I've heard of "Mexican Buzzards" as well. As with coyotes, it does happen but not as frequent as described. I suspect they're more interested in the afterbirth, and any predation is rare/opportunistic.
"Black vultures (Coragyps atratus) are often present near calving sites, and under this situation they may play a positive role by removing animal carcasses and afterbirth or a negative role by attacking neonate calves or disturbing cow-calf behaviours following parturition. Cow-calf behaviour was recorded over a 4-year study period from a total of 300 births involving 200 Nellore, 54 Guzerat, 20 Gyr and 26 Caracu cows. The calving site in relation to the location of the herd, considering cow-calf pairs within, close or distant to the herd, the presence of vultures and the behaviour of cows and calves were recorded instantaneously, at 5-min interval. On average, vultures were present at 80% of the calving sites. The frequency of vultures present at calving sites was dependent on the years for the Nellore herd, increasing from 1998 to 2003. When vultures were present, the time that the cow was in contact with its calf decreased, and the percentage of time that the cow was standing still increased. Vultures were observed pecking cows and their neonates during 34.1% of all recordings. However, in only two cases pecking injuries were actually observed on calves that were noted to be very weak. The preliminary results suggest that although black vultures cannot be characterized as a predator of neonate calves, they sometimes attack neonate calves and their presence near the calving sites alter the behaviours of cows and calves."
From: okbirds <OKBIRDS...> on behalf of Steve Schafer <steve...>
Sent: Saturday, June 8, 2019 2:35 PM
Subject: Re: [OKBIRDS] Black Vulturs
Yes, Black Vultures are known to attack newborn livestock: calves, lambs, etc. It's uncommon, but it does occur.
From: okbirds <OKBIRDS...> on behalf of Bob and Nancy <blnllaval...>
Sent: Saturday, June 8, 2019 3:07 PM
Subject: [OKBIRDS] Black Vulturs
I drink coffee with a bunch of guys every morning, composed of ranchers, and chicken farmers and others. I heard something yesterday I have never head before. One of the ranchers was cussing Mexican Buzzards. I asked him what he was talking about. He described Black Vultures. He said they are killing some of his calf's. He described an action by the Vultures that he has observed more than once. The vultures swoop down on a live new calf laying on the ground and peck the eyes out if they catch the mother too far away. The calf of course starves to death and the vultures feast. Others around the table agreed. They say the BVs are new to the area at least in large numbers. I see a few every summer but Iím not really out on the ranches. Has anyone heard of this habit?
20367 Pine Mtn. LP
Heavener, OK 74937