropical Region (BIR). Carbon isotope and stereomicrowear analyses were performed in a molariform from the left maxilla found in Piranhas municipality. The results include a14C AMS dating of 32,390 ± 100 (34,705-33,947 cal yr BP), and a δ13C value of −8.99‰, which indicates a generalist diet (BA = 0.96) with similar proportions of C3 (pi = 57%) and C4 (pi = 43%) plants consumed. The stereomicrowear results also suggests a mixed diet, although the high values of scratches could be associated to the significant consumption of grasses. Coarse features on the orthodentine surface indicate possible ingestion of exogenous grit due to the behavior of foraging close to or at the ground. The generalist behavior corroborates previous studies from other localities of the BIR. E. laurillardi from midwestern Brazil possibly consumed higher proportions of shrub/tree foliage, whilst in northeastern Brazil it probably had a dominant diet of C4 herbaceous plants. The distinct feeding behavior is a consequence of different climatic and environmental conditions between these regions during late Pleistocene. Our integrative study was efficient to improve the understanding about the paleoecology of this emblematic ground sloth that inhabited midwest region of the BIR during the late Pleistocene, but additional work is needed for more detailed interpretations.

Dietary proclivities of Paranthropus robustus from Swartkrans, South Africa

Pleistocene Paranthropus robustus fossils from Swartkrans have yielded stable isotope values suggesting some foraging on C4 plants possibly including underground storage organs. Dental microwear texture analysis on P. robustus (SK 6, SK 34 and SK 47) from Swartkrans Member 1 is performed to examine whether tooth surface damage from mastication agrees with prior dietary inferences from carbon isotopes. There is considerable variation in textural characteristics among the P. robustus specimens. Specifically, adult SK 34 stands apart from the two subadult specimens, SK 6 and SK 47, suggesting life history could be reflected in patterns of dental microwear texture characteristics, although seasonality and availability of fallback foods may also explain the variation observed in P. robustus. The fossils all exhibit elevated surface texture complexity, resembling the values for Lophocebus albigena and Cebus apella, and to a lesser extent, Pan troglodytes. Paranthropus robustus is dissimilar to primary folivores, such as Trachypithecus cristatus or folivore-frugivores such as Alouatta palliata suggesting leaves comprised very little of its diet. The textural fill volume of P. robustus differs from that observed in extant primates from tropical forests indicating extreme durophagy, perhaps a function of differences in habitat. Ingestion of extraneous grit on the underground parts of plants and from terrestrial resources, perhaps as fallback foods or as dietary staples, may account for these enamel textural properties and may help explain the mixed C3/C4 isotopic signal in P. robustus.

Evidence of High Tolerance to Ecologically Relevant Lead Shot Pellet Exposures by an Upland Bird

ABSTRACT Upland birds that display grit ingestion behavior are potentially at risk of detrimental effects and death from lead poisoning at trap and skeet ranges and other areas where vast quantities of spent lead shot pellets abound. Because commonly cited force-feeding pellet exposure studies deviate from true field conditions, their results may not reflect true risks faced by upland birds. In particular, studies that use new shot pellets and administer more pellets than would be reasonably ingested, critically interfere with the understanding of actualized pellet exposures. In this study, northern bobwhites (Colinus virginianus), a frequent test species in shot pellet research, were dosed in an ecologically-relevant manner (i.e., with spent shot and with no more than three pellets). Notably, the 56-day post-dosing observation period, during which a battery of physiological measures were recorded, exceeded that of related studies. Despite a sustained suppression of a lead poisoning indicator, the data suggest upland birds can withstand spent shot pellet exposures. Data detected a survivorship ≥95%, absence of illness, demonstrated tolerance for extremely high blood lead concentrations, and unaffected blood parameters. In conjunction with ecological considerations (e.g., spatial scale and animal behavior), concern about bird population losses from the incidental ingestion of spent shot pellets is potentially overstated.

