Bird Diapers
I have only tried one diaper so far. Things didn't work out with that particular duck who thought I was torturing him and I couldn't get him to stop fighting long enough for the diaper to stay on him. So I gave up.
I have two new ducklings : Jenny and Mrs. Gump and I would like them to be friendly, hang out with the humans and be our little mascots. In order to do that, we need to reign in the poop fest. They are still ducklings, but as they are getting older, their poops will also get bigger.
I have Indian Runner Ducks. They stand up straight and are skinny. Diapers made for Chickens or Pekin Ducks don't look like they would work.
Therefore, with the help of my favorite facebook group, "Backyard Ducks (Meat, Eggs & Pets)", some of my book references and the internets, here is a compilation of bird diapers that i have been made aware. I have separated them into two groups: Ready Made and DIY
Make sure to follow the site's instructions for sizing of your bird.
Purchase ready made
Party Fowl Pets. They make diaper with harnesses and shoes. They have open tail and closed tail models. Indian Runners are recommended size C5. They have a variety of colors. They run $40-50+ per unit.
Fashion my Feathers. They make diaper harnesses, bow ties, tutus and other costumes. They are a fashion boutique for ducks. their site is not very easy to navigate and you have to join a closed facebook group in order to see what they have in stock and maybe prices. More details will be provided once I am accepted to the group and have a chance to look around.
Avian Fashions. They have diapers with harnesses for Ducks, Geese, Chickens, Parrots and even Pigeons. They also carry hats and toys for birds. Their standard harness diaper runs $35. This is also related to The Goose's Mother diaper/harness. I'm adding this link because it's useful for measuring and training the bird to accept the apparel.
Crazy K Farms Hen Holster. Diapers made to order for Chickens. It does appear it would be fairly easy to add some harness hardware to the diaper. They have several colors, 3 sizes and an instructional video. Theirs runs $30 a unit. Another related link : Hen Saver's Hen Holsters. They also carry crop bras, chicken booties and fowl exercise obstacle courses they dub gyms.
Sew Sammi. Their diapers run at $15 for duckling and $40 for adults. They also do costumes, including batman and superman. Diaper care kits, harnesses, quilts for furniture or car (felt), service animal vests are also among the products they offer. Another related link from the Backyard Chicken group where the seller adds bow ties, tutus, measurements and color options to the mix in 2016.
DivaVonTease's Etsy shop. Hand made, to order, water resistant lining duck diapers run about $25 each and are available in 3 sizes and various patterns, but appears to be just the one model, making the choice a bit easier. They recommend using a puppy pad or human diaper to minimize leaks. They are out of Colorado. This seller developed their design out of personal need for their own house duck(s).

Louise's Country Closet on Etsy. This shop features chicken diapers running at $15 each. They also carry chicken saddles also known as chicken aprons to protect their feathers during mating sessions. I found particularly interesting the machine embroidered lace ornaments, some with the obvious Christmas theme, some christian themed and of course, some chicken themed. They also have made in USA aluminum signs... My favorite: "rock out with your flock out"
KalindaZ's Etsy Shop. Currently taking a break. She was selling diapers dubbed the Dino Ducky Diaper with absorbent pads that look fairly functional. She also has a video on youtube to show you how to measure your duck and another one on how to put her model diaper on the duck. Even though she doesn't have any products for sale at this time, I thought this would be a great example to include here.
Pamper Your Poultry on Etsy. This shop features chicken diapers available in extra small, small, medium and large starting at $15. They also carry saddles/aprons and costume dresses. Their unique item is a Peep Pouch for clean and safe handling of baby chicks.
Walmart. Apparently Walmart has a chicken/duck diaper. The order page only has one of the measurements, i'm assuming length not width. Available in Medium or Small in random colors for less than $10 per unit. New Chic has the same exact picture selling at $14.
Ebay. Ebay has alot of people selling the same type of diaper. This is very similar to the Walmart/New Chick version. They go for under $12 there. Wish.com also has the same ones under $7. This is where I got my first diaper. I got the smallest model because I wanted to use it on a duckling. Things didn't work out cause it was still too big for his 2-3 weeks of age at the time. It also took forever to get here because it came all the way from China.
DIY Instructions
Backyard Chickens Forum : Duckling Sock Diaper Post. Made of a sock and shoe laces. No sowing required, just need a decent pair of scissors or a fabric cutter.
Steff J has a 15 minute video where the first 5 minutes is an intro and then she shows how she puts together 4 duck diapers for her disabled duck "Babette". Her diapers are then outfitted with a human diaper. Her video doesn't go thru the step by step instructions, but if you have some sowing experience, you can likely figure it out. This lady does love her bling but the result is pretty nice.
Surgical Mask or Flue Mask is an option that has been suggested in the facebook group. The type with the adjustable straps and in the biggest size available for the size of a standard duck or chicken.