Why do trains blow whistles at night while traveling thru open land?

Every night I hear the train miles away as it travels through undeveloped land with no traffic or people. Who are they trying to warn they're approaching? It's not just a few toots, it's many long blasts!

Sometimes wildlife and livestock wanders onto the tracks so this is to keep the tracks clear.

In the U.S. it's federal law that trains, day and night must blow the whistles to warn of their approach to cars on small roads that cross the tracks and don't have railway stop bars and signals. There was a time they had to whistle at every crossing, but technology has changed that.

Its because any small animals or people to get away

Well, if you are hearing the same whistle signal each night, say two longs, a short and a long, then the engineer is blowing the required signal when approaching a grade crossing. The whistles carry for miles and miles, even more so when carried on the wind, so, they may be blowing for a crossing you don't know of.

Random toots, or a short succession of sounds, is a warning to people or animals or livestock on the tracks. But, that is not usual, night after night, and always in the same spot.

If it is something that just started, then like as not the train crew has in their possession "Track Bulletins," that instruct them to sound the whistle at some location. This is usually a temporary measure when men and equipment may be working near the tracks. This rarely happens at night, however, so I think it unlikely.

I gotta go with what Hoghead said. If it's two longs, a short, and one more long, then there's a road crossing out there some place.

I worked with a guy some time ago who had a girlfriend near the tracks. He had a whistle (horn) code worked out so that she would know it was him going by. Then they would meet at the next town, ten miles away. It was a lengthy pattern of short and long blasts on the horn. I'm sure that one made people wonder.

The drivers are bound by the regulations to blow the horn if approaching railway crossings or tracks that cross the lines.This is to warn of its approach.
Also if they see cattle or livestock on the line, it warns the animals.

Night air carries the sound further as well.

They love the sound that keeps them awake.

Lead locomotive engineers have to warn of their train's arrival. There could be livestock on the track, small bridges that the train is about to cross, or really anything. In an engineer's training course, he/she is told that if visiblity is ever reduced, by fog, or even darkness, that he/she should blow the horn often, just in case. Also, some area's require the train's engine bell to be on. A quick and easy way to permanently turn on the engine bell is to give a quick blow of the horn. Last but not least, it could be engineers who aren't used to the area being fooled by "dud" whistle posts that teens put there as jokes. When an engineer sees a whistle post, he/she must blow the horn in a specified sequence, (Long, Longer, Shortest, Longest.)

trains blow thw whistle at every RR crossing wether it's busy or not, it's mandatory and if they don't do it, they get in trouble.