Bird food nutrition: fat, protein and energy density compared

The short answer

• Fat is what keeps a small bird alive overnight in winter: suet at about 75% fat and sunflower kernel at about 51% are the two dense options.
• Protein matters most during molt and the nesting season, which is when mealworms and peanuts earn their price.
• A small songbird can burn close to 10% of its body mass overnight in hard frost, which is why feeder timing at dawn and dusk matters more than feeder volume.
• Grains such as millet and cracked corn are low in fat and are maintenance foods, not survival foods.
• Water and grit are nutritional inputs too, and both are hardest to find in exactly the weather that makes them matter.

Bird food is usually discussed as a list of preferences. It is more useful to think of it as three nutrients doing three jobs at three different times of year.

Prices are 2026 United States big-bag benchmarks used as defaults in our seed cost calculator. Swap in your own and the ranking can change; the edible fraction and energy columns will not.

Fat: the overnight budget#

A chickadee weighs about 11 g. On a long January night at -10 °C it can burn close to a tenth of its body mass staying warm, and it has to replace all of it during the following day's short hours of light. That is the whole reason high-fat foods matter in winter, and it explains two practical rules that otherwise sound like folklore.

Fill feeders before dawn. The most valuable hour of the day for a small bird in a cold snap is the first one, because the overnight deficit is at its worst.

Do not let feeders run empty at dusk. The last feeding of the day is what the bird carries into the night.

Suet, sunflower kernel and peanut kernel are the three foods that deliver fat efficiently. Nyjer is respectable at about 35%. Everything grain-based is not in the conversation.

An overnight budget, worked through#

That claim as arithmetic. This is a model, not a measurement.

Assumptions. A black-capped chickadee at 11 g, the mass we carry in the dataset, roosting in cover through a 15 hour January night. Hard frost, around 14 °F (-10 °C), sheltered from wind. Overnight loss of about 10% of body mass, the figure usually quoted for small songbirds in severe cold. Fat at about 9 kcal per gram.

The working. Ten per cent of 11 g is 1.1 g, and not all of that is fat: some is water and gut contents. Call the fat component 0.7 to 1.1 g, so 6 to 10 kcal burned overnight. Round it to 8 and convert back into food using the densities in the table above.

At our working figure of 0.03 to 0.04 g for a black oil sunflower kernel, that night costs roughly 35 to 45 kernels, before the daytime cost of staying warm and foraging. Across nine hours of December daylight it is one kernel every 13 minutes with nothing spare. At the other end of the scale, an 11 oz suet cake holds roughly 2,300 kcal, close to 290 chickadee nights of that deficit, and a suet cage in a busy February yard still empties in a week.

The gap between foods is therefore a time gap as much as a calorie gap. A bird working on cracked corn must find, handle and swallow twice the mass a bird on suet does, on the shortest days of the year. That is a stronger argument against grain-heavy winter mixes than fat percentage alone.

Real birds do better than the model implies, because small songbirds lower their body temperature overnight, roost out of the wind and cache food in autumn. The direction of the answer holds: in a hard frost the limit is not the presence of food, it is the daylight available to turn it into fat.

Protein: molt and nestlings#

Two periods dominate a bird's protein demand. Growing a complete new set of feathers after breeding is expensive, and feathers are almost entirely protein. Raising chicks is more expensive still, and nestlings of nearly all our feeder songbirds are fed on insects rather than seed, even by species that are seed specialists as adults.

This is where mealworms and peanuts belong: as supplements in late spring, summer and early autumn, not as a midwinter strategy. It is also why the answer to "what should I put out for the baby birds" is almost always "nothing extra, and here is why", covered in feeding during nesting season.

Sugar: flight fuel#

Nectar occupies its own category. A hummingbird has the highest mass-specific metabolic rate of any bird, and it runs on sugar taken as it flies, with insects supplying the protein and fat. The 4:1 mix is not an arbitrary recipe: it is close to the sucrose concentration of the flowers these birds feed at, which is why it is worth being precise about it. The recipe and the reasons are in hummingbird nectar.

What "no-melt" and "high protein" do and do not mean#

Neither phrase has a regulated definition in wild bird food. Both describe something real, and both are read as promising more than they deliver.

No-melt is fat blended with a dry carrier, usually flour, cornmeal or ground grain, so the cake keeps its shape in warm weather. That is genuinely useful from late spring to early autumn. It does not mean higher fat: the carrier that stops the cake slumping also dilutes it, so fat percentage and energy density both fall below the table figures. It does not mean rancid-proof, because fat oxidises whether or not the cake is still a cube. And it is not a license to leave fat out in any weather. Above about 90 °F soft fat transfers to the face and chin feathers of birds that press into it.

High protein should be read against the protein column rather than the front of the bag: dried mealworms about 50%, shelled peanuts 26%, nyjer 21%, sunflower kernel 20%, safflower 16%, millet 11%, cracked corn 9%, suet 8%. A blend earns the phrase by containing something from the top of that list, and the phrase says nothing about how much. Two checks work better. Read the ingredient list in order, because the first ingredient by weight is what the product is, and a mix led by milo or wheat is a grain mix with a garnish whatever the front panel says. Then ask which month you are buying for: in January the limiting nutrient for a small bird is fat, and a low-fat high-protein blend is the wrong product sold with the right adjective. Our percentages are also kernel figures, so an in-shell seed delivers well under its kernel percentage per pound bought.

