The e-mail Tony sent out inviting them to live in the Tower listed very few rules, but there was one that was bolded, underlined, and required you to acknowledge it before you could reply: ABSOLUTELY NO PETS OF ANY KIND.
This rule was reiterated as part of the welcome tour and also slipped into conversation frequently with varying degrees of subtlety the first few weeks they were all there.
(It probably would have worked too, if not for Natasha.)
Steve wasn't actually sure how long she had them before she came to movie night with a quartet of little blue and white parakeets on her shoulders.
Tony was clearly torn between making a joke about her being a Disney princess, reminding her about the rule, and wanting to keep his favorite body parts intact. One of the birds climbed up her hair like a ladder and stared him down like he was considering taking Tony’s eye out on principle and he just shut his mouth and walked away.
The birds made occasional appearances in public areas after that and they had the run of Natasha’s floor, perches in every room, some built right into the walls, others on ornate stands that were as much art as practical. The smallest one, a sweetheart with thin black bars on her wings and a chirp so high it was sometimes hard to hear, often came flying in to greet anyone who stepped off the elevator. She would land on a shoulder or head or—if offered—a finger, and chirp a greeting, then fly back to find Natasha and announce your arrival.
Steve found the biggest, a surly brute that made more of a growl than a chirp named Dmitriy, on the common floor by himself one day and tried to take him home. He lost a chunk of the skin between his thumb and finger for his efforts.
(Dmitriy was the reason Steve now had mag clamps for the shield on his right glove as well as his left.)
The next violation of the rule came after a battle with some AIM flunkies with a badly rebuilt Extremis knockoff. That was actually less fighting and more just containing them until they inevitably went boom. The chatter on comms was unusually sparse and not nearly as flippant, especially from Tony.
When Hulk showed up, after helping with search and rescue in an empty warehouse that had been a favorite spot of the local homeless population, with a tiny white kitten with soot smeared all over its long fur, Steve expected Tony to lay down the hard line and maybe even actually yell at the big green guy, but he said nothing.
The next time Steve went to see if Tony was hiding in Bruce’s lab to avoid his reminder that Phil needed their reports, he instead found a much cleaner kitten curled around a steaming mug of tea, tail covering the notebook Bruce was trying to write on.
Saṃsāra had full run of the Tower, though she rarely used it, more inclined to follow Bruce wherever he went, a tiny, fluffy, low-flying cloud at his heels. She and Dmitriy could not be left in the same room without supervision or there would be blood.
Thor came back from a trip to Asgard with a pair of what he SWORE were commonly kept house pets there, but Thor was never going to win at poker for a reason. So now there were two… Well, they looked like small dinosaurs. Meat-eater types, specifically.
Tony made a sort of despairing sound of resignation when one of them jumped up on the table and stole his pizza at dinner, but he also spent the better part of the weekend working on chew toys that could stand up to their teeth.
(Clint took Thor out to buy leashes and collars since even the Avengers couldn’t get away with having pets in violation of the city’s laws and came back with a bag full of stuff that Steve was pretty sure wasn’t for Blue and Reptar.)
Tony watched Clint leave for his jog a week later with a dog missing its left eye and his only question was whether Fury got himself turned into a dog somehow and Clint got stuck with pet-sitting duties.
Clint replied that the only way he would be assigned to pet-sit Fury as a dog was if literally everyone else in SHIELD had been killed, and that he and Lucky would be back in an hour if anyone wanted donuts.
(Tony was on the wrong side of his day, but he stayed awake until Clint got back and fed Lucky all of the bacon off of Steve’s plate.)
Steve considered getting a pet more than once since the rule had obviously been repealed, but he wasn’t sure “everyone else has one” was a good reason. Even if Sam tried to convince him it was while cutting raw chicken breast into strips for Redwing. The hawk fluffed its feathers and gave a screech of agreement, but that wasn’t enough to convince Steve.
Sam continued his attempts at persuasion as Redwing ate, citing the benefits with the other veterans he’d worked with.
“Animal companions are one of the most successful helps I’ve seen. And it’s not like I haven’t seen the baggies you keep in your pocket full of food you have no intention of eating. People quitting smoking, the elderly, and 5 year olds carry candy in their pockets, Steve. You’ve got Beggin’ Strips, dried salmon bites, and birdseed on you all. The. Time.”
When he was done, Redwing screeched at the ceiling and JARVIS opened the pane in the window Tony had installed as soon as Sam confirmed he was coming to New York to stay.
(Steve still wasn't sold on the idea.)
He did get a dog for Bucky, though, after he was released from SHIELD observation with a clean bill of health and a bunch of trackers and bugs sewn into all of the clothing they’d given him.
They threw the contents of the duffel into a series of dumpsters as they walked across town to a municipal building for their appointment. They came out an hour later with a black Sharpei-Brittany Spaniel mix who had more leg than brains but who had served honorably as a courthouse dog for five years before being retired.
Steve couldn’t deny Sam was right about how much General seemed to help Bucky, but that didn’t mean he was going to get one himself, no matter how many significant looks Sam gave him.
He got so used to seeing the two of them together, though, that the day Bucky walked into the common area without his shadow Steve sat up in concern from where he’d been sprawled on the couch watching a movie. Bucky waved it off and made a joke about being mentally sound enough to get food without an escort.
An hour later Steve cracked his eyes open to see General enter the room and jump up into Bucky’s lap like he wasn't 55 pounds of fur. Bucky patted his head and asked quietly if his mission was successful. General woofed softly and the noise from the kitchen eventually turned into Tony shuffling into the room with a plate.
He looked terrible, eyes still red and puffy and mouth set in a grim slash framed by lines even his goatee couldn’t hide. His hands were trembling and his shoulders looked like they had lead weights attached to them, but he just sat between Steve and Bucky and reached out to stroke General’s head when it landed on his thigh.
(He passed out not long after eating and didn’t wake up for the rest of the movie, his hand resting between furry black ears.)