Dealing with heat stress

Budgies are from one of the hottest countries on the planet. Therefore you would expect that they could survive extremes of temperature, and they do.
 
I have noticed that a lot of breeders loose birds in weather that I would describe as moderately hot. My region has temperatures that regularly climb into the high 40's the top temp last year was 48 degrees C. The birds survive and actually breed fine without the need for air conditioning etc.

If you are loosing birds I would check a few things:-

1. Make sure you have nothing in the water like vitamins, medication or anything else. Only use clean fresh water. Hot weather increases the water intake and if you have fortified water firstly you could be poisoning and making your birds ill, or if they don't like the taste of the water they will only drink minimal amounts which may not be enough for survival. 
2. Have open drinkers where possible to encourage evaporation. Open vessels can be up to 10 degrees cooler than enclosed drinkers ( because of evaporation). Enclosed drinkers/bottles will be at the ambient temperature of the aviary. I have open water dishes as well as the enclosed drinkers in every breeding cage and all the aviaries.
3. Don't try and cool the water with Ice or anything, encourage evaporation. On hot days you will see the birds sitting above the open dishes to catch the cooling updraught.
4. Ventilation is also good to promote evaporation and its cooling effects.
5. Only enter the bird enclosures early in the morning or late in the evening when it is a little cooler, this is much less stressful on the birds. Replenish the water with fresh water and leave the birds to work out the most comfortable place for themselves. They are smarter than you think, they have been about for millions of years so they know what they need to do to survive. STAY AWAY
6. Make sure your birds have access to the lowest part of the enclosure. They will sit on the floor on the hottest of days. Hot air rises pulling in cooler air down low. 
7. Make sure you have a strong line of birds, if you get you stock from aviaries that 'molly coddle' their birds with air conditioning etc. you can end up with a soft line of birds that will not cope with normal conditions.

 This is by no means an exhaustive list of things that will help your birds cope with adverse weather situations. Fresh water, Evaporation and the resultant airflow and leaving the birds alone is probably all that most whom are having problems will need to address.
Good Luck and Stay safe.
All the best for 2020.