Water and grit, the inputs nobody counts#

Water. Birds need it every day of the year, and in a hard freeze open water is often scarcer than food. It is also a feather-maintenance question, which makes it an energy question: well-arranged plumage is insulation, and insulation is what the budget above rests on. Metabolizing fat releases some water internally, so birds on a high-fat winter diet drink less than you might expect, but the need does not disappear. What works is shallow and dull: 1 to 2 in at the deepest point, a rough surface for grip, and in freezing weather a heater rather than any additive. Never put antifreeze, salt or glycerine in a bird bath. Details in bird baths and water.

Grit. Seed eaters have no teeth. Seeds are ground in a muscular gizzard, and many species swallow coarse sand or fine gravel to do the grinding, and they find it themselves for most of the year on paths and bare ground. Under settled snow or ice those sources vanish at exactly the point the diet is driest. That is a cheap gap to fill: a saucer of coarse sand kept dry under cover beside a ground station, out of the seed, a handful lasting weeks. Calcium is the related item with its own season, and crushed eggshell in spring is the usual answer for females laying eggs.

Why density and usefulness pull apart by season#

Composition is fixed. Value is not. The same figures point at different foods depending on what is limiting the bird that month.

Dried mealworms are the highest-protein item in the table and one of the least useful in January. Suet is the densest energy in the table and the one item you may have to remove in July. Nothing in the composition changes between those two sentences, only the month, which is why this page sits beside the feeding calendar rather than replacing it.

Reading the table without over-reading it#

Three cautions.

These are composition figures for the food, not a diet. No wild bird eats one food. A feeder supplies a fraction of a bird's intake, and the rest is seeds, fruit and insects it finds itself.

Blended products vary widely. A suet cake's fat percentage depends on what has been mixed into it. A cake bulked out with cornmeal and millet is not 75% fat. The figure here is for predominantly rendered fat.

Nutrient density is not the same as usefulness. Dried mealworms are the highest-protein item in the table and one of the least useful in January, because what a bird needs then is fat and the mealworms cost seven times as much per pound. Match the nutrient to the month.

The derivation of every figure, including which are published values and which are our working estimates, is on the methodology page.

Frequently asked questions#

What is the highest fat bird food?

Rendered suet, at roughly 75% fat, is the highest-fat food in normal feeder use. Sunflower kernel and peanut kernel follow at around 50%, and nyjer at about 35%. Those four are the winter energy foods. Millet, cracked corn and most cheap mix ingredients sit at 4% or less, which is why a corn-heavy mix performs badly in a cold snap regardless of how much of it you put out.

Do birds need protein from feeders?

They need it, but usually not from you. Wild birds obtain most of their protein from insects, and that is especially true during molt and while feeding nestlings. High-protein feeder foods, mealworms above all, are useful supplements during those windows and largely redundant in midwinter, when the limiting nutrient is fat and the limiting resource is time to find it.

Is peanut butter safe for birds?

Yes, in the ordinary sense: plain unsalted, unsweetened peanut butter is a legitimate high-fat food and is widely used in homemade suet. The old warning about birds choking on it is not supported. What matters more is quality and rancidity: buy plain, keep it cool, and put out small amounts in weather where fat will not melt and coat feathers.

Why is nectar so low in energy density?

Because it is 80% water by design. A 4:1 nectar mix runs about 68 kcal per 100 g, which looks trivial next to suet at 740. That is the correct concentration: it matches the sucrose content of the flowers hummingbirds evolved to feed on, it is what their gut processes efficiently, and a stronger mix ferments faster without helping the bird.

Does no-melt suet have less fat?

Usually yes. A no-melt cake is fat blended with a dry carrier such as flour, cornmeal or ground grain so it holds its shape in warm weather. The carrier is what stops it slumping, and it also dilutes the fat: the roughly 75% figure in our table is for a cake that is predominantly rendered fat. You are trading energy density for shape stability, which is a fair trade in July and a poor one in January. No-melt is also not rancid-proof. Fat oxidises on a schedule set by heat, light and air, whatever shape the cake is in.

Do birds need grit or eggshell at a feeder?

Seed-eating birds grind food in the gizzard rather than chewing it, and many swallow coarse sand or fine gravel to help. They normally find it themselves on paths and bare ground, so it only becomes worth offering when snow or ice covers those sources. Crushed eggshell is a different thing: it is calcium, and it matters most to females laying eggs in spring. Rinse the shells, bake them at about 250 °F for 20 minutes, crush them small and offer them in a separate dish rather than mixed into seed.

Sources and further reading

1. FoodData Central US Department of Agriculture Composition values for sunflower, safflower, peanut, millet and corn
2. All About Birds: Feeding Birds Cornell Lab of Ornithology Which foods suit which seasons and species