Like all N.A. tree squirrel species, the N.A. Red Squirrel has a diet consumes more seed and nuts than any other food source. In captivity, their seasonal diet needs to be replaced by a proportional diet that means less nuts daily than they consume in the Fall where they gorge on nuts and seeds. like all tree squirrels. A difference in their diet from the larger mid to large sized tree squirrels of N.A. is that they have a strong bent towards consuming a greater proportion of animal sourced foods, much like that which the American flying squirrel species do as well. Their diet in the wild in this is varied, not just eating in season when nuts are not as yet available bird eggs and nestling birds, insects moths, larva and mature forms, as well.as well as other carrion and other animal sources for food. Also like the N.A. flying squirrel species, they possess a higher metabolic rate than that of the mid to larger N.A. tree squirrel species, which explains their greater need for animal protein. Rats in tis are much the same, opportunistic feeders with a likewise more varied wild diet than most of the larger tree squirrels species of N.A.
As a substitute for bird eggs and carrion etc. ; you can limitedly feed soft-boiled egg yolk and white chicken breast meat. Best to alternate the two on different days, keeping hte portions fed smaller than that of the wild for reason again that these animal sources are primarily spring to summer food sources.
For egg yolk, 1/4 Tsp. cooled and congealed. To make sure the egg yolk is sufficiently cooked, check the white to confirm it is fully cooked, that is hard; for then the yolk is sufficiently cooked. Egg yolk has about the same Ca:P ratio as that of English walnuts, that of 3.5:1 P:Ca. not a bad ratio for other in the wild diet.
The issue of too high phosphorus in the diet presents with a convenient need to provide vital nutrients time wise, rather than feed a homemade diet that is rather time intensive to support for having to measure each source fed over the course of a week on average. For to support a modified homemade recipe and still provide sufficient calcium to Phosphorus that needs to be for older juveniles at least 2:1 Ca:P whole diet ratio, and for adults higher. If you should choose to attempt this endeavor, I would direct you to Self Nutrition.com that uses the USDA Food Data base that you can use as a reference for various suitable foods for a captive diet for red squirrels. Keep in mind there would need to be sufficient Calcium level to offset the higher phosphorus protein sources in a homemade diet. Making up a recipe would be a more doable means to support a homemade diet should you desire to give it a try. You can reference the 1995 Rat Requirement listing for the RDA of rats which are in general also of a lesser body weight than that of the mid-sized N.A. scatter hoarder squirrel species of N.A.
The Reds love dried fungi; it is often their habit to harvest them and carry them up high into the crown of trees to store them till they dry, where they can then last longer as a future source of food.
Both, 'Chanterelle (Summer) and 'Yellow Feet' winter mushrooms, which are very similar, are available in both pieces and dried ground mushroom powder from, "Oregon Mushroom". Best to give them a call directly; they are very helpful and friendly family run company. Just like for the red squirrels that store them to dry, the small package lasts for many months. Good to include daily as part of the daily faire, they supply good source of trace minerals that are also needed in the diet.
https://www.oregonmushrooms.com/c-31...mushrooms.aspx