One critique... Black Vultures do not actually have a well developed sense of smell compared to other a couple other species New World Vultures (Cathartiformes). At least Yellow-headed Vultures and Turkey Vultures are known to have well-developed senses of smell.
I did find a citation for "leading them to food in the first place— due to their superior sense of smell" on an ornithological note on Birds of the World, which cites this 2009 paper. However, this paper is mostly about reporting instances of allopreening (yay! We love it!), and only mentions the food-finding capabilities of Black Vultures in the conclusion as one possible explanation of why Caracaras may roost with Black Vultures:
"(3) Opportunism by crested caracaras
Cathartidae is one of the few bird families in which the representatives use chemical odors find food location, as they use their strong sense of smell to find carrion kilometers away (Owre & Northington 1961; Houston 1986; McShea et al. 2000). therefore, vultures are, at least in theory, much more efficient at carrion location than opportunistic species which have no records of such ability, such as the crested caracara. In that sense, the caracaras gain advantages in food detection by grouping up with black vultures."
ALL THREE OF THE STUDIES THEY CITE ARE ABOUT TURKEY VULTURES!!! Not Black Vultures.
Houston, D.C. 1986. Scavenging efficiency of Turkey vultures in Tropical forests. The Condor 86: 318-323.
McShea, W.J., E.G. Reese, T.W. Small & P.J. Weldon. An experiment on the ability of free-ranging turkey vultures (Cathartes aura) to locate carrion by chemical cues. Chemoecology 10: 49-50.
Owre, O.T. & P.O. Nothington 1961. Indication of the Sense of Smell in the Turkey Vulture, Cathartes aura (Linnaeus), from Feeding tests. American Midland Naturalist. 66: 200-205.
So they are just extrapolating wildly based on what is known about other Vulture species. I don't know whether there was established research yet about Black Vultures sense of smell or lack there of in 2009, and have already spent too much time on this, so not sure whether to blame the authors or not for this.
Black Vultures likely do have some sense of smell, but it is most useful for finding obscured food at close distances. They do not react to carrion smells at 40-50 meters away. Also it looks like Caracaras probably also have some sense of smell.
To be clear, I love the information about allopreening and it's an excellent photo!!! I just also really love accurate information about Raptors. This is an interesting case since Birds of the World is ostensibly reliable and did cite a scientific paper, so I only caught it because I have read other papers and information on vulture olfaction. Interestingly, this isn't mentioned in the full article (Black Vulture Birds of the World Page - linked but paywalled... sorry)
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