No, it doesn't work like that. Red Squirrels are smaller, lighter and more arboreal than Greys. Pine Martens hunt mostly on the ground - where the Greys mostly forage - and in any case can't get out on the thin twigs that afford the Reds refuge. Hence you don't get the same result.
Cheers
John
I think this is not the whole picture. In the UK, where Grey is abundant and Red not, Pine Martens are clearly targeting the available Grey Squirrel and where both occur, they still target Grey as it is easier to catch as John explains and is a larger meal.
However, if Grey were to be eliminated from the UK and Reds again more abundant, it is likely Red Squirrels would become far more important in the diet of Pine Marten. Red Squirrels getting out onto the thinner branches is fine during the day, but Red Squirrels are diurnal, Pine Martens largely nocturnal - they catch them during the night.
Some studies in Europe have shown that Red Squirrels can account for over half the diet of Pine Martens. Here in Lithuania, there are no Grey Squirrels, but Red Squirrel is distributed across the entire country. However, considering the excellent and abundant habitat, the reality is that Red Squirrels are remarkably thin on the ground, they occur at very low densities. I was always puzzled by this and actually asked a mammal researcher why ...Pine Martens.
Lithuania has a very high density of Pine Martens (I see far more of these than Red Squirrels) and it is likely that it is this that keeps Red Squirrel numbers low. As a simple example, if I put a trail cam on my land, I get Pine Martens every night. By contrast, I see a Red Squirrel on my land once or twice a year if I am lucky, occasionally more often. On the rare occasion that a Red Squirrel starts to use my peanut feeders, it invariably suddenly disappears after a period.
