Birds eat all kinds of food items, some of which very much appeal to our own palettes, particularly things like fruits berries, nuts, corn, and maybe even fish, crabs, mollusks, and crustaceans. However, side from sushi lovers, most of us prefer these later types of food at at least a partly cooked format. Then there are those birds that eat things nearly everyone finds to be downright repulsive.
It's doubtable that you know even a few people who salivate over raw meat of any kind or have an appetite for insects or slimy invertebrates, let alone carrion. Sure there are lots of people in this word that eat road kill and other things firmly planted in the category of weird, but generally speaking we can chalk this up to cultural differences or isolated oddities of the world.
One thing that a few birds are known to eat that we humans simply do not consume, at least not as food, is wax. Wax in the naturally occurring and general sense, refers to a class of organic compounds that are insoluble in water, solid and breakable when cold, solid but malleable at ambient temperatures, and which melt into a low viscosity liquid at higher temperatures. Wax consistants of long-chain fatty acids and is very difficult for most organisms to digest. Aside from its limited appearance in things like chewing gum or for wrapping some types of cheeses, wax is just not something we eat, but rather something we have found all sorts of creative practical applications for. Birds can always be counted on to defy basic logic or provide exceptions to general rules, and eating wax is no exception.
There are actually several groups of birds that purposely eat and are able to metabolize wax. Many seabirds, for example, like petrels and auklets, indirectly derive energy from the wax found in the crustaceans they eat. Then there are a handful of terrestrial birds, like certain warbler and swallow species, that gorge themselves on waxy berries. The digestive tracts of these odd birds are characterized by higher concentrations of gall bladder secretions, greater concentrations of bile-salt in the intestines, and a relatively slower passage rate of lipids acquired than food items. There is also some evidence that these birds are kind of like ruminators, like cows, such that partly digested wax compounds somehow return to the gizzard from the small intestine for a second or third round of digestion.
Amazing as all that is, none of these birds are eating straight up wax, they are just kind of forced to consume it because it is an unavoidable part of the actual food items that they prefer. Enter the Honeyguides (Indicatoridae), a family of 17 species found only in Africa and classified in the same order as woodpeckers (Piciformes). Fairly unspectacular in appearance and basically about songbird size, these birds are mostly insectivorous, but they are famous for their curious behavior of eating the pure wax of honeycombs. Rathermore, these weird birds solicit the help of honey loving animals like honey badgers and even humans by calling their attention to the location of a beehive so their assistant will open the hive to take the honey and leave the waxy comb and bee larvae to the honeyguide .