Grit not grass: Concordant patterns of early origin of hypsodonty in Great Plains ungulates and Glires

A major step in mammalian evolution was the shift amongst many herbivorous clades from a browsing diet of leaves to a grazing diet of grasses. This was associated with (1) major cooling and increasing continentality and the enormous spread of grasslands in most continents, replacing closed and open forests, and (2) hypsodonty, the possession of high-crowned teeth. Hypsodonty is traditionally linked with eating grass because of the contained phytoliths, silica-rich granules, which are presumed to wear away mammalian dental tissues. However, we present evidence from the Great Plains of North America that the origins of hypsodonty in different clades of ungulates (hoofed mammals) and Glires (rodents and lagomorphs) were substantially out of synchrony with the great spread of grasslands, 26–22Myr ago (latest Oligocene/earliest Miocene). Moderate hypsodonty was acquired by some Oligocene artiodactyls and several rodent families (mainly burrowers) at least 7Myr earlier. Highly hypsodont ungulates and hypselodont (= ever-growing cheek teeth) rodents post-date the spread of grasslands by 4 to 9Myr. Lagomorphs follow a different trend, with hypselodont forms present from near the Eocene–Oligocene boundary. These results indicate that hypsodonty was not a simple adaptation for eating grasses, and may have originated in some clades to counteract the ingestion of grit and soil.

Persistent Increase of Blood Lead Level and Suppression of δ-ALAD Activity in Northern Bobwhite Quail Orally Dosed With Even a Single 2-mm Spent Lead Shot

Birds that display grit ingestion behavior are potentially at risk of lead (Pb) poisoning from mistaken ingestion of spent Pb shot pellets. The majority of available studies designed to assess such risk have used unspent shot pellets rather than field-obtained spent shot, which is oxidized and otherwise changed by weathering. Available studies also often administered more or heavier shot pellets to a bird than it might be expected to ingest. The current study dosed northern bobwhite quail (Colinus virginianus) weighing 194.6 ± 23.1 g (female birds) and 199.3 ± 12.2 g (male birds) with one to three spent no. 9 Pb shot collected from a skeet range, with particular interest in the toxicity that may occur from ingestion of a single 2-mm, 50 mg shot. An 8 week post-dosing clinical observation period was employed, over which feed consumption, body weight, blood Pb levels, and a battery of blood physiological parameters were made. Weight loss occurred in the birds, including male birds dosed with one Pb pellet. Erythrocyte delta aminolevulinic acid dehydratase (δ-ALAD) levels were decreased for the duration of the study across exposures and to levels associated with injury in wild bird populations. Decreased ALAD was particularly severe in female birds dosed with one Pb pellet and was still 92 % decreased at 8 weeks after dosing. Together, these results suggest that inadvertent ingestion of a single no. 9 Pb shot pellet can adversely affect the health of northern bobwhite quail.

EVIDENCE OF TERRESTRIAL DIETS IN PLIOCENE EURASIAN PAPIONINS (MAMMALIA: PRIMATES) INFERRED FROM LOW-MAGNIFICATION STEREOMICROSCOPY OF MOLAR ENAMEL USE-WEAR SCARS

Pliocene papionin monkeys of Eurasia, such as Paradolichopithecus arvernensis, Procynocephalus subhimalayanus, and Macaca sp. indet. from Yushe, are large-bodied and interpreted as at least partly terrestrial. Terrestriality in primates has implications for the dietary items consumed. Dietary proclivities from the evaluation of pit and scratch counts under low-magnification (35×) were inferred to address whether the diets of these Eurasian papionins differ and whether they correspond to extant primates (Papio ursinus, n = 24, Pan troglodytes, n = 9, and Gorilla gorilla, n = 10), three Plio-Pleistocene southern African fossil papionins with known isotopic values (Parapapio broomi, n = 14; Papio robinsoni, n = 10; Theropithecus oswaldi danieli, n = 8), or a Pliocene bipedal hominin (Australopithecus africanus, n = 8). Macaca sp. indet. from Yushe most closely resembles Australopithecus africanus from South Africa, which is characterized by evidence of some hard-object feeding. Paradolichopithecus from Romania and to a lesser extent Procynocephalus from northern India also exhibit use-wear scars associated with the ingestion of grit possibly associated with the exploitation of corms and bulbs of CAM or C4 plants. The dental microwear signal of grassland foraging typical of such C4 grazers as Theropithecus oswaldi danieli does not characterize other Plio-Pleistocene papionins. Pliocene papionin diets converge with those of Australopithecus, suggesting that global climate cooling intensifying during the Pliocene may have led both early baboon-like monkeys and australopiths to increase consumption of nutrient-rich edible plant storage organs in these fragmented and partially open habitats of the temperate Old World.

