Diet or Nutrition is the basis of health.
Contrary to popular belief, squirrels eat a very wide variety, and very few nuts. They find nuts the same times of year that we do, during the fall when they need to gain weight for Winter insulation. They hide them and forget where they hid most them, and many times the nuts turn into trees. They eat grasses and weeds, leaves, the nutrient-rich center of twigs and branches, fungi, snails, insects, spiders, bird eggs, baby birds, frogs, lizards, buds, seeds, flowers, fruits, and more... The variety gives them their nutrients and minerals, they forage for what they need, and the sunshine gives them their vitamin D for calcium absorption.
During infancy and their teenage months, their bones, brains, muscles, etc... are all trying to grow and develop. Like any species, they need optimal nutrition to develop properly. If they're to released, their survival depends on optimal health. The better you care for them, the longer they live, and happiness is directly related to their health. You cannot be happy if you're not healthy, so feeding them junk is not loving them.
Below I will lay out everything we know at this point in time in hopes that it will help rehabilitators, disabled squirrel parents, and the squirrels that people have captive. There are photos and ratio charts for reference below.
They nurse until they are at least 12 weeks old in the wild
Limited, high sugar, low nutritional value
First food and continued staple, required not optional
Must be limited, they need to eat their healthy foods first
Rainbow variety with a large leafy green base
At least 15 minutes at least twice a week
Help them to be familiar for release and meet needs
No matter their condition, they can still eat healthy
Neonates and juveniles require a milk replacer when they come into rehab at an early age. Having monitored babies born in my house and those raised by mothers, we know mother squirrels nurse their young until they're at least 12 weeks old. They're at a disadvantage when we raise them so we need to continue formula at least that long as well.
There have been major issues with both Fox Valley 23/40 and 20/50 and PetAg's Esbilac. Thousands died on Esbilac and upon testing, it was very low in most nutrients and about 60% of the lot numbers tested were coming back rancid. The malnutrition made them susceptible to diseases they should have been able to easily overcome. Fox Valley 32/40 has a tendency to cause deadly digestion issues, and 20/50 produces much smaller babies with thin coats and tails, and many of them just dropped dead out of nowhere this year. We went on a search for something better and ended up trying Royal Canin and Breeder's Edge Foster Care Canine.
Royal Canin caused some digestion issues, we had trouble with pinkies but we aren't sure if it was formula or not, and it was incredibly difficult to obtain. Babies 3 weeks and older looked fantastic on Royal Canine, they grew really well, were muscular and beautiful, and released. Breeder's Edge has really impressed us, but we are adding calcium carbonate to the powder when we mix it because it's calcium content is relatively low. t's ready mix, it doesn't have to sit for hours before you feed it, and the babies are thick, muscular, agile, with thick coats and a much more natural growth rate in general. Breeder's Edge babies grew nearly twice as fast as Fox Valley 20/50 babies. Another perk to this formula is that it's packed with fact and protein so you cannot feed it as often as you do the lesser formulas. We had fat flyers and pinkies on 4-5 feedings a day. If you try to feed more often they get diarrhea if they'll eat at all, because they simply don't need that much.
We mix Breeder's Edge:
1 heaping part powder
3 parts really hot water
-- Calcium Carbonate:
Amount to add per measure of dry formula powder:
1 teaspoon: 19.7 mg
1 tablespoon: 59 mg
**Don't mix more than you'll use in a day. Discard after 24 hrs
Rodent block offers basic nutrients with protein and other supplements added to give a kibble for them to snack on and try to be sure nothing is missed with vegetables. Block is a required staple, not optional, and they will all eat it, period. There are several options:
Henry's Healthy Pets offers a variety of block options; different flavors and protein content that are healthy. I bake them for mine here and there and have a few I feed them to for odd and assorted reasons. This is usually the best option for people with one or just a couple of squirrels. They are loaded with nutrients and veterinarians have told us that one a day is plenty.
Mazuri Rodent Breeder 6F #5M30 is sold in 50 lb bags. You can special order it through any store that carries Purina products if they are willing to order it. You have to order about 3 weeks in advance but a 50 lb bag runs around $30 unless you order from Tractor Supply, they sell for about $35.
*This is what I feed and depending on the squirrel's weight I feed anywhere from 1/4 to 1/3 of a cup per day. It's economical and the calcium:phosphorus content is nearly 2:1. I like the fact that they have something healthy to munch on throughout the day that doesn't break the bank. I've also never had a squirrel turn it down, even wild adults.
Mazuri rat and mouse is sold in 2 lb bags and I do order 25 lb bags in a pinch, but the calcium content is lower, so you need to account for that in your salads if you use it.
