The video mention the affect of the railway and telegraph but didnt elaborate on this. The main extinction driver was caused people locating nesting areas, messaging crews and organizing harvest. Squabs are fat near fledging and easy to catch. So crews harvested the young at colonies from 1860 to 1870 & shipped them via railroad. They were so effective at finding and harvesting all the young that by 1880 there was a massive drop in numbers. Once the numbers declined enough the species became even more vulnerable since there sheer numbers countered predator/mortality effects. Remaining in small numbers ensured their extinction. Fun fact: they only laid one egg. Not sure if they did multiple broods over a season, but anyway fairly low recruitment rate.