Use of grit supplements by waterbirds: an experimental assessment of strategies to reduce lead poisoning

The ingestion of spent Pb shot due to confusion with grit or inadvertently with food particles causes Pb poisoning in a large number of waterbirds, this being one of the main causes of mortality for some species. Lead ammunition for hunting is being progressively banned in more countries, while grit supplementation has been proposed as a management measure to reduce the ingestion of deposited Pb shot. Studies of grit selection with waterfowl in semi-captivity and in the wild were undertaken to evaluate preferences in the colour and geochemical composition of grit, whether it was available dry or in water, its position within the wetland and the relationship between grit ingestion and feeding behaviour. Grit ingestion was higher when food was included in the treatments. In the absence of food, red grit was taken in higher amounts than grey in semi-captivity but not in the wild. Siliceous grit was taken in a higher amount than calcareous when offered dry, but not in water. No differences in the amount of ingested grit were found among different positions within the wetland. The number of feeding attempts in plots supplemented with grit was higher than in those without grit, although the highest numbers of feeding birds were found in plots supplemented with food. Grit ingestion in waterfowl is intimately associated with feeding behaviour. To optimize the effectiveness of grit supplementation to reduce the risk of Pb poisoning in waterfowl, calcareous and siliceous grit may be combined and applied in feeding sites or mixed with bait to attract birds.

Lead and Copper in Pigeons (Columbia livia) Exposed to a Small Arms–Range Soil

Small arms-range (SAR) soils can be contaminated with metals from spent copper (Cu)-jacketed bullets. Avian species are particularly at risk because they are exposed to lead (Pb) through ingestion of grit, soil intake from preening, or ingestion of contaminated food near ranges. Examination of the effects of Pb on birds at ranges have mainly focused on intake and toxicity of Pb shot pellets or fragments; however, Pb in soils may be an important pathway of exposure. To evaluate the uptake and effects of Pb from an actual range, the soil fraction (<250 μm) from a contaminated SAR soil was used to dose pigeons (Columbia livia) for 14 days at low (2700 μg Pb and 215 μg Cu/d) and high (5400 μg Pb and 430 μg Cu/d) doses. At the end of the study, blood Pb and erythrocyte protoporphyrin were determined, and tissues were analyzed for Pb and Cu. Results showed that Pb was absorbed in a dose-response manner in blood, tissues, and feathers, and erythrocyte protoporphyrin, a biomarker of early Pb effect, was increased at blood Pb levels >50 μg/dL. Four tissues showed differential retention of Pb, with kidney having the highest concentration followed by liver, brain, and heart, whereas Cu levels were not changed. To examine possible interactions with other metals, amendments of either Cu or tungstate were made to the soil sample. Although these amendments seemed to decrease the absorption of Pb, the results were ambiguous compared with sodium chloride controls. Overall, this study showed that intake of SAR soils contaminated with Pb and Cu causes an increase in Pb body burdens in birds and that the response can be modulated by amending soils with salts of metals.

Probabilistic risk‐assessment model for birds exposed to granular pesticides

For granular formulations of pesticides, direct consumption by birds is generally the most important route of exposure. A probabilistic exposure model was developed that estimates how many pesticide granules a bird ingests and, from that, the quantity of pesticide ingested. This model, referred to as the "granular pesticide avian risk assessment model" (GranPARAM), has input variables not included in current screening-level assessments for granular pesticides, such as proportion of time for which birds forage in the field, grit ingestion rates, attractiveness of pesticide granules compared with natural grit, and proportions of soil particles and pesticide granules in the size range consumed by birds. For input variables that are uncertain, variable, or both, distributions are used rather than point estimates. Monte Carlo analysis is then performed to propagate input variable uncertainties through the exposure model for granular pesticides. The outputs from the exposure portion of GranPARAM are estimated pesticide doses for each of 20 birds of a selected species on each of 1000 fields. The dose for each bird is compared with a randomly chosen dose from the dose-response curve for that species or an appropriate surrogate. If the exposure dose for a bird exceeds the randomly chosen effects dose, the bird is considered dead; otherwise, the bird is assumed to be alive. Thus, the risk output from GranPARAM is a bar chart showing the percentages of fields with 0/20 dead birds, 1/20 dead birds, 2/20 dead birds, and so forth.

Grit Ingestion and Size-related Consumption of Tubers by Graylag Geese

In herbivorous birds the processing rate of food is constrained by gizzard capacity. To enhance digestive processes, many species ingest grit to grind the food. Grit ingestion, however, may further limit the capacity of the gizzard. Graylag Geese (Anser anser) wintering in SW Spain fed mainly on Alkali Bulrush (Scirpus maritimus) tubers, showing a preference for small tubers. This preference may be due to a faster disintegration of small tubers than larger ones inside the gizzard. As larger tubers are likely coarser than smaller tubers, more grit would be necessary to process larger tubers. However, the ingestion of more grit to grind large tubers would be at the expense of ingesting additional tubers because of gizzard capacity limitations. Under these circumstances, there may be an inverse relationship between tuber size and amount of grit ingested to optimize food ingestion. Indeed, we found such a relationship. Grit facilitated the disintegration of tubers. This suggests that relying on some amount of grit to facilitate the grinding of food should outweigh the loss of gizzard capacity to the amount of food ingested.

