Bird Feeding Glossary

The short answer

• Hulled sunflower and sunflower hearts are the same product; nyjer and thistle are the same product and neither is a thistle.
• Kernel yield is the term that changes what you pay: it converts price per pound bought into price per pound actually eaten.
• Three feeder-borne diseases have names worth recognizing on sight: salmonellosis, trichomonosis and mycoplasmal conjunctivitis.
• Words like premium, gourmet and no-waste have no agreed meaning on a seed label. Kernel yield, protein percentage and seed names do.

Definitions as this site uses them, which is not always how a seed bag uses them. Terms with a full guide behind them link to it; the rest are defined here and nowhere else because they do not need a page of their own.

The four confusions worth clearing first#

Hull and hulled. The hull is the shell. Hulled seed has had it removed, so hulled sunflower, sunflower chips and sunflower hearts are three names for one product. The difference is not nutritional, it is arithmetic: with the hull gone you stop paying for weight the birds discard.

Thistle and nyjer. Same bag, different name, and neither is a thistle.

Suet and no-melt suet. Plain suet is rendered beef fat. No-melt is fat cut with flour or cornmeal so it holds shape in heat, at some cost in energy density.

Kernel yield. The number that connects the other three to money.

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.

A to C#

aflatoxin#

A toxin made by Aspergillus molds growing on damp grain, worst in corn and peanuts. It is invisible, it survives storage, and it can kill a small bird at a dose that leaves no other sign. It is the reason caked or sour-smelling seed goes in the bin rather than in the feeder.

ant moat#

A small cup fitted above a nectar feeder and filled with plain water. Ants cannot cross it, so they never reach the ports. Refill it every few days in heat. Never put oil in one: it transfers to feathers and wrecks their insulation. See ants on nectar feeders.

baffle#

A dome or cylinder fitted to a pole or hanging line to block a climbing animal. Position decides whether it works: on a pole, the top of the baffle needs to sit about 4.5 ft up with 8 to 10 ft of clear air on every side. See baffles and poles.

bee guard#

A plastic grid or cage over a nectar port that admits a hummingbird bill and excludes bees and wasps. Saucer-style feeders make guards unnecessary, because the syrup sits well below the port where an insect cannot reach it. See bees and wasps.

bird guardian cage#

An outer wire cage, usually about 1.5 in mesh, surrounding a seed or suet feeder. Chickadees, finches, nuthatches and titmice pass through it; squirrels, grackles and starlings do not. It is the most reliable exclusion device with no moving parts. See squirrel-proof feeders.

black oil sunflower#

The small, thin-shelled sunflower seed that is the default feeder food across North America. It has the broadest appeal of any single seed, runs about 51% fat, and yields roughly 75% edible kernel by weight. See black oil sunflower.

brush pile#

A loose stack of prunings and cut branches near the feeding station. It gives a small bird a two-second escape from a hawk or a cat, and adding one usually raises the number of species willing to feed in the open. See native plants and cover.

caching#

Storing food for later. Chickadees, titmice, nuthatches and jays all cache, taking one seed at a time and leaving with it. This is why a feeder can empty far faster than the visiting birds could possibly eat, especially in the two weeks before a cold snap.

cracked corn#

Maize broken into pieces for ground-feeding birds: doves, juncos, sparrows, quail and jays. It is the cheapest food per pound on this site and the lowest in energy density, and it is the food most likely to bring deer and rodents. See cracked corn.

crop#

A muscular storage pouch at the base of a bird's throat, ahead of the stomach. It lets a bird load up quickly in an exposed place and digest the food later somewhere safer, which is exactly what a visiting flock is doing when it strips a feeder in ten minutes and disappears.

crop milk#

A protein-rich secretion produced by the crop lining of pigeons and doves and fed to their young. It is why a Mourning Dove pair can raise chicks on a seed diet, without the insect hunting almost every other feeder species has to do in the nesting season.

