Cant recall that recent a research, but if its work I am thinking of from Kruger, - it was Paul Funston that was most recent - His most important finding was that male lions spent a proportionally greater % time away from pride females, and thus did their own hunting and not scavenged as much from pride females. The major influence was thought to be the wooded ecosystems (among other things)- there is whole long shpiel and cannot go in depth - but have that reference:
Funston etal. 1998. Hunting by male lions: ecological influences and socio-ecological implications. Anim. Behav. 56: 1333-1345.
In Savuti, Sue Cooper (i think was her name, 1991) figured that the ratio of hyenas : lions must exceed 4 : 1 to rid lions of 20 % of their food - she was in Savuti, and the problem there was that hyenas were scavenging significantly from lions - (hunting concessions adj. had removed large trophy pride males appreciably). Kruger hyenas never exceed 3:1 relative to the group of lions at a kill (Funston above)
The numbers of predators in a group will determine their ability to scavenge from another. Kruger hyenas supposedly scavenge 50 % of food procured (Mills etc.), and they hunt more in E Africa (Ngorongo & Sereng.), where bigger groups enable better hunting and scavenging abilities from lions too.
There are lots of studies done, and many were done ages ago, on that issue. I have dug older stuff up, but maybe you are referring to something newer that am unaware of. let me know.
WTM's post somewhere here got me thinking about this and I thought I'd let you into something I hear more and more by people in the wildlife field.
Hyena's have always been labelled as scavengers and lions not. Recent research into this has discovered that while hyenas do scavenge they are also prolofic hunters and ,wait for this, scavenge less than lions. Males lions are incredible opportunists and being lazy are particularly prone to scavenging. I recently read somewhere where this was again confirmed. I'm almost sure it had something to do with a study in Kruger but I could be wrong. I will try and find it and post a referance here.
In the meantime maybe KNP Representitive can offer us more insight into this.