The highlight of Audubon's expedition up the Missouri River was his stay at Fort Union from 12 June to 16 August 1843. Among those accompanying him were John Bell and Edward Harris, who procured two birds near Fort Union that proved to be new to science: Sprague's Pipit (Anthus spragueii) and Baird's Sparrow (Ammodramus bairdii). The third edition of the AOU Check-list gives as the type locality for the latter species “eastern Montana, near Old Fort Union, North Dakota” (American Ornithologists' Union [AOU] 1910). The type locality was changed to “prairie of the Upper Missouri = near Old Fort Union, North Dakota” in the fourth edition of the Check-list (AOU 1931). That change reflected the new practice of quoting a type locality verbatim from the author's original description, adding a restricted locality when possible (AOU 1931). Montana and North Dakota were not admitted to statehood until 1889, and Audubon gave the vague type locality of “wet portions of the prairies of the Upper Missouri” (Audubon 1844:359). The Check-list committee for the fourth edition presumably was content to assign the type to North Dakota because Fort Union occurred there. Deignan (1961:641) followed AOU (1931) but also added “Williams or McKenzie County, North Dakota.” He noted, however, that “the exact locality for birds described from 'Fort Union' is uncertain” (Deignan 1961:474).

Fort Union was active from 1829 to 1867, the original structure being located on the north bank of the Missouri River in what is now North Dakota, about 5 km above the mouth of the Yellowstone River and less than 300 m east of the Montana border (Weist et al. 1980). The journals of Audubon, Bell, and Harris indicate that those men ventured well into Montana several times during the summer of 1843 (Bell 1843, Audubon 1897, McDermott 1951). On the basis of the information in those journals, we argue that the type specimen of Baird's Sparrow was taken in Montana, not North Dakota.

Bell shot the first Baird's Sparrow specimens on 26 July 1843, during a day of bison (Bos bison) hunting between the Yellowstone and Missouri rivers (Audubon 1897). On that morning, Audubon's party forded the Missouri River at Fort Union and headed up the Yellowstone Valley in a horse-drawn wagon, Harris stating that they used “the same road we took on our last hunt” (McDermott 1951:154). The road is first mentioned in Harris's journal entry for 20 July: “We mounted the hills by a middle road between the rivers [Missouri and Yellowstone]” (McDermott 1951:145). Harris mentioned the road again on 4 August, noting that it was “midway between the two rivers” (McDermott 1951:165). On 26 July, the party eventually crossed the “Fox River,” now known as Fox Creek, which enters the Yellowstone River from the west 7 km above Sidney, Montana, and about 11 km west of the North Dakota border. There is no indication that anyone in Audubon's party crossed the Yellowstone River during the hunt. They spent the night near the “Three Mamelles,” which Audubon illustrated in his journal (Audubon 1897). Audubon's drawing clearly depicts the “Three Buttes,” which are located in southern Richland County, Montana, about 30 km west-northwest of the mouth of Fox Creek and 40 km west of the North Dakota border (see Durant and Harwood 1980).

Audubon, Bell, and Harris were caught up in the excitement of the chase during their bison hunt on 26 July. So much so, in fact, that only Bell (1843) mentioned the sparrows in his journal entry for that day (“I killed 3 small finches, or buntings, very similar to the Henslow's Bunting…”). Bell did not say when during the day he shot the birds, or that they were new. The latter task fell to Elliott Coues in a footnote to Audubon's journal, who noted that “Among the 'birds shot yesterday,' July 26, when Audubon was too full of his Buffalo hunt to notice them in his Journal, were two, a male and a female, killed by Mr. Bell, which turned out to be new to science” (Audubon 1897: 116). The discrepancy in the number of sparrows Bell shot apparently results from an error by Audubon, because Harris mentions in his journal entry for 29 July that “Bell killed three finches…which so closely resemble Henslow's Bunting…” during the buffalo hunt of 26 July (McDermott 1951:161).

As they headed southwest toward Fox Creek on 26 July, Audubon's party would have entered what is now Montana very soon after crossing the Missouri River at Fort Union, and they would have remained in Montana until their return to the fort two days later. The Baird's Sparrow specimens could not have been taken in North Dakota unless they were encountered immediately after Audubon crossed the Missouri River that morning. Given that Audubon, Bell, and Harris had crossed the Missouri at Fort Union at least six times before 26 July (Audubon 1897, McDermott 1951), it is unlikely that they would have failed to find Baird's Sparrows previously had the birds occurred so close to the fort. Consequently, we believe that the type locality for this species should be revised to “prairie of the Upper Missouri = eastern Montana near Old Fort Union.”