Elderly cat meowing excessively

Our elderly 17-year-old kitty has been meowing excessively and it seems to have started after the death of our other old kitty (we still have two younger ones as well). You are probably thinking, "well of course!" - except for the fact that despite living together for about 12 years, these two cats never got used to each other, and hated each other's guts. However, they always slept together (keep your friends close and your enemies closer?). But ever since then he's been meowing and acting differently, sleeping in strange places, etc. Could it possibly be the death of the other cat that's causing this??? We've been to the vet and he does have chronic renal disease, but other than that, no physical reason for this behavior.

Has the vet ever tested for hyperthyroidism? that can cause excessive vocalisation and does tend to happen in conjunction with renal failure. It could also be looking for his friend, in which case lots of reassurance is needed, but I would consider hte medical reason first.

I would get the blood tests and he could be missing the other cat.

Just because they weren't best buds doesn't mean he isn't confused by his companion's disappearance. that he starts to enjoy living alone.

Dillon and Toby lived together for 15 years then Toby passed away and Dillon got louder and louder for the rest of his 5 years! He seemed to think that if I left the room I wasnt coming back so I stayed with him as much as possible, he had his cushion next to me on the settee and once I sat down, he quietened down. As he got older he slept more and more but when he was awake he wanted me there, although he was OK at nightime. If I needed to go out of the house for a couple of hours I would wait until after lunch as he slept from lunchtime to teatime.

He did have the test for hypothyroidism, diabetes, etc. I kind of thought that even though he and Jumbo did not get along (except for sleeping together) that he still misses him in some way. He is not an only cat though, we do have two younger cats but they seem to be too active for his comfort and he stays away from them. I have been giving him much more attention and stroking, etc. Thank you everyone for your replies.

I read once that you should ask your cats permission to talk to him and look him in the eye and tell him when his companion dies. I did this with Dillon (after all they had been together 15 years). We will never know if he understood but I felt he did. You have to ask for his permission first to talk to him though!!

It may be grieving, but that also may only be coincidental. My Bathsheba began vocalizing excessively when she was about 17 (lived to 20), and she had always been a very quiet cat. My vet said that it was hormonal shifts due to aging--in fact, when she was about 18, there were a few episodes in which she howled like a female in heat--again, the hormonal shifts caused this.

Coco meows for no reason all the time also and she is 16.5.
She had the hyper t test and it was ok.