Among believers, vaultgulls are said to possess golden feathers, as well as eyes of black crystal; then again, they are also said to have never before been seen, so such descriptions ought to be met with skepticism.
For these clever birds, all that is unseen is the sky; their wings slide cleanly through metal and stone as easily the wind. The only solid surface they know is the periphery of human vision, the greatest obstacle to their shimmering wings. The subtlest twitch of a single eye is enough to thrust them aside like a hurricane's gales.
These scavengers have proven to be of utmost nuisance to the wealthiest among humanity. Their fortunes are so great that they can only experience a small fraction of them at a time, and as such, they keep the rest hidden in dark, sealed chambers underground. While this is an effective defense against thieves of the same species, it is ultimately ineffective against vaultgulls, whose feasts are actually facilitated by such precautions. These birds do not care for, nor do they recognize the differences between forms of human wastefulness; it just so happens that buried treasure is the easiest form for them to prey upon. As soon as they find an opportunity, they fill their tiny beaks with precious metals, gemstones, and anything else they can find buried within their liminal domain.
Most financiers dismiss the notion of vaultgulls as mere superstition, similar in nature to belief in gremlins; for them, such things are little more than creative excuses for negligent accounting. They often cite new innovations in surveillance, from CCTV cameras to one-way mirrors, as evidence of the absurdity of such an explanation of lost assets. What they fail to understand is that such technology does not inhibit these creatures at all, and only serves to outline how vast the unseen world they occupy is at any given moment.