Over the years, it's become increasingly obvious that birds are in fact, not living. Instead, they are artificial remote spy tools. When the Patriot Act was signed on October 26th, 2001, it gave the government the right to gather intelligence on the population in the name of anti-terrorism. This was a move specifically made to enable the unleashing of the artificial birds, in development since the court case Barrett v. State of New York, which enabled the government control of wildlife, including birds. However, it is very possible that prototype birds were tested before the 2000s.

In the winter of 2001, the NSA unleashed a bioweapon into the bird population, killing up to 99.999% of all birds, and continuing to dissolve their bodies after death. Of course, this wasn't noticed right away, as all the birds were in the south for the winter.

The next spring, instead of birds migrating back up north, the bird drones were released. These birds were outfitted with high-definition color cameras, sensitive microphones, speakers for realistic bird tweeting, and realistic animatronic bodies, all while still being able to last over a full year on a single lithium ion battery. It's fairly clear now why it took them nearly a century of development.

Since then, the birds have been on a consistent schedule, spy during the warmer months, and fly "south" to a government facility, where they are updated, recharged, and/or repaired.

So what if I see a bird during the wintertime, government shutdown, in a Faraday cage, etc. As I mentioned before, the bioweapon killed 99.999% of all birds. It is likely some bird have developed mutations that made them resistant to the bioweapon, and survived the operation. These birds have may have continued to reproduce since then, and the total population is unknown. It is always best to stay vigilant and assume all birds are drones. This also explains any bird carcasses you see with a lack of electronic looking parts. Another explanation could be a malfunction, caused by damage, or the loss of connection to the bird. If the bird malfunctions, it may not be able to return during the winter to be refitted. Some high-level birds have been reported to have false meat structure inside, in the case that they are killed on duty.

So what if it fails to the point where the bird cannot function at all? The birds are outfitted with a microscopic canister of exotic matter. The bird encloses a neutrino which encompasses some of the properties of naked singularity, which itself is impossible in the real world, as this reaction would be impossible under loop quantum gravity. When homeostasis can no longer be mantained, due the the lack of air cooling from not being able to fly, the neutrino is ticked off, releasing near-zero pressure which breaks down the Isotope-Ω surrounding the canister. Isotope-Ω is the name given to the publicly unknown element with opposite properties of plutonium, reacting with negative (relative) pressure, radiating photons, and is liquid at even extremely cold tempteratures. The Isotope-Ω is completely broken down into photons, which penetrate the canister with the exotic matter, and heat up the bird to unprecedented levels. All parts of the bird are evaporated within a femtosecond. As you know, heat rises, and the evaporated bird is no exception. With the extreme heat levels, the gasses reach the arctic very fast. This is what forms the northern lights, it's the evaporated exotic matter floating around the atmosphere. On the other hand, this extreme heat also causes global warming. If you look at the statisics, the latitudes affected the most by global warming are all in the arctic, the only location this matter travels while still heated.

Other modifications to the bird drones over the years, taking advantage of strange behaviors. Birds can recharge easily outside of winter months by sitting on power lines, going up one leg and down the other, similar to how christmas lights get power. This behavior is now discouraged in bird programming due to birds malfunctioning while on the power line, blocking power through its body, and causing power outages, also similar to christmas lights.