D to I#

dominance hierarchy#

The pecking order at a feeder. Larger and pushier species displace smaller ones, so what you see is not what is present. Putting a second feeder out of sight of the first, rather than beside it, often reveals a species list you did not know you had.

dripper#

A slow drip fitting mounted above a bird bath. Moving water is audible and visible from much further away than still water, and it pulls in warblers, vireos and thrushes that will never touch a seed feeder. See bird baths and water.

gape#

The width of a bird's open bill, and by extension the largest item it can swallow or handle. Gape explains why a chickadee carries a sunflower seed off to hammer it open while a grosbeak simply crushes the same seed in place and swallows the kernel.

guild#

A group of species that exploit a resource the same way regardless of family. Clinging bark feeders (woodpeckers, nuthatches, creepers) are one guild; ground gleaners (juncos, sparrows, doves) are another. Feeder design selects by guild, not by species, which is why one feeder brings four birds that look nothing alike.

hopper#

A feeder with an enclosed chamber that meters seed onto a tray by gravity, usually house-shaped with a pitched roof. High capacity, good weather protection, and easy for a squirrel to empty unless the pole is baffled. See hopper feeders.

hull#

The hard outer shell a bird strips off and drops. Hull is weight you paid for and rubbish you sweep up, and piled sunflower hulls also suppress plant growth underneath the feeder. See seed waste and mess.

hulled seed#

Seed sold with the hull already removed. Nothing is wasted and nothing accumulates on the ground, but hulled seed takes up water fast, spoils sooner and should be bought in quantities you will use within a few weeks. See sunflower hearts.

irruption#

A winter movement of northern birds far south of their usual range, driven by failure of the conifer, birch or alder seed crop rather than by cold weather. Irruption years put siskins, redpolls and grosbeaks on feeders that normally never see them.

irruptive species#

A bird whose winter range shifts by hundreds of miles between years: Pine Siskin, Evening Grosbeak, Common Redpoll, Red-breasted Nuthatch. Their absence one winter says nothing about your feeder, your seed or your setup.

K to M#

kernel yield#

The fraction of a bag that is edible once the hull is discarded. Our working figures are 1.0 for sunflower hearts, 0.75 for black oil, 0.65 for safflower and 0.6 for striped sunflower. Dividing price by kernel yield gives price per pound eaten. See cost per calorie.

mealworm#

The larva of the darkling beetle, sold live or dried. At roughly 50% protein dried it is the highest-protein food on the feeding station, and it is the only dependable way to bring bluebirds and wrens to a feeder. See mealworms.

milo#

Sorghum: a round reddish grain used as cheap bulk in low-grade mixes. Most eastern feeder birds refuse it and rake it out to reach the sunflower, where it feeds rodents instead. Some western ground feeders and quail do eat it. See reading a mix label.

molt#

The scheduled replacement of worn feathers, usually late summer into autumn. It is expensive in energy and protein, which is why feeders stay busy in August and why birds in molt look ragged and behave far more secretively than they did in June.

mycoplasmal conjunctivitis#

A bacterial eye disease of House Finches and other finches, seen as swollen, crusted or closed eyes. Affected birds go blind and starve rather than dying of the infection itself. It spreads on feeder surfaces. See diseases at feeders.

N to P#

nectar#

Sugar water for hummingbirds and orioles, made at four parts water to one part white granulated sugar and nothing else. No dye, no honey, no brown sugar, no artificial sweetener, no supplements. See the nectar recipe.

nestling#

A chick still in the nest and not yet feathered enough to leave it. A nestling found on the ground should be put back if the nest is reachable. A fledgling, hopping about with a short tail while its parents watch, should be left exactly where it is.

no-melt suet#

A suet cake blended with flour, cornmeal or vegetable fat so it holds shape at higher temperatures. It softens rather than running, which makes warm-weather suet feeding possible, but it is not heat proof and still goes rancid. See suet.

nyjer#

A small black oilseed, Guizotia abyssinica, imported from Africa and Asia and eaten mainly by goldfinches, siskins and redpolls. Sold as thistle although it is not one. High in oil and quick to go stale once opened. See nyjer seed.

passerine#

A perching bird of the order Passeriformes, with three toes forward and one back and a tendon arrangement that grips automatically when the leg bends. Nearly every songbird at a feeder is a passerine. Woodpeckers, doves and hummingbirds are not.