Oxbow, Harlan-Teklad, Kaytee and a few others sell rat and mouse block too. They'll eat Kaytee but it's expensive for the quality in my opinion. My resident squirrels will eat most any block, but they do not like Oxbow or Harlan-Teklad so I don't normally recommend them since I've gotten the same feedback from others.
Large leafy green base, and a rainbow variety of other vegetables chopped about the size of the end of your thumb (see size reference in photo below). Vegetables of different colors are concentrated in different nutrients so you want to hit as many colors as possible. You also have to be sure you're balancing their calcium to phosphorus ratio and limiting high oxalate foods, because all vegetables have different ratios.
Greens they'll usually eat are kale, green leaf lettuce, spring mix, romaine, collards, and more. The charts below will give more ideas. I also feed broccoli, cauliflower, butternut squash, buttercup squash, acorn squash, zucchini, yellow squash, sweet potato, carrot, sugar snap peas, snow peas, celery, cucumber, bell peppers, artichokes, and more...not at the same time. I change the vegetables out so they get different things each day. Change it out and keep it interesting.
Wild foods are a good addition, things from outside that they'd eat naturally in the wild, aside from insects that can and do carry parasites. If you're going to feed insects, try to use what you can buy from the Pet Stores so you don't give the animal/s in your care parasites.
Pine cones, dandelion, glover, leafy branches, clover, crepe myrtle buds, flowers, seeds, dogwood buds, flowers, seeds, bradford pear buds, flowers, seeds, magnolia cones, rose buds, flowers and hips, etc... Avoid acorns you find on the ground, they can grow mold on the nut, inside of the shell and it's deadly if ingested. Avoid mushrooms from the yard, it's hard to be sure of what you're picking. Don't go crazy with any one thing, just a bit of each so you don't overdo it. Be sure you don't pick foods from places that spray with pesticides.
Fruits have very little nutritional value and are loaded with sugar. If you feed mostly fruit, they'll pick out the fruit and won't eat their healthy variety. The idea is to give them a variety of just enough so they actually eat all of it, not to load down their plates with tons of everything so they fill up on one thing and leave the rest. I advise limiting fruit to one piece per day, the same size as you cut your vegetables or one grape for example.
Avocado is also considered a fruit and they LOVE it, but it's loaded with phosphorus and fat. If you have an overweight squirrel or the squirrel doesn't eat a lot of high calcium foods, you need to be really careful with how much avocado you feed. You need to calculate it into your total calcium to phosphorus ratio. Tomatoes are also high in sugar but also acid so go easy, the thumb size applies to everything but greens.
Fruits need to be considered a treat and are noted in the treat category. Remember, you want nutrients in them, not just filling up on sugars.
Any kind of human food is junk basically. Cookies, candy, cake, french fries, pizza, etc... is something they all love, but it's not at all good for them and they will get fat and unhealthy. Everyone gives their squirrels some sort of junk, but you can't go crazy. No whole cookies, french fries or chunks of cage, candy and pizza. If you give them something like that aim small.
A french fry is like us eating a 2*4, a cookie the size of a whole pizza to you and me, and so on... Most grey squirrels weigh about a pound down south and 1 1/2 to 2 lbs up north, a fox squirrel 2-3 lbs. Think about them and what they get in relation to their size. Another example is a teaspoon of whole milk vanilla yogurt or ice cream, not a scoop or more. They're tiny!
Grains, mostly cereal forms, are not a necessary part of diet but they will get them in whatever block you feed. They're mostly carbs which the body turns into sugars, so you want them avoid cereals, especially in juveniles. They should definitely not be a part of baby diet. If you want to make cereals a treat for an adult, it won't hurt anything, just small amounts keeping their small size in mind. Ex. 4-5 Cheerios
Nuts and seeds go in this group as well. Everyone wants to feed squirrels nuts and they love them, but they are the number one contributor to Metabolic Bone Disease. Nuts, seeds, mushrooms, avocado, corn, beans (includes peanuts), banana, etc... are all really high in phosphorus so you need to be aware of proportions and how often you feed them. For example, one nut a day, an avocado chunk, a chunk of corn, a pinch of seeds, or a slice of banana, and no peanuts or peanut butter to captive squirrels. Do some calculations and see what you're feeding a few times so you can get an idea of what kind of ratio you're feeding, it's not hard to get the hang of. Fruits are really a treat too and that's why they're limited too.
Some nuts are healthier than others because of their phosphorus content (see ratio charts). Nuts like black walnuts and hickory nuts are good for tooth wear because they have have to work hard to get into them and they don't get a lot of nut.
