Screamers: Spurs

Summary: What is it with those spurs? Join Kiersten as she takes a closer look at Screamer spurs.

 

For my hearing impaired followers, a complete transcript of this podcast follows the show notes on Podbean

 

Show Notes: 

“On the Spurs On Birds’ Wings,” by R. L. Rand. The Wilson Bulletin, June 1954, Vol. 66, No. 2.

Birds of the World: https://birdsoftheworld.org

Screamers: https://animaldiversity.org

Music written and performed by Katherine Camp

 

Transcript

(Piano music plays)

Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

(Piano music stops)

Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

The fifth episode of Screamers is the beginning of a few focused on anatomy. We will start off with the fifth thing I like about Screamers, their spurs. The spurs on the wings of these birds certainly set them apart from their closest relatives; ducks, geese, and swans. These little anatomical gems have been fascinating ornithologists for years.

I found a paper published in 1954 in the Wilson Bulletin titled “On the Spurs of Birds’ Wings.” The author, A.L. Rand, describes the spurs of all the Screamers in decent detail. Rand used specimens at the Chicago Natural History Museum for his study. What he found, I have to admit, was quite fascinating and for a paper written in 1954, it was fairly easy to read and understand. I’ve read a lot of scientific papers in my day and this one was a delight. 

The close up inspection that Rand gave the three Screamer species revealed some interesting details. Let’s talk about these details. All species of Screamer have two spurs. These spurs are attached to the metacarpals of the wing, as we have established in past episodes. The first spur, the larger one, is located on the process of metacarpal 1. The process on this metacarpal is used for attachment of the extensor muscles. The second spur is on the distal end of metacarpal 2.  

These spurs are described by Rand as follows, “conspicuous, stout, smoothly tapering, sharp spurs with a slight radial curve.” End quote. The spurs are found on both wings, so Screamers have four spurs. The spurs are made up of a horny material on top of a bone center. The horny material is keratin. Upon close inspection, the spurs of the Screamers showed fine lines around the base of the spurs indicating growth in layers. One specimen had three separate bands which may indicate annual growth.

At one time is was thought that the spur could be used to determine age of the bird through an annual molt, but there isn’t any evidence that this holds true.

Next, let’s look at each species spurs a bit closer. The following numbers are based on the specimens that Rand looked at in the Chicago Natural History Museum, but on average they seem to hold up over time.

Anhima cornuta, the Horned Screamer, spur is triangular in cross section. The spur curves toward the body. All the corners are sharp including the tip. The length of the first spur on the male is 58-61mm and the second spur is 15-16mm. Female spurs are smaller with a length of 50-55mm for the first spur and 11-17mm for the second spur.

Chauna torquata, the Southern Screamer, spur is nearly oval in cross section but has a sharp-edged flange near the proximal edge resembling the triangular spur of the Horned Screamer. The length of the male’s first spur is 30-47mm while the second spur is 13-20mm. The female’s first spur is 35-45mm and the second is 15-17mm. 

Chauna chavaria, the Northern Screamer, spur is smoothly oval in cross-section and is sharp only at the tip. The male’s first spur is 28mm and the second super measures 18mm. The female’s first spur is 30mm and the second spur is 18mm. 

Typically the male’s spurs are longer than females, even though this last example shows the opposite, we have to remember that Rand was looking at only a few specimens at one museum for this paper. 

Current research indicates that Screamers develop the outer portion of the spur at one year of age. Fledglings do not have the outer protrusion of the spur. So what do they use this spur for? The fact that they don’t develop them until they are on their own indicates that they use them for protection or defense. Screamers have been seen in the wild using the spurs during ma ting season to win the right to court a female. Couples are also fiercely defensive of their nests and have been seen using the spurs as weapons against intruders, both intraspecies, other Screamers, and interspecies, anything else dumb enough to come near a Screamers nest.

So, how and why did Screamers develop these spurs in the first place. Wing spurs occur in other bird species besides, Screamers. Yep, that’s right, other bird out there have wing spurs. Most of them are smaller birds than Screamers and have only one spur per wing. Well developed wing spurs actually occur in Family Anhimidae: these are our Screamers, in Family Anatidae (ducks and geese): only 2 species out of the 144 species and they have only one spur, Family Jacanidae (jacanas): only 2 out of 7 species and they have only one spur, and Family Charadriidae (plovers): only 10 out of 25 species and they have one spur.  

The spur on most species is an extension of modification of the process of metacarpal 1 with serves as the attachment area for the extensor muscles. If you feel this bone in almost any species of bird you can feel a point or knob, so all species had the potential to develop a spur. It varies depending on the flight needs of different species. So why did some birds develop this spur?

If we look at the species that have spurs in modern times, most of them nest on the ground, and spend a lot of thier lives on the ground in water or on water. To successfully protect your mate and young you may depend on using your wings as weapons to fight off predators. When these species of bird did that, the presence of this modified bone increased their survival rates, so this could be the explanation for the evolution of the spur in these species. The bone was playing double duty, a base for the muscle attachment and a useful weapon. I think this is just another instance of nature making so much sense. Man, nature is wicked cool.

I hope you were surprised by this close up look at Screamer’s spurs because it is my fifth favorite thing about them.

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

Join me next week for another exciting episode about Screamers.  

    

(Piano Music plays) 

This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.