Dear Ilian, fortunately you understand very well the difference of roadkill impact on a small and tourism vocated mediterranean island, a hill territory as mine in Oltrepo' Pavese and the huge deserd of Baja California crossed maybe by only one poorly trafficked road...
Can I ask you what you think are the main causes of reptiles decline in Countries such as Italy? And mainly of snakes decline?
I could make you a list of the causes that in 40 years caused the decline and/or the total destruction of snakes around my house, where I live since 1972, but I can reassure you that at number 1 I will put roadkills.
If you want I will make a list.
You could ask me now: how can you be sure about this?
We have only two ways of proceeding, in order to understand the causes of snakes populations decline: direct observations and abstract reasoning. I use both.
By direct observation I can see that the only snakes found killed near my hometown (or in Cres) ar killed by cars. In particular rarer cases (but not THAT rare) they are killed directly and voluntarily by people.
And I can clearly see in the woods and fields the every year harder signs of wildboar presence: stones upraised and vaste zones of wood earth excavated.
I know from the books and science and literature that wild boars eat practically every organic thing that they find.
So, with reasoning, I can argue that they will eat a snake or a snake egg clutch if they will find them. And why they won't find them if they constantly make the deep sings I see with my eyes?
I think that these 2 are the main reasons of snakes populations decline in my region and on Cres. Or, better said: the two main reasons that have moved the delicate balance of snakes surviving (which functioned rather well till the sixties and seventies) towards a snakes more or less slow decline.
And, please... you cannot compare "road kills" with a sort of "natural predation"...
A natural predation has taken thousands or millions of years to reach a "steady state": road traffic is exponentially grown in few tens of years (I would exactly say from the 60-70s, when each family began to possess a car).
And a natural predation as the one by Circaetus gallicus has certainly more selectivity than roadkills, in which every snake that crosses a road or bask over it is killed without distinctions: newborn snakes, healthy adults, huge, small and medium sized specimens are killed by road traffic in matter of seconds in a same unnatural way...
And again, even if road traffic in Cres had the same selectivity of maybe 5 Circaetus gallicus couples, it will have anyway a sommatory effect with the existing natural predators (and the new less natural ones like introduced wildboars!), and not a replacement role only...
P.S. I have at least 3 books about Circaetus gallicus at home. They "never" predate newborn snakes! One of the main roadkill-victims on Cres are newborn totally healthy quatuorlineata and situla (pers. observations). Is this a natural way of selecting snakes?