I understand both sides to this issue, I have heard from several people that a phobia of birds is a very common issue, no doubt related to my favorite director of all time, Sir Alfred Hitchcock...."It's the end of the world!" So I understand their issue, but I agree that it is very silly not to just tell you about it. I understand not wanting to offend you, but honestly I tend to think that they may not have told you partly because they did not want to upset or offend you, and partly because he is probably very embarrassed about having an irrational fear of birds. As you said, he's 6'5 and a big, tough man, so I'm sure he's not very proud of being afraid of little harmless birds.
I can relate on both sides of this issue. First off, my only true phobia is of insects and spiders. And I mean it's an innate, serious, deep-seated, psychological fear of ANY insect or arachnid. Even a single little ant or a "beautiful" (yeah right) butterfly freaks me right out, puts the fear of God in me, and sends me running for the hills. I can't get far enough away from whatever it is, and god forbid I'm stuck in a corner or somewhere that I can't escape from without going past the insect, because this psychosomatic thing happens and I end up doing dangerous things to get away. Once I was sitting in the showroom at work, we had this huge half-moon shaped front desk that was probably 5 and a half feet tall at it's highest front ledge that customers would walk up to, and I was sitting in a chair behind the desk, the desktop we used that was behind the ledge was probably 3 feet tall. A co-worker was sitting beside me, but at the opening of the desk, so I was crammed in the back of it. All of a sudden he yelled that there was a huge millipede crawling towards us across the floor, one of those ones with hair! I leaned around him, saw it coming towards us, and I literally elevated out of my chair, one foot on the desk platform, the next foot on top of the higher ledge, and jumped off onto the floor in front of the desk, and right out the door to the parking lot...I was told it looked like a Bruce Lee move. I wasn't even conscious of doing it. So if his fear of birds is one of these types of irrational fears that you can't explain then he probably is embarrassed about it...(at least insects are ugly, creepy, nasty, scary looking things, I can rationalize this much more than being scared of adorable little cockatiels, lol).
My aunt (my mom's brother's wife) has a horrible fear of dogs. All dogs, doesn't matter what breed, their size, etc. I guess she was attacked by her parent's dog when she was very young, like 5 years old, and she was injured pretty badly. So she had a horrible fear of any and all dogs, though they have always had cats and she loves them. When I was in high school my mom finally got me a dog after me begging for about a decade. We always had birds, she bred birds, but I wanted a dog. So I wanted a border collie, went to the local pet store who had puppies, and ended up falling in love with the sweetest little girl pug puppy, she was 8 weeks old and fit in the palm of my hand. I named her Rudy (I'm a HUGE Notre Dame fan). My grandmother would always have Sunday dinner once a month, we always had holidays at my grandparent's house, etc. I have 2 cousins, my aunt's daughters, that also dislike dogs. Well my uncle loves dogs, he and my mom grew up with lots of dogs, my pap bred hunting beagles. My grandmother and pap were too old to care for a dog anymore, though my grandmother loved them so, she still had English budgies, but she missed having a dog to hold and pet and take naps with, walk, etc. So when we got Rudy, literally the sweetest little dog I've ever known, and I know I'm biased but Rudy was the ultimate lap dog, my grandmother would watch her during the day while my mom and I were at school (she was an elementary art teacher). She loved Rudy so much that she always asked us to bring her for Sunday dinner and holidays. Well you've never seen anything until you see a grown woman in her 50's completely freak out and act just terrified of a little female pug that weighed 20 pounds soaking wet. This caused a massive issue between my mom, my grandmother, my aunt, and my uncle. I had nothing to do with it, thank God, and my cousins hated all dogs as well, so they had no problem chiming in about how they didn't bring their cat to Grandma's house, but it wasn't my mom or myself, it was my grandmother that insisted we bring Rudy to their house to every family function! My mom often said that we would just leave Rudy at home from now on, and she would say this in front of my aunt and uncle, but my grandmother insisted that we bring her, and that my aunt didn't have to be near her and she would just have to get over it...It was stressful. But my grandmother was elderly, she knew they would be moving out of their house into assisted living soon, and she wanted her Rudy pug there as much as possible... Eventually my uncle convinced my aunt to just ignore Rudy, and I would put Rudy in my grandparent's TV den and shut the door while we ate dinner. Oye.
So yes, I think this is a common issue, I haven't been confronted with it yet, but honestly if anyone that knows me were to come over to my house and be upset about my animals they should have known better before they ever even attempted to come over, after all I have 2 dogs (a 3-year-old female Australian Cattle Dog that is very well behaved and well trained and a male Shar Pei who just turned one year and is Satan or a close relative thereof), a green cheek conure, a Quaker parrot, a cockatiel, and a Senegal parrot, each of which have their huge cages in my living room/dining room along with a huge flight cage that my 7 budgies live in, and then a male bearded dragon who has a pretty large Exo Terra in my dining room next to the Senegal parrot's cage. And upstairs I have 7 breeder parakeets in another huge flight cage that can be separated into individual breeder cages. Even though I stopped breeding them I couldn't just get rid of them, they are not tame at all but they entertain me when I'm upstairs with them. That bedroom used to be my breeding room/nursery where they would live and where I would house the baby chicks I would hand-raise, feed them, it has a mini fridge that holds medications, supplements, Pedialyte, etc., an incubator, and several small brooders. So the only place in my house that people can escape the animals is my basement (my house is a 3-floor split-level, so all 3 floors are completely finished). My basement was used as an exercise room, a foyer type of room with a large wood stove, and then a laundry room and half-bathroom. But I actually am turning the exercise room into another living room so that people can not only get away from all the animals if need be, but the basement is actually the ground floor that is level with the driveway, and you can go in through the garage. So if my mother or stepfather can't get up stairs or whatever as they become elderly they can stay down there, we can watch movies, eat, there's a bathroom etc. I actually just installed 2 electric baseboard heaters and ran the electrical so it's toasty down there now, I never had it heated prior, only when I was exercising I might throw a few logs in the wood stove. So I guess I am prepared for anti-animal people now, I just shut the door to the upstairs and that's it.
If I were you (and this is just what I would do) and this had bothered me as much as it seems to have bothered you, I would just call your friends up and tell them that you were told that he has a phobia of birds and that is the reason that they no longer come over to your house. I'd tell them you're sorry but you had no idea what the problem was and that you really wish they had just told you about it in the first place, because you can just put the birds away in their cages and put them in another room or cover them up or something when they come over. Life is too short to at worst lose friends or at best badly strain your friendship, all because of a misunderstanding or something that can easily be remedied by talking the problem out. That's if you want to fix the friendship and get things back to the way they were. Now if you don't care about that relationship then it's obviously a whole other story, lol...And of course if it's a situation where he can't even be in the same house as birds are in, like if just knowing that your birds are in a different room or hearing them totally freaks him out and he can't be in the same house as a bird at all, and the only way they will come back over to your home is if you get rid of the birds, then obviously that won't work and you'll have to either end the friendship completely or only see them at their house or out somewhere else. (I'm almost this bad with my insect phobia, I have a good friend who's daughter has a "pet" Mexican Hissing Cockroach in a 10-gallon aquarium in her room and I really can't be in her house, all I think about is it getting loose or her walking out into the living room with it on her shoulder).
It's a tough situation, but for me the bottom line would be how important the friendship was to me. Yes it was very silly and petty of them not to just tell you, but that can't be changed now, so if you want things back the way they were you'll have to make the first move and get this out in the open to see what they're thinking.
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