perch length#

How far a perch projects from the feeder body, and the detail that quietly decides your species list. Under about 2 in you have a small-bird-only feeder; 4 in and over lets cardinals and grosbeaks balance and feed. See tube feeders.

pericarp#

The botanical name for the seed coat, the layer a bird removes to reach the kernel. On sunflower it is thin and splits along a seam. On safflower it is thicker and more awkward, which is part of why squirrels give up on safflower sooner than on sunflower.

plumage#

The complete set of feathers on a bird, including its current seasonal state. Breeding, non-breeding and juvenile plumages of one species can look like three different birds, which is behind most misidentifications at a feeder in late summer.

port#

The opening a bird feeds through. Ports are sized for one food and one only: a 3/8 in sunflower port pours nyjer straight through onto the ground, and a 1/8 in nyjer slit jams solid the first time somebody fills the tube with sunflower.

proso millet#

Small, round, cream-colored seed and the top-rated food for juncos, sparrows and doves. It is the one cheap grain worth buying deliberately, and it belongs on the ground or a low tray rather than in a tube. See white proso millet.

R to S#

rendering#

Melting and straining animal fat to remove water, meat scraps and connective tissue. Rendered fat keeps at room temperature; unrendered trimmings go rancid quickly and grow bacteria. It is the step that makes a homemade fat cake safe. See homemade suet.

roost#

Where a bird sleeps, and the act of doing it. Overnight survival in a cold snap depends more on a sheltered roost, a dense conifer or a cavity than on the last feed of the day, which is why cover near a station is not decoration. See native plants and cover.

safflower#

A white, thick-shelled seed taken by cardinals, chickadees, house finches and grosbeaks, and largely ignored by grackles and squirrels. Expect two to three weeks of the regulars ignoring it before they accept it as food. See safflower.

sallying#

Launching from a perch to take an insect in mid-air and returning to the same perch. Bluebirds, phoebes and flycatchers feed this way, which is why an open sight line and a low perch matter more to them than the contents of your feeder.

salmonellosis#

A bacterial infection spread through droppings on feeder surfaces and in spilled seed, especially lethal to siskins and goldfinches. Local outbreaks are the usual reason a wildlife agency asks people to take feeders down for a few weeks. See diseases at feeders.

scatter feeding#

Throwing seed directly onto the ground rather than into a feeder. It suits doves, juncos, towhees and sparrows, and it is the fastest route to a rodent problem if you put out more than the birds clear before dusk. See ground feeding.

seed bridging#

When damp seed sets into an arch inside a feeder and the column above it stops falling. The feeder looks full and delivers nothing, the ports sit empty, and the plug at the base is the part that goes moldy first. It is the most common tube feeder failure.

seed catcher#

A tray or mesh basket fitted under a feeder to collect dropped hulls and seed. It keeps the ground clean and gives large birds somewhere to stand, but it must be emptied, or it becomes the wettest and moldiest part of the station. See seed waste.

shepherd hook#

A single curved pole pushed into the ground to hang a feeder from. Cheap and easy to move, also easy for a squirrel to climb and easy to bend under a full feeder, so it needs a baffle and a proper ground socket. See poles and hooks.

sterilized nyjer#

Nyjer heat-treated at import so it cannot germinate, which is a condition of bringing it into the country. The heating also shortens its useful life, so old nyjer is dry, low in oil and simply ignored by finches that took it happily last month. See nyjer.

suet#

Hard fat from around the kidneys of cattle, and by extension any rendered fat cake fed to birds. At roughly 75% fat it is the densest energy source on a feeding station, which is why woodpeckers and nuthatches build winter routines around it. See suet for birds.

suet plug#

A cylinder of suet pushed into a drilled hole in a log-style feeder. It feeds more slowly than a cake, is more awkward for starlings to strip, and suits clinging birds that can brace against wood. See cakes versus plugs.

sunflower hearts#

Sunflower with the hull removed, sold as hearts or chips. Every gram is eaten, so nothing rots underneath, at roughly twice the price per pound of black oil sunflower and about 44% more per pound actually eaten. See sunflower hearts.

