So I actually used to work at the Post Office (when I was in my early 20s) and I was an express mail case worker. Essentially what that means is that whenever people had a problem with express mail (overnight and 2nd day mail, depending on origin/destination), someone would file a case and it was my problem to research it, solve it, or to conclude it lost, etc.

Anyway, virtually all animal shipping happens via Express Mail. So it became my problem to handle most cases involving animal shipping. I worked this job for about 2 years. I will tell you that every day animals die within the USPS. The vast majority die not because of the actual USPS, but because the people shipping the animals did it improperly.

Here's a short list of specific cases I remember:

- Someone shipped a baby alligator. They didn't mark it as live animal (because they thought it wasn't allowed) or ship it appropriately. The alligator chewed through a portion of the box by the time it arrived at the destination post office. A worker looked through the hole and discovered what they thought was a puppy, so they opened the box to save it and saw it was an exhausted alligator. Local animal control was called and the alligator wasn't able to be saved. Animal control disposed of the body. Alligators are actually very commonly shipped and are legal to ship, so if this person had done it correctly the animal would probably have survived.

- Rare butterflies were sent from Vietnam via international first class mail, when the box arrived it was flat and all the butterflies were dead. It got escalated to me because no one in first class mail knew how to handle animal cases. I remember this case in excruciating detail because the recipient continued to call and harass me for 3-4 months after this happened. This was a weird borderline case because it was international mail where the sending PO (in Vietnam) allows sending of these animals but local PO (in USA) didn't allow receiving of these animals. The guy was hellbent on getting reimbursed for non-insured first class mail. He claims he spent $10,000 on the butterflies. Since it wasn't insured we never researched the legitimacy of this amount, nor did he receive any compensation. Eventually Postal Inspectors were called just because of his continued harassment.

- Baby Chickens are commonly shipped. I don't remember any specific cases because in spring time I was handling 5-10 of these cases EVERY DAY. They also commonly do not survive, even when properly handled and shipped. So get your insurance if you order baby chicks. These are some of the easiest insurance reimbursements I have seen, they get approved faster than almost anything else in the USPS. It's insanely common.

- Someone shipped a salt water fish of some kind. The fish survived the transport but the recipient said the fish refused to eat because it was so traumatized from our shipping methods. So the fish went on a hunger strike and died a week or so later. They had spent $1,500 on the fish and wanted reimbursement. His reimbursement was denied.

- Someone shipped a fertilized Ostrich Egg. They packed it in bubble wrap and had some of those hand warmers inside that you use when skiing. When it was accepted by the recipient, they opened it and discovered the egg had cracked during shipment. Pretty standard boring case at first glance. But the reason I remember it is because the insurance claim was originally rejected because Ostrich was a non-indigenous fowl. Then the recipient sent back a 20 slide powerpoint to me that they created which proved that Ostriches are actually considered farmed-poultry (who knew?). So then I passed it through as approved but it was denied again because of improper packaging. Eggs have to be sent in "hatchery" packaging. I don't think that person ever got their insurance claim.

- Puppies. People actually try to ship puppies via USPS. Please do not do this ever. You will have Postal Inspectors called and they will fine you and charge you with a felony & animal abuse. Same goes for kittens, although for some reason puppies were more common than kittens. Both are big no-nos. Luckily these usually get caught early on at the origin post office or at the initial sorting facility, so many have been "saved" before they passed away. Animal Control retrieves the animals and they go to the pound/shelter. Either way Postal Inspectors get involved 100% of the time in these cases. So its a sure-fire way to get charged with a felony. I remember 2 cases where I was actually able to find lost puppies and save them. One time I spent close to 8 full hours tracking them down. They still go to animal control when they are found, they do not continue onto the recipient. The second time we found the lost puppies it was because the destination PO discovered them and called the police and the Postal Inspectors directly, but never updated the tracking. So the puppies were safe (I think one died in that case).

- Bees are very commonly shipped and they make it safely through the mail system 99% of the time. They actually pack them up and store them very well.

So what happens when a package gets lost? Well live-animals have the highest priority in the USPS' case management system. So even if I was behind on cases and working on cases that were submitted days ago, as soon as an live animal case comes in, it immediately moves to the next case above everything else. So they are handled promptly. As a case worker we usually actually picked up the phone to call sorting facilities when we were dealing with a lost animal as opposed to sending emails like usual for information. I'd say we tracked down around half of all lost animal claims. Some would get discovered "too late", and many would just get lost for good.

What happens when a deceased animal is discovered? If it was an approved animal then it would go to the recipient as usual, sometimes with a note. If the animal was unapproved (like a snake or turtle for example) then Postal Inspectors are called. If it was a larger animal or a mammal like a puppy or kitten, then animal control is usually called to handle the body.

Lastly, Ill mention insurance. The way USPS does insurance claims is a headache for everyone. We had a joke when I worked there that the goal was for people to give up on fighting for their insurance claim. Because that is what usually happened. Payouts take 6 months or so on average. There is a lot of back and forth and records need to be immaculate. Most people don't have any proof of what they shipped or the value of what they shipped. So claims were rarely approved.

Last I mentioned "Postal Inspectors". These are actual federal agents that oversee USPS claims. They are essentially federal police officers and they can arrest and charge you with felonies. They investigate all sorts of stuff, like mailing drugs, elaborate mail tampering schemes, and so forth. They also handled cases where extreme animal neglect occurs while shipping live animals. So keep that in mind when you ship a live animal against the rules posted on that site, because you can actually get a felony for it (like shipping dogs and stuff).

Edit: This was nearly 15 years ago, so some practices and rules might have changed since then.