When droppings collect at the vent there could be a few things contributing to it, perhaps one of the most common being an egg needing to pass. Quite a few owners are shocked after many years believing they have a male bird and finding that not only is it a girl, but it's in trouble. When an egg is stuck (egg binding) it's an emergency situation that needs veterinary intervention quickly.
Giving the bird a soaking in a shallow pan of warm water will remove the droppings and if there's an egg bound, may relax the muscles enough to allow safe passage.
This is also a soothing option for males suffering pasting for whatever reason.
Another possible cause of vent pasting would be urate crystallizations which are not uncommon in birds on a largely seed diet.
Further causes would be impaction from eating grit or other non-food items.
In any case, as you know, it's going to be necessary to have a hands on vet evaluation done to get to the bottom of the issue.
What you can do while securing a vet to see your companion is supportive care.
Most birds will need a heat source to maintain body heat while you're getting their medical treatment lined up or while you're on your way to see the vet with them.
If perching is a problem, lower the perch to just a couple inches above the floor of the cage so falling doesn't injure them. You might also want to remove the perch completely and layer newspapers on the bottom or put a tee shirt there. We use T-shirts because bath towels tend to have looped surfaces that can entangle little toenails.
Putting a heat source into the cage may be necessary since a sick or distressed bird may lose body heat. I prefer a non electric source and use rice socks.
Use a thick, clean sock and fill it ¾ with plain, raw white rice. Knot the end and microwave it for about 1 ½ minutes. Shake it afterwards to distribute the heat and be sure it's not too hot.
You can layer a thick towel on one side of the cage, secure with clothespins out of the reach of the bird's beak - then clip a heating pad over the towel and set on low. Check often to be sure it's not overheating and that the bird isn't gnawing through. A side attachment like this will allow the bird to move closer or away as needed.
If the bird is bottom-bound, install a heating pad under just a portion of the base, again, set on low.
The rice sock option is far safer and more efficient though.
Cover the cage with a thick blanket, leaving all or part of the front door uncovered for better air circulation, to help keep the bird calm by being able to see out and of course so you can check on it regularly just by peeking in. The covering also helps hold some of the heat inside.
If your bird will drink and eat on their own, excellent. If not, have an eyedropper ready to administer a few drops of plain water, or better yet, children's Pedialyte every 20-30 minutes. Put the dropper gently inside the beak and let the drops fall into the bottom beak under the tongue rather than trying to get into the back of the throat. We don't want to chance the bird inhaling the fluid and developing pneumonia.
Another feeding option is to offer ½ spoon of all natural, organic baby food (squash, yams, sweet potatoes, mixed vegetables) which many birds take readily; also try some pabulum or baby rice cereal and a few licks of natural (no artificial anything) yogurt.
If your bird develops distress from overheating: Gently spritz a light mist of cool water without frightening them and focus on their feet. Pouring a gentle stream of cool water on their feet may also be helpful.
http://www.exoticpetvet.net/avian/heat.html (details on overheating)
These are just temporary supportive measures to keep your bird alive while you get professional, hands on care. These measures will not cure your bird.
Don't mistake what looks like recovery to be a real recovery. It is very common for a bird to regain enough strength to start hiding their illness again, but what's happening is that it's progressing and by the time you see symptoms again, it will be much worse or too late.
Find an avian vet near you http://aav.org/vet-lookup and
http://veccs.org/hospital_directory.php
These days, with birds growing fast in popularity as in home companions, many DVM's are quite experienced and able to see and treat many birds. If you have a pet store that sells birds or know of any bird breeders - ask them who they use for their bird care.
Good luck and keep up the excellent observations. You probably saved his life by catching this early.
Certified Avian Specialist
Cert. Avian Specialist; Int. Assoc.Animal Behavior Consult; Pet Ind. Joint Advisory Council; author