T to Z#

tail prop#

A stiffened, pointed tail that a woodpecker or a creeper braces against bark to act as a third leg. It is why a suet cage with a tail board extending below it holds woodpeckers steadily and suits starlings, which have no tail prop, far less well. See suet feeders.

thistle sock#

A soft mesh bag filled with nyjer. Finches cling to the fabric directly, so it needs no perches and costs very little, but it wets through in rain, cannot be washed properly and should be replaced each season. See sock versus tube.

torpor#

A controlled overnight drop in body temperature and metabolic rate that hummingbirds use to survive cold nights on a tiny fat reserve. A torpid bird looks lifeless and can take many minutes to rouse. Leave it alone. See Anna's Hummingbird.

trichomonosis#

A protozoal disease that produces lesions in the mouth and throat, so an affected bird cannot swallow and starves with food in its crop. It spreads through shared water and wet food, and affects doves, finches and the hawks that eat them. See diseases.

tube feeder#

A clear vertical cylinder with feeding ports and perches down its sides, fed by gravity. The default small-bird feeder for chickadees, titmice, nuthatches and finches. Its failure modes are wet seed, chewed ports and a base that will not open. See tube feeders.

weight-activated feeder#

A feeder whose perch ring drops under a set load and closes the ports, excluding squirrels and often grackles too. Effective and adjustable, with a mechanism that eventually stiffens, clogs or freezes. See caged versus weight-activated.

window film#

Patterned film, dot arrays or external cord screens applied to glass to break up the reflection birds fly into. Spacing is the whole trick: marks no more than about 2 in apart, applied on the outside surface, not the inside. See window strikes.

zygodactyl#

Having two toes forward and two back, the foot arrangement of woodpeckers. Combined with a tail prop it turns a vertical trunk into a stable working surface, and it is why a vertical suet cage suits woodpeckers and frustrates most other birds.

Label words that are not terms#

These appear on packaging and mean nothing measurable. Read the ingredient list instead.

Frequently asked questions#

Is nyjer the same as thistle seed?

Yes as a product, no as a plant. Bags labeled thistle contain nyjer, the seed of Guizotia abyssinica, an African and Asian oilseed that is not a thistle and will not spread thistles through your garden. The name stuck from early marketing. All nyjer imported into the United States is heat-sterilized so it cannot germinate, which is also why stale nyjer is a real problem: sterilizing shortens its shelf life.

What does kernel yield actually mean for my seed budget?

It is the fraction of the bag you can eat if you are a bird. Black oil sunflower is roughly 75% kernel, so a pound bought is about 0.75 lb eaten and the rest is hull on the ground. Striped sunflower is about 60%. Sunflower hearts are 100%. Divide price per pound by kernel yield to compare foods honestly, which is the whole point of the cost per calorie page.

What is the difference between squirrel-proof and squirrel-resistant?

Nothing legally, and quite a lot practically. Neither term is regulated, so both appear on packaging with no standard behind them. On this site, resistant means the design slows a squirrel down or excludes most of them, and proof means the squirrel physically cannot reach the food. A caged feeder on a correctly baffled pole is proof. A feeder with a weight mechanism hanging from a tree branch is not.

What is the difference between a nestling and a fledgling?

A nestling is a chick that is still in the nest and not feathered enough to leave it. If you find one on the ground and the nest is reachable, put it back. A fledgling has left the nest on purpose: it is feathered, has a short stubby tail, hops rather than flies well, and has parents watching from cover and still feeding it. Fledglings on the ground are normal and should be left alone. The distinction matters because most rescues of healthy fledglings are kidnappings.

Sources and further reading

1. All About Birds Bird Academy and species guide Cornell Lab of Ornithology Anatomy, plumage and behavior terms
2. Common Feeder Bird Diseases Cornell Lab of Ornithology, Project FeederWatch Disease names, signs and feeder hygiene response
3. Wildlife Health Information USGS National Wildlife Health Center Salmonellosis and trichomonosis in wild birds