PIGEON SOCKS and other preliminary results.

it's been about a year since the initiation of the this project and without getting too sentimental... I've come a long way.

I have visited some of the world's greatest museums and studied in two zoogeographic regions (the neotropics and the nearctic) and seen species I had never encountered before (such as the curly-tailed lizard and Bahamian cave swallow).

if I keep going, I will get sentimental, so without further ado, here is what I have found about pigeon evolution so far:

The central question for this study is: "are feral pigeons in North America evolving?", and from the data I have compiled at this time, I can reply "it is very likely that feral pigeons in North America are evolving". Of course, my research, or any scientific research for that matter, cannot, persay, prove anything, but can support it through evidence.

From the evidence I have collected and observations I have made, here is what can be supported about pigeon evolution in North America.

For a bit of context, I carved 4 study groups out of the regions I have studied. region one is made up of Chicago and the surrounding areas (specimens from the field museum). Regions two is comprised of Maine, south to Connecticut (specimens from Castle Island, Freeport and Avian haven). Region 3 is New York City south to Maryland (specimens from The Smithsonian, the American Museum of Natural History, academy of natural sciences in Philadelphia, Rio Grande, Cherry Grove and Arundel). Region four is North Carolina south to the Florida Keys (specimens from the North Carolina museum of natural sciences, Folly Beach and Key West).

Elongation of leg feathering "grouse" in region two:

One of the most striking things I found evidence to support was the elongation of leg feathering, grouse, or PIGEON SOCKS in region two, or what normal people call New England. After a bit of math, I came up with the following graph:

 

For those unfamiliar with statistics (long may live your blissful ignorance!) this graph might take a bit of explaining. the numbers on the columns are the average values of leg feathering, although included, this is not the most important part of the graph. the real important thing is the capital "I" shaped lines above the columns. These are error bars, and show how much variation exists from the average values. For regions 1, 3, and 4, the values are so variable and close to each other, they could all technically have the same values.

Region two, however, has values so high they are set apart from others, and therefore, statistically speaking, these vales are distinct.

who am I kidding though? you just want to see cute PIGEON SOCKS and fööt flööf and I don't blame you..... pigeon socks are quite adorable.

 

smooth socks!

 

Shaggy socks!

 

scraggly socks !

 

socked pigeon looks upon thee with scorn

The question all of the sock-age brings is, why? most pigeons in southern regions have very short, or no grouse at all, and not present at all in true wild pigeons in Eurasia. in captive pigeons, however, this is a common trait, bred for by humans for pure looks.

 

a "true" wild pigeon in Israel, note the bare legs

 

a domestic pigeon with heavily feathered legs.

What then, would give a New England feral pigeon evolutionary reason to develop an intermediate of these forms? One possible answer is a that these feathers help shield the bird's delicate legs from frostbite or other heavy cold exposure experienced in the harsh region they inhabit. this however, is just a guess, as little research has been conducted on why any bird has feathered legs.

For natural selection to increase the frequency of a trait, it must provide a benefit that increased the individual's or population's evolutionary fitness (frequency of breeding). If feathered feet are used as an insulator, they may aid in increasing a pigeon's fitness. why? pigeons, although they can certainly fly, much of their lives are spent on the ground foraging for food. A pigeon with damaged feet can survive in most conditions, but in the food-scarce winters of New England, any loss in ability to forage might cause starvation, death, and inability to breed.

Sexual selection may also play a role. While natural selection is based off of the fitness of animals that survive, and breed by chance, there's a bit more choice in sexual selection, where individuals are selected to be able to breed by other organisms of the same species.

To be sexualy-selected for in pigeons, You need to have some fancy footwork in the form of the bow-and-coo courtship display:

Here, the male bird spins for a female, a damaged or missing foot would make this difficult, so to be able to breed, intact feet are a must.

 

Some pigeons, like this one found in London, can survive with missing toes and feet. However, these injuries likely come from loose string and hair that cuts of circulation, not frostbite.

Decreased tail length in region three:

If you take what you learned from the last graph and apply it to this one, It should make sense:

 

If you got: The only column with distinct values is column three, you're right!

Tail length is a tricky problem, the lengths of a bird's tail vary through the year based on molt, or "feather shedding" the occurs once or twice a year in most birds. because of this, I needed measurements on birds from multiple time periods for this, and that';s where museums come in as especially helpful.

Because the specimens in museums are deposited all through the year, one can get a rather good idea of the "true" length of a time sensitive feature like a tail by using the average measurements of specimens collected at different times. From this procedure, I was able to find evidence that pigeons in region three have shorter tails than those from other regions.

 

The tail on the left is from a pigeon inhabiting region three while the tail in the right is from region one

The reason for this is less clear than for leg feathering. However, a generally accepted idea about bird tails is that short tails are for speed, long tails are for maneuverability. Even though a pigeon in the heavily urbanized region 3 needs to would weave around buildings to evade predators, they have at least one to need speed:

 

The fastest animal on earth, the peregrine falcon, is one of their main predators.

Shorter tails reduce drag, and increase speed. Of course, going tail-less or seriously reducing the tail length would hinder birds seriously, as some maneuverability is still needed for almost any bird to survive long term.

 

some birds, like this house sparrow, can survive without tails, but will most likely have deceased evolutionary fitness.

Like with the leg feathering, the possible reasons I have provided for tail length variation are mere speculation, but to my knowledge this is a likely reason for this variation.

Increased bill length on regions 2-3:

Bill length is the most enigmatic of the three traits I have found.

 

A combination of region three and four showed bird that have bills less than one millimeter longer than bills from the two other regions. This may not be a true evolutionary trait, one that is heritable, but rather an acquired trait. Because the variation is so slight, the beaks may have been worn down through use, rather than shortened by genetics.

This is a slight difference of course, but still an important one, as it may show how the diets of these populations vary. beaks are often the first thing to change when diets change, so the change in beaks may show something big, I just can't quite figure out.

Sarah Rackowski, over and out.