That's what stood out to me too. That is an absolutely enormous image, easily twice the width of the viewport on a 1080p display, of which there are zero examples in the handheld world.
Even loading it in situ and having it scroll across the viewport will be a big commitment in storage; in essence, to make the image shuffle around, it has to be loaded completely first, then shifted, which requires a VRAM commitment of 3900 x 250 pixels - 975,000 KB RAM - times the 24-bit information save for the colors on the pixels, which Photoshop tells me requires nearly 3 MB to display. That's just the BirdShuffleSprite.
Portable devices are not dedicated gaming systems with a massive GPU that do things like that without breaking a sweat; and they are coded to force apps to terminate when they begin to invade active system space. If a user has several high priority apps running in the background (and most do, without realizing it), such as mail, calendars, and schedulers, well, the system might well have to kill something, and it's likely to shoot down the lower priority targets first.
== Meta discussion ==
Try to be conservative in what you expect your users' machines to be able to handle; never assume anyone on the home-user level is running with a 27" screen, 8 GB VRAM, a paired quad-core processor, and 32 GB RAM; and at the very least, remember that many handheld users are charged for bandwidth. Don't push more data than is strictly and absolutely necessary. A 3200px-wide image is probably not necessary. Your BirdShuffleSprite, RumpShaker, and Snuggle images would make a lot more sense as an animated GIF than a wide stripe that runs back and forth on the screen.