I have written about the construction of skyscrapers in New York City here and about a famous photograph of high-steel workers having lunch here.

I only mentioned the Mohawk in passing in the first answer, but it turns out one of the men in the photo is a Mohawk. He is the man at the center of the image with a cigarette dangling from his lips. His name was Peter Rice and, like most of the Mohawks working on the high steel, was from the Kahnawake (formerly Caughnawaga) Territory in Quebec.

“The Mohawks in High Steel” were the subject of a 1949 article by Joseph Mitchell in the New Yorker. A quotation from an official with the Dominion Bridge Company seems to be the source of the often-repeated assertion that Mohawks lacked a fear of heights:

"The records of the company for this bridge show that it was our understanding that we would employ these Indians as ordinary day laborers unloading materials," an official of the D.B.C. wrote recently in a letter. "They were dissatisfied with this arrangement and would come out on the bridge itself every chance they got. It was quite impossible to keep them off. As the work progressed, it became apparent to all concerned that these Indians were very odd in that they did not have any fear of heights. If not watched, they would climb up into the spans and walk around up there as cool and collected as the toughest of our riveters, most of whom at that period were old sailing‑ship men especially picked for their expe­rience in working aloft. These Indians were as agile as goats. They would walk a narrow beam high up in the air with nothing below them but the river, which is rough there and ugly to look down on, and it wouldn't mean any more to them than walking on the solid ground. They seemed immune to the noise of the riveting, which goes right through you and is often enough in itself to make newcomers to construction feel sick and dizzy. They were inquisitive about the riveting and were continually bothering our foremen by requesting that they be allowed to take a crack at it. This happens to be the most dangerous work in all construction, and the highest paid. Men who want to do it are rare and men who can do it are even rarer, and in good construction years there are sometimes not enough of them to go around. We decided it would be mutually advantageous to see what these Indians could do, so we picked out some and gave them a little training, and it turned out that putting riveting tools in their hands was like putting ham with eggs. In other words, they were natural‑born bridgemen. Our records do not show how many we trained on this bridge. There is a tradition in the company that we trained twelve, or enough to form three riveting gangs."

Mitchell’s article appears to be the first of many in the popular and academic press of the mid-20th century that attempt to tell the story of Kahnawake Mohawks working on the high steel in New York, Michigan, Quebec, and elsewhere.

A 1950 article in the American Ethonology Bulletin entitled “Modal Personality Structure of Tuscarora Indians, as Revealed by Rorschach Test” repeats this “lack of fear” claim:

The preferred vocation for men is in high steel construction. The "iron-workers," as they are called, are the elite; their status would seem to be analogous to that of the "warrior" class in the old days. The danger of this work on high steel, the traveling it entails, and the good pay, make it a proud profession. In competition with the Whites for such jobs, the Indians have a widely recognized advantage: they do not suffer from that mildly phobic fear of high places which affects so many white people.

This article was followed a few years later by an analysis from the anthropologist Morris Freilich. Setting aside the heights issue, Freilich proposed that the nomadic life of the ironworker mirrored the historical division of gender roles in the Mohawk society, making this choice of career especially appropriate for Kahnawake men. Men on the high steel work in small, cohesive units and pass skills from generation to generation. This was seen by Freilich as similar in operation to traditional hunting bands.

This idea of high-steel workers playing the role of the provider for women in the home was taken up in two articles in the Journal of Ethnic Studies in the 1980s. By then, economic issues were understood to be at the core of the Mohawk’s historical involvement in high steel rather than an innate lack of fear—though an appreciation of strength and agility and a culture of risk-taking among Mohawk men were also acknowledged. There was a realization that the decline of traditional employment as voyageurs in the fur-trading industry necessitated the search for new forms of income.*

The construction of the railway bridge on Kahnawake land in 1886 that is mentioned in Mitchell’s article provided a fortuitous opportunity for the Mohawk to begin new well-paying careers working on the high steel. An introduction was all they needed, and in the proceeding decades, generations of Mohawk were involved in the construction of countless bridges and skyscrapers in Canada and the United States, including New York City’s Rockefeller Center, where “Lunch Atop a Skyscraper” was taken in 1932.

*Another demographic overrepresented in high steel construction was men from Newfoundland. It was proposed their lack of fear of heights came from spending a lot of time rigging the sails of fishing schooners. But given the high unemployment and lack of opportunity in Newfoundland at the time, it would seem more practical economic concerns were the motivating factor for them as well.

SOURCES:

Blanchard, David. “High Steel! The Kahnawake Mohawk and the High Construction Trade,” Journal of Ethnic Studies 11:2 (1983): 41–60.

Freilich, Morris. "Cultural Persistence among the Modern Iroquois." Anthropos 53, no. 3/4 (1958): 473-83.

Katzer, Bruce. “The Caughnawaga Mohawks: The Other Side of Ironwork.” Journal of Ethnic Studies 15:4 (1988): 39–55.

Rasenberger, Jim. High Steel: the Daring Men Who Built the World's Greatest Skyline. New York: HarperCollins, 2004.