Yes, natural sunlight is part of diet! Sunlight is how they get their vitamin D, and vitamin D is what lets them use the calcium that they eat. The benefits of natural sunlight cannot be absorbed through any glass or screen, it filters out the beneficial rays, so they need to actually go outside in a secure cage or carrier at least twice a week for at least 15 minutes at a time. The more the better, but many don't like to be outside so that's the minimum. A small bird cage that you can take outside is sufficient, but be sure to pay attention to temps, because squirrels can overheat in direct sunlight in as little as 10 minutes. Early morning or later in the afternoon are usually better and consider giving them a cool treat to eat during that time to keep them cool and busy/distracted. Mine love frozen fruit, frozen Henry's blocks, frozen whole milk vanilla yogurt dollops, and frozen "yogurt balls". (yogurt ball recipe in the Compromised section below) Sunlight is a very good and free weapon against Metabolic Bone Disease.
Many captive and injured squirrels have issues with their teeth and/or their neurological state that prevents them from being able to eat normal block and salad, but you can still get a full, healthy diet in them with no problem. You'll see many people feed junk and formula, claiming its because they can't eat anything else, but they can. Adult squirrels should not be fed formula, it is formulated for growth and has much higher concentrations of nutrients than they need, causing elevated blood levels of those nutrients. Too much of a good thing is bad too, so keep formula for babies.
If you have a squirrel that can't eat block, there are several options. Henry's blocks are relatively soft, most squirrels can manage to eat them, and Mazuri blocks can be ground up and mixed with just enough whole milk vanilla yogurt to roll into balls. Yogurt is loaded with calcium, protein, and healthy fat, and they love it, so it makes a very healthy, soft block option.
For their vegetables, you just chop your salad into a pot, steam it soft, and puree it in any kind of food processor. If you need to fee it with a syringe, make sure it's really soft with plenty of water, and plenty it into a liquid. If it just needs to be soft you don't have to liquify it but you want it thin enough to transfer to ice trays to freeze, then you can transfer it from the ice trays to a labeled freezer bag for easy access. I usually make up several batches of different combinations so they don't get bored. Most of them like to gnaw the frozen cubes, but you can easily put it into the microwave to defrost/warm too. You can add rodent block to it, and a tiny bit of formula or yogurt for flavor. I like to load it down with papaya and a small amount of another fruit since papaya is relatively low sugar and great calcium content. They normally love their smoothie, but you can play with it if they won't eat it. Add stuff you know they like that is also healthy.
When you make a salad, you need a big leafy green base, as much as or more than everything else combined. Make sure you don't feed so much of everything else that they are too full to eat their greens. The photos below give you a good idea of what a salad should look like. The ratio charts below are important.
Some photos I took of veggies and fruits to steam for smoothies.
You have to consider the amount of calcium and the amount of phosphorus in the foods that you feed. Below you see charts with the Ca:Phos ratios from the FDA. When all is said and done with your salad and treats, your Ca count needs to be double your phosphorus count.
Look at "dried yellow corn for example. It's phosphorus level is 13.8 times it's calcium content, it's HORRIBLE for them because no matter what you feed in vegetables, you're not likely to get enough calcium for the day unless they eat collards, with 14.5 times the amount of calcium as phosphorus. You see Spinach and Watercress, they're at perfect 2:1, which means double the amount of calcium as phosphorus. Your total of the values needs to come up double the amount of calcium as phosphorus.
Now that said, you also have to take oxalates into account. Foods high in oxalates also inhibit calcium absorption/use. You can Google high oxalate foods but some include:
Beans, beets, berries, cranberries, dark green vegetables (collards, spinach, broccoli, kale, mustard greens, etc...), nuts, oranges, rhubarb, soy, sweet potatoes, white potatoes, tofu, grains, okra,
I want to be very clear. High phosphorus and high oxalate foods have to be limited, but they also have to be fed. They are part of healthy variety, you just can't go overboard with them and you need to make sure they don't outweigh calcium intake. You can also go very wrong trying to supplement, so I avoid supplements unless I have a case of Metabolic Bone Disease. You want to make sure they get everything they need from diet and sunlight, not additives. Too much calcium, nutrients in formula, trying to add Vitamin D (can be toxic and we don't know how to dose it and be sure it's safe), and so on can go very wrong and cause equally bad issues. Too much calcium for example can cause the exact same issues that too little can cause. The vest way I've found to keep mine healthy and to train is to get an idea of what they like that's higher in calcium and lower in oxalates, and always feed those. Then mix in the other things here and there throughout the week in smaller amounts.
**I added the Henry's chart at the bottom for those that need a visual.