One of the most dangerous birds in the world - I'm not kidding here - is the African spur-winged goose Plectropterus gambensis [the adjacent painting - from wikipedia - is by Louis A. Fuertes, one of the greatest zoological artists of all time]. Weighing as much as 7 kg, this formidable bird (not a goose in the strict sense, but a member of the shelduck/sheldgoose clade Tadorninae*) bears sharp spurs on its wrists. The birds use these in attacking both other spur-winged geese, and other waterfowl (at least in captivity: a captive individual kept at Slimbridge maintained a territory on top of a small hill. Waterfowl of other species would sometimes climb the hill, get attacked, and die from their injuries). It's quite plausibly dangerous to people, but I can't find any explicit statements on that [in the stuffed specimen shown below - from Scientific-web - the wing spur is visible at the wrist joint].
* Its superficial similarity to the Australasian Magpie-goose Anseranas semipalmata meant that it was once classified alongside this species. It was also thought intermediate between screamers and anatids during the 1860s, and affinities with true geese have been suggested at times.
Anyway... as if this isn't bad enough, members of this species can sometimes be poisonous. But I don't mean that they can inject venom with their wing-spurs, or anything like that. Rather, some populations (those in the Gambia) feed on a poisonous beetle (specifically, a member of the blister beetle group (Meloidae)), and then sequester the beetle's poison into their own tissues (Bartram & Boland 2001). Blister beetles are well known for producing the toxin cantharidin, small amounts of which (as little as 10 milligrams) cause death in humans. The effect of cantharidin on the urinary tract (it results in swelling of the genitalia) means that people have been using it as an aphrodisiac for centuries; the Spanish fly Lytta vesicatori is a blister beetle. So the result of blister beetle ingestion by spur-winged geese is that their flesh is toxic. Eating one can - apparently - result in death (Wanless 2001) [Plectropterus in flight shown below].
While the poisonous tissues of several passerines - notably the various pitohuis, the Ifrita Ifrita coronata and the Rufous shrike-thrush Colluricincla megarhyncha of New Guinea - is now quite well known (this was covered on Tet Zoo back in 2008), they aren't alone and several other birds are also known to sequester toxins from various animal and/or plant prey. Quail Coturnix coturnix are known to be toxic when on migration, but only certain populations are, and only on part of their migratory journey (e.g., those flying from west Africa to Europe are toxic; those going from eastern Africa to Europe aren't toxic, but are when they return to Africa in the Autumn). Being poisoned by quail even has a name (coturnism): there are accounts of it in the Bible, and it was so common in the Roman Empire that the eating of quails was banned in the 1st century (Bartram & Boland 2001).
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