Minerals in gastroliths and foods consumed by band-tailed pigeons

Band-tailed pigeons (Patagioenas fasciata) congregate at and use mineral sites (mineralized water or soil) primarily within the breeding range of the Pacific Coast band-tailed pigeon (P. f. monilis), but the Interior band-tailed pigeon (P. f. fasciata) generally does not exhibit this behavior. Differences in supplemental minerals used between subspecies could be explained by differences in the diet (grit and foods) of these birds between their regional ranges. We necropsied 1,169 band-tailed pigeons and sampled 35 primary foods of band-tailed pigeons in the United States range of the Interior (AZ, CO, NM, and UT) and Pacific Coast (CA, OR, and WA) band-tailed pigeons to evaluate regional differences in mineral and moisture in gastroliths and food items, and the association of grit with food items consumed. Grit and food types consumed by pigeons were similar between subspecies, but grit amount varied with foods consumed and food items varied with season and region in association with plant distribution and phenology. Gastroliths contained small amounts (<= 3.3% each) of calcium, sodium, and potassium and were smooth and polished, indicating relatively long-term retention and use primarily in food abrasion. Foods universally contained low amounts of sodium (0-328 ppm), moderate calcium (100-7,250 ppm), and high potassium (4,400-22,600 ppm), but varied somewhat with food type (e.g., acorns, berries, cultivated grains, pine seeds). Moisture and mineral content of grit consumed and foods used by Interior and Pacific Coast band-tailed pigeons did not differ between their regional ranges in explaining differential use of supplemental mineral sites. Band-tailed pigeon's use of supplemental sodium may not be necessary for survival and reproduction because Interior pigeons rarely use supplemental mineral sites unlike Pacific Coast pigeons despite similarities in moisture and mineral content of grit and foods consumed. Band-tailed pigeons are able to concentrate sodium and calcium in crop milk to meet the nutritional needs of hatchlings despite a diet low in sodium and calcium.