Little fur coats don't seem eqipped for hot weather, bless them. I'm sure in The Wild, they'd find some nice cool soil to lounge on.
But , in domestic situations, they are confined to a hutch, a run, a cage. Wooden hutches absorb heat . They like their bedding to hide in and though deep hay is lovely in Winter, it cooks them in Summer.
So: ventilation -my lovely DH fixed two of their windows so that they can lift out of the frames but inside is lined with bars,wire mesh and fly mesh, covering all the bases. They have a clear tough plastic screen that covers the window so they can be protected from rain but still get fresh air (I secure it so it is at an angle from the window frame)
don't leave them near full sunlight
my Himalayan guinea-pig likes a dark cover (I have a couple of fitted sheets which slip over the run)
we've used those big flat chill packs (the smooth blue ones, about the size of a small magazine) wrapped in newspaper or an old ceramic floor tile with a layer of newspaper
2 litre empty soft drink bottles filled with water and frozen, tucked into their sleeping area
lots of fresh veg (mine don't drink water <<sigh>> ) cucumber, watermelon, salad leaves quickly rinsed and leave the water clinging
clean their bedding more frequently (ours are daily anyway, mucky pups) Look out for flies (Flystrike can kill) . We have mesh on the windows of our Pighouse and their garden hutch
We hang those Citronella blocks outside their house (out of their reach)
You can drape cold water rung out towels over their outdoor run to cool the air
I cut the hay bedding right down to just eating hay, and give them shredded card to sleep in, or if I have any old towels, the Pigs inherit them. (They like to sink their weary bodies into a folded up towel )
We let them have grazing time in the evening when its cooler, they are more active.................but so is Mr Fox, so we need to keep a check on them
Look up the symptoms of heat exhaustion - it can kill. If your small furry animal is heat exhausted - lying flat (not the cute little croissant shape) panting heavily, can go onto have fits. You need to cool them, wrap inwet towels, get their temperature stabilised and once they are cool (not before) a drink to rehydrate.
Check their bottoms, especially older, fatter animals (can't reach well to clean themselves) , if they have loose pooh . Magnet for maggots <<boak>>, they can hatch in hours and get to work.
Our piggies love Summer, even when they judgily flaunt their Real Fur (just to get my dissaproval) , it means extended grazing and larding about being wild. Then home at night for a good sleep after a good supper
I just got a huge run for my two bunnies and I am 100% sure bunny no. 1 is starting to make escape plans from the hutch-attached run to the big one on the lawn. He already looks at me with quite sad eyes that I am not allowing them back on it after 3 glorious days over the weekend.
But this stupid weather means the lawn is too wet. I think he tries to make himself waterproof by sitting outside in the rain instead of hiding in the dry and cosy hutch upstairs where his "wife" sensibly decided to withdraw to.
For warm weather: the hutch-run combo is on the patio so the stones are nice and cool-ish. Lots of water and going to the run helps. Bedding in the hutch is down to minimal amounts.
Mine are more likely to suffer heat exhaustion in the cooler, rainy weather. They live in the utility and the tumble dryer has been on a lot to deal with washing mountain! It's like a tropical rainforest in there. Scruffypig is sure he saw a toucan!