EPIDEMIOLOGIC INVESTIGATION OF LEAD POISONING IN TRUMPETER AND TUNDRA SWANS IN WASHINGTON STATE, USA, 2000–2002

An observational study was conducted to determine the proportionate mortality of wild trumpeter (Cygnus buccinator) and tundra (Cygnus columbianus columbianus) swans that died during the winters of 2000-02 in northwestern Washington State, USA. Among 400 swans necropsied, 81% were lead poisoned (302/365 trumpeter swans; 20/35 tundra swans). Mortality started in mid-November and peaked from late December through mid-February; swan mortality that was not associated with lead poisoning was uniformly lower throughout the winter months. Lead poisoning was 24 times more likely to be the cause of death in swans found in Whatcom County compared to swans found in other locations in northwestern Washington State (95% CI: 12.7, 47.0). Mortality attributable to lead poisoning was twice as likely in adults as in juveniles (95% CI: 1.0, 4.2). Aspergillosis was documented in 62 trumpeter and two tundra swans, including 37 swans in which mortality was caused by lead poisoning. Males were twice as likely as females to have aspergillosis (95% CI: 1.1, 3.8). Traumatic injuries were documented in 37 trumpeter and seven tundra swans, including seven trumpeter swans with concurrent lead poisoning. Dead swans found outside Whatcom County were four times more likely to have traumatic injuries compared to those found in Whatcom County (95% CI: 1.6, 10.0). Overall, lead-poisoned swans were significantly less likely to have concurrent aspergillosis or traumatic injuries. There was no apparent association between grit ingestion (total mass or mass categorized by size) and lead poisoning or number of lead shot. Not surprisingly, lead-poisoned swans were more likely to have one or more lead shot compared to swans that died from other causes (OR 294; 95% CI: 92, 1,005); lead-poisoned swans were also more likely to have one or more nontoxic shot compared to swans that were not poisoned (OR 63; 95% CI: 19, 318). The source(s) of shot are unknown but likely are in or near Whatcom County, Washington.

Heavy metals in livers of waterbirds from Spain.

Wetlands tend to accumulate heavy metals from local sources, such as Pb shot used for waterfowl hunting, and from regional sources, such as atmospheric deposition and riverine or marine inputs. We determined concentrations of six heavy metals (Cr, Mn, Cu, Zn, Cd, and Pb) in livers of waterbirds shot by hunters in five Spanish wetlands to study the different factors that can contribute to the accumulation of these metals (sex, age, diet, grit, and Pb shot ingestion). Differences among wetlands were observed only for Cr, Cu, and Cd. Differences among species were observed for all the metals, and Cu was notably higher in pochards (Aythya and Netta genus) than in other waterfowl. Cu, Zn, and Cd concentrations increased with age, and only Pb showed differences related to sex, with males having higher concentrations than females. Most metals other than Pb were correlated with each other. Lead was dependent on Pb shot ingestion. Grit ingestion positively correlated with concentrations of Cr and to a lesser extent with Mn, Zn, and Cd. Ingestion of grit or shot may obscure relationships between metals and diet. Herbivorous species, which had more grit in the gizzard, had higher Cr, Zn, and Cd concentrations. Granivorous birds, which have the highest rates of Pb shot ingestion, had the highest concentrations of Pb. Grit and Pb shot ingestion are both important sources of heavy metals for waterbirds. Lead was the single metal studied whose concentrations exceeded toxicity thresholds.

Determinants of Lead Shot, Rice, and Grit Ingestion in Ducks and Coots

We investigated the relationships between lead shot ingestion, grit size selection, bill morphology, and diet in a community of 8 duck species and common coot (Fulica atra) wintering in the Ebro Delta, Spain. There were no intraspecific differences related to sex or age in grit composition, lead shot, and rice-grain ingestion. Strong interspecific differences were recorded for all these variables and for the density of bill lamellae. The proportion of grit of size >1 mm (especially >2-3 mm) was positively correlated with the prevalence of lead shot ingestion, as well as with rice ingestion. Rice ingestion was also positively correlated with the prevalence of lead shot ingestion. Those duck species feeding on rice had larger grit and higher prevalences of lead shot than herbivorous species. Contrary to the predictions of a straining model for food or grit ingestion, lamellar density did not explain interspecific differences in grit selection, rice ingestion, or prevalence of lead shot ingestion. These findings contradict previous claims in the literature, and suggest that mechanisms other than straining are used by ducks for grit selection and lead shot ingestion.

