Hummingbirds expanding range into Las Vegas, NV – the effects of population pressure

                So why does a hummingbird, or any bird, decide to push the envelope and move into a new area, either to nest or to winter? Basically it is the same thing that made the early settlers in the U.S. move west. There were just too many people on the east coast. In the case of  birds, it’s a lack of proper nesting sites and feeding areas. This is called population pressure.

This picture was taken November 18, 2013. The female Anna's Hummingbird was 'owner' of this spot.

This picture taken January 12, 2014 shows they male Costa's Hummingbird who drove away the previous owner. She has never been back to this spot.

                When birds fly south for the winter they often congregate into smaller areas than they summer in. They have less need for space when they do not have to worry about feeding growing babies. Since many of those new birds don’t even make it to the wintering grounds, there is adequate room for the adults. When summer comes, they move north again where they can spread out and have more nesting grounds.

                However there is always competition for the best nesting sites. The more aggressive bird will win out leaving the rest to fend for themselves. Older birds tend to return to the same site year after year. That is their home. Nobody else better try for it. When I lived in the Madera Canyon south of Tucson Arizona, I had a Blue-throated hummingbird who returned every year to the same nest. She simply repaired the old nest from the year before. This nest was on a spike driven into the side of the house under the eaves just for that purpose. If a newbie wanted to come and nest in the Canyon she would have to find another nesting location. If there was no room for her, she was forced to move into a different area. Assuming she was successful with her nest, she would return there the next year, expanding the range of the species. If she failed the range would stay the same.

Lesser Goldfinches at my feeder in Las Vegas NV.

                When I lived in southern Idaho I saw this expansion, not with hummingbirds, but with Lesser Goldfinches. In the many years I lived there I had never seen one of the species. The bird guides showed their range was south of us in Utah and Nevada. Then one year a pair appeared in my yard. The next year it was a small family group of a four or six. The next year it was a small flock. Today, twenty years later, the guide books show the Lesser Goldfinch range as covering all of southern Idaho. They were successful in expanding their range.

                What is interesting is the Anna’s hummingbird actually wintered in this area of the Southwest before they started summering here. My 1966 edition of Golden Field Guide to Birds shows the wintering area of the Anna’s in the desert southwest. Today it shows them as year round residents. I can only assume with the growing population that summer blossoms became abundant enough in the dry, hot Mojave Desert to support their nesting activities and thus they expanded their summering range.

                Range expansion is an ongoing activity for all animals as they constantly push the boundaries looking for new space. For humans this push is still leading them into new space – outer space!