disease, cures , and prevention
Fortunately this is not a big issue with captive migratory waterfowl. If keep fresh food, clean water, and a clean aviary, most all your waterfowl will stay strong as rocks.
There are a few diseases that can effect them, most are bacterial, mold, or rat induced.
As to Travis' question about botulism in the wild, I am assuming the puddle ducks are more effected than the divers due to their dabbling in the mud and eating more of the bacteria /toxins that cause it, where as the divers generally stay out in the open areas of the lake and dabble in mud much less.
Well cover it first
Botulism is fairly rare in clean aviaries. The problem lies in stagnate water full of decaying plant and animal material, especially in the heat of summer. The bacteria (clostridia) that consume this waste release a toxin, the toxin is the problem. It will cause a loss of motor skills/control in their legs, neck and wings.
The only cure I have ever heard of is one of those old timer remedies, put 1 tablespoon full of Epsom salt in a cup or so of water and force them to drink it. Before any treatment will work though, the contamination must be cleaned up and bleached.
Best bet is to keep the ponds clean and just avoid it as dirt pond water will contain tons of different bacterias, none of which are good to start with.
Moldy feed
This can cause all types of fungal problems if they eat it. NEVER feed old or moldy food to your birds, clean up any uneaten food in the aviary as with the damp conditions it will mold over very quick, this is easy to avoid, just dont feed it to them
Coccidiosis.
This isnt too big of a problem for ducks, geese yes, not ducks though, but they can get it. First you must remove the contaminated birds as their droppings will continue to effect the others if you dont, treat them in a quarantine facility.
It is characterised by watery dropping, turning to bloody ones, then tarry ones. If not caught early, there is no help for them. A sulfur based med is the only cure, and mortality is still 75% or better even when caught early. If not discovered til it's tary, there's not much hope. Again, due to the nature of ducks, they dont tend to get this very often, grazing on pooped on grasses are the main transfer points of this disease, as contaminated poop from one bird has to be eaten by another for them to get it.
Pasteurella
I have never experienced this one myself. It is characterised by watery dropping that turn green over time. It is caused by a bacteria transfered to the my rats in the feed. If they get this, in addition to the green poo, they will have a loss of appetite, and increased water consumption. Unfortunately, this is one of those near totally fatal bacterial diseases, nothing much to do.
Avian Tuberculosis
This is another rat disease. It is commonly called GOING LIGHT, It is characterised by a bird looking totally normal, eating and drinking just fine, then one day you will notice it acting lethargic,and clumsy. Once you catch it you'll instantly see it is nothing but a breast bone with feathers around it. ALL POULTRY can get this, and there is no cure, 100% mortality. With both if these two diseases, keeping rats out of your feed is the only prevention. There are transmitted by their droppings and urine getting onto the feed, so keep those rats out.
Mites
Fortunately if given adequate exposure to water, most waterfowl dont have too much trouble with these. If you notice a bird with dry, brittle looking feathering, it could be mites though, or a clogged oil duct. In the event of mites, there are a large array of dust and powders available to treat them with, or Ivermectin will cure them of that too.
1/2 cc orally for big species 1/4 for teal and such. For the oil duct clog, check it, it's just above the tail on the lower back, if it looks red or swollen, take a warm cloth and message it, often times, just a little cleaning will open it right back up and the duck can take it from there. This isnt a problem once again if given adequate water and a clean environment.
Internal worms
Like all fowl, ducks can and will get intestinal worms,
Ivermectin will fix all of them and external parasites as well in all poultry. It should not be given during or just before breeding season though as it usually sterilizes them for a few weeks. dosing differs on size, age, and concentration of the produce. IT IS NOT WATER SOUABLE, despite what everyone says on forums. It should only be administered orally or as a drench. SafeGuard is also widely acceptable for poultry. It is safe to use during breeding, but doesnt get external parasites as well as Ivermectin. It is slightly water soluble, if they drink it quick it will still be in solution, if is sits for a few hours though, it will settle to the bottom of the water dish. It is best to give orally as well.
Wazine is water soluble and widely used but only kill round worms.
I always wormed my birds during pond drainage where they were only allowed water in the drinking bowls. Twice a year is fine, once in January or so, and again late summer.
Clogged nostrils
If you have ever watched ducks for long, you will notice that they often stick their bills under water suck and blow, this is just clearing their nostrils of dirt and debris and is of no concern to their health, again in nasty conditions or not exposed to adequate water, they can become clogged and need a helping hand to free the debris.
Respiratory diseases
There are lots of these, all bacterial in nature, if you notice them coffing, sneezing (not chirping and peeping like lots of them do) mucusy, swollen eyes, etc, get them on a strong broad spectrum antibiotic for respiratory disease, mycoplasma diseases are the most common and effect all poultry and are very contagious. Treatment for 3-7 days is recommended, if some still show signs, another treatment is recommended just to those birds if possible.
Again, for the most part, if we keep our feed fresh and clean, water fresh and clean, no green stagnate messy, and keep droppings raked up, waterfowl generally are one of the toughest birds you can keep and none of these problems will be an issue for you. Hope this helps some and will show you what to watch out for in your collection.