Birds get around. They have wings after all. This diary is about dispersal and in particular dispersal gone wrong. Dispersal in animals refers to a one way move, starting in point A and ending up in point B. This kind of movement is not as appreciated, perhaps, as the annual migrations of birds that we all await anxiously every spring and fall. However dispersal is equally important as that is how birds find a home when they grow up, how bird species expand their ranges as conditions change, and the reason rare bird alerts came into existence.
Imagine a chickadee family, mom and dad, and a handful of chicks in the nest. The parents are defending a territory in woods, keeping other chickadees out so they have exclusive access to bugs and seeds and stuff. When the chicks fledge they can’t stay in their parents’ territory. They need to set out and find their own place. They need to disperse. The parents might also need to disperse if they were displaced by chickadee ruffians from the bad side of the forest or if there was a forest fire.
Again birds have wings. They can potentially disperse quite a long way. One ‘big-picture’ consequence of that is that the geographic distributions of bird species are a lot more fluid than those of many other animals. My first field guide was to the Amphibians and Reptiles of Eastern North America by Roger Conant. The first thing it said about identification was that you should use the range maps to determine what species were present in your area and rule out the others. A (rude) birder would laugh at you for following such a procedure.
Another big picture thing is that birds are really good colonists. They can make it to any oceanic island. Sea birds can find places to breed that predators can’t reach. No forest or grassland or marsh, no matter how remote is free of birds.
This is not to say that having wings is an unmitigatedly good thing. Island birds and island insects often evolve flightlessness. Part of the reason for that is to save energy if flight is not needed. But being blown out to see is also a concern. Dispersal is definitely not something you want to do if you can avoid it. You leave behind known resources: shelter, food, etc. You place yourself at risk of predators who know the area better than you do. You run the risk of ending up somewhere entirely unsuitable. Dispersal sucks!
For every finch that made it to the Galapagos and helped found the lineage of Darwin’s finches there were uncounted numbers of finches that were blown out to sea and drowned. Migratory birds are more likely to wander far from their destination simply because of the distances they cover. And thus they are likely to end up somewhere completely unsuitable.
Which leads us to rare bird alerts, ebird, and the birding obsession with rarity. Birds end up far from home and birders are excited to see them. Some of these birds are just dispersing a bit outside of their normal range and may find their way home again. The reddish egret and the vermillion flycatcher in the photos above are both birds that are outside of their ‘normal’ distribution here in north Florida but they regularly disperse up/out here in small numbers. Despite the fact that a vermillion flycatcher has been wintering in the exact spot these photos were taken for several years this one was still being harassed by photographers (I took these pictures with a spotting scope). On the other hand, the flamingo is the first of its kind to be seen here in decades. It was probably picked up by hurricane Michael in the Yucatan and dumped here. It was at St Marks NWR for at least a couple of weeks but I am not sure of its status after our recent colder weather. Unless it can find its way south it is unlikely to survive the winter here.