Food of the nightjars in Zimbabwe

Jackson, H.D. 2000. Food of the nightjars in Zimbabwe. Ostrich 71 (3&4): 404-407.Analysis of the stomach contents of 282 nightjars (Caprimulgidae) collected in Zimbabwe showed that the seven species concerned feed almost exclusively on nocturnal flying insects, predominantly on beetles (Caleoptera, 52.7%). especially lamellicom beetles (Scarabaeidae, 67.5% of all beetles), and to a lesser extent on moths (Lepidoptera, 12.7%), grasshoppers (Orthoptem, 7.2%). bugs (Hemiptera, 3.5%) and, when available, termites (Isoptera, 20.4%). There is some seasonal variation in diet, and prey selection varies between species. Deliberate ingestion of grit to aid digestion is unlikely.

Toxicological Significance of Grit Replacement Times for Juvenile Mallards

Grit ingestion may be an important exposure route for environmental contaminants in waterfowl. Our objective was to determine turnover rate of grit in juvenile mallards (Anas platyrhynchos) by measuring the time required for juveniles to totally replace grit in the gizzard. To demonstrate the relevance of turnover rate for assessing contaminant exposure, we evaluated the suitability of wetlands receiving oil-sand effluent generated by the mining industry, as viable habitat for waterfowl. Captive mallards were allowed free access to pools of colored grit, the grit color was changed and the time required for color 1 to be replaced by color 2 determined. An exponential relationship between percent grit turnover and time was fitted to the data to obtain a grit turnover rate, k = 0.02/hr. This rate was used to determine amount of contaminants that would be ingested over 21 days by juvenile mallards using oil-sand wetlands as habitat. We demonstrate that grit ingestion could be a significant route of contaminant exposure, specifically for oil-sand related compounds such as oil and grease and naphthenic acids, to waterfowl.

The effects of grit supplementation and feed type on steel-shot ingestion in mallards

Lead poisoning by shot-pellet ingestion is an important cause of death in waterfowl from wetlands that have high densities of lead-shot pellets and low availabilities of grit in their sediments. To evaluate grit supplementation when mixed with baited grain as a method of reducing shot ingestion in waterfowl, 24 mallards ( Anas platyrhynchos) were kept in captivity to study the relationship between steel-shot, grit and grain ingestion in four experiments. Steel-shot ingestion was more related to seeking grit than to feeding on grain, and it did not differ between two types of grain offered (rice or sorghum). Grit ingestion increased with grit supplementation and shot ingestion was only slightly reduced. Calcareous grit used in the experiments had a shorter half-life (1.4 days) in the gizzard than values reported for siliceous grit (3.1 days).

Grit ingestion as a source of metal exposure in the spruce grouse, Dendragapus canadensis

The objective of this study was to determine if ingestion of grit was a source of metal exposure to the spruce grouse, Dendragapus canadensis. A secondary objective was to assess whether grit could provide a supplemental source of essential minerals to their diet. Ca, P, Mg, S, Zn, Cu, Ni, Co, Cr, Fe, Mn, Al, Pb and Cd of liver (adult, yearling, chicks), crop and gizzard contents (adults) were determined for grouse collected from a relatively pristine boreal forest region of north-central Ontario, Canada. With the exception of Cd liver, concentrations were independent of age [one-way analysis of variance (ANOVA); p>0.004). Zn liver concentrations tended to be greater in adults than yearlings and chicks (one-way ANOVA; p=0.02). Liver concentrations of Cd increased with age (r=0.99; p<0.001). The contribution of crop items to total gizzard elemental content was element specific; crop contents contributed 90–100% of Mn and Zn, 70% for P and Ca, 60% for Pb, 50% for S, and 0–25% for Cu, Mg, Ni, Al, Fe, Co, Cr and Cd to the total elemental concentration of gizzard contents (crop plus grit). Incorporation of grit by grouse could, therefore, constitute an important source of essential macro-(Ca, P, Mg, S) and trace elements (Cu, Fe) but not for Mn or Zn. However, in addition to providing nutrients to the bird, ingestion of grit results in exposure to toxic trace metals such as Cd which in turn is accumulating in the liver. Research directed at determining grit turnover time, and hence metal exposure rates, in bird species which ingest grit to aid in food digestion is required. The toxicological significance of Cd exposure to grit-ingesting birds needs attention.