Is Dog Hair Safe for Birds' Nests?

The short answer

• Do not put out fur from a dog or cat that gets a spot-on flea and tick treatment. A UK study found fipronil, a spot-on insecticide, in the fur lining of all 103 tit nests it tested.
• Nests with more insecticide in the lining held more dead chicks or unhatched eggs. A 2026 follow-up found the levels in the fur tracked the levels in those eggs and chicks.
• No source gives a safe gap after a dose. SongBird Survival says treatments can stay on fur for up to 28 days, and the usual dose comes every 28 days.
• Fur from an untreated dog can line a nest if it is soft and short. NestWatch says human hair longer than 1 inch tangles like string, and this page holds dog fur to the same line.
• Dryer lint, yarn, string, thread and fishing line are all out. Moss, lichen, twigs, rootlets, plant fluff and untreated grass clippings are the safe offer.

Dog hair is safe for birds' nests only if the dog gets no flea and tick treatment and the hair is soft and short. Fur from a pet on a spot-on product should go in the trash, because a UK study found the flea drug fipronil in the fur lining of every one of the 103 nests it tested. Dryer lint, yarn, string and fishing line are out for everyone.

That is a change. Laura Erickson recommended setting out pet fur in her 2006 book, 101 Ways to Help Birds, and after the first paper she asked owners of treated pets to put the fur in the garbage instead. The new advice follows a pair of papers from 2025 and 2026.

What "nesting material" and "nest lining" mean#

Nesting material is anything a bird carries in to build its nest: twigs, grass, bark strips, moss. Many small birds finish the cup with a lining, a soft inner layer of fine grass, plant down, feathers or hair. The lining is the part that touches the eggs and the chicks, which is why fur matters more than a twig: whatever is on it sits against the brood for weeks.

A spot-on is a flea and tick liquid you squeeze onto a pet's skin, which on a dog means the neck. The 2026 paper says the drugs stay on the fur for a long time after that, often past the 28 day gap between doses. They can also spread through shedding, bathing, swimming and the home.

What the nest study found#

Cannelle Tassin de Montaigu and Dave Goulson of the University of Sussex, with chemists in Switzerland, tested fur-lined nests of blue tits and great tits. Volunteers sent in 237 nests from across the UK in autumn 2020, and 103 had fur that could be tested. The 2025 paper in Science of the Total Environment reports:

• 17 of the 20 insecticides screened for were found, with 2 to 11 in each nest.
• Fipronil was in 100 percent of nests. Imidacloprid and permethrin were each in 89.1 percent.
• Average levels were 115.5 ppb for fipronil, 376.3 ppb for imidacloprid and 231.1 ppb for permethrin. (ppb is parts per billion.)
• Nests with more insecticides, or higher levels, held more dead chicks or unhatched eggs.

The authors write that this is "suggesting" that contact with the lining "may lead to mortality". That is a link rather than proof, and the authors say so themselves.

The 2026 follow-up in Environmental Science and Pollution Research used the same nests and tested unhatched eggs from 24 of them and dead chicks from 35. Levels in the fur predicted levels in the eggs and chicks, with "significant positive correlations". The authors read that as the drugs moving from the lining into the young birds. Of the volunteers who kept a dog or cat, 83.9 percent said their pet was treated, with spot-ons, collars or tablets.

Why "wait a few weeks" does not work#

Take a dog that gets a spot-on on the first of every month. Suppose you brush it on March 15 and plan to fill a suet cage with the fur for the titmice.

The UK group SongBird Survival says treatments can stay on the fur for up to 28 days. March 15 is day 14, so the brushings are inside that window. March 29 is day 28, still inside it, and the next dose lands on April 1. A dog on a year-round monthly product never has a day when its fur is clear.

Now suppose the dog is dosed only from April to October. By March the last dose was five months ago. That sounds safe, but no source gives a gap after which fur is clean. The study's own fur sat in the nests for six to seven months, from spring building to autumn collection, and every sample still carried fipronil. So the rule is simple: if the pet gets a flea and tick product at any point in the year, its fur stays out of the yard.

SongBird Survival also advises owners who use spot-ons not to brush their pets outside. Brush indoors and bag the fur for the trash.

What to put out and what to keep in#

Collars and tablets. The volunteers' pets were on spot-ons, collars or tablets. No source we found tests fur from a pet on a collar or tablet alone, or says it is safe, so keep that fur in too. The same goes for an untreated dog that shares a home with a treated cat, since the 2026 paper lists the home as one of the ways the drugs spread.

Untreated fur. The National Aviary's Dr. Pilar Fish says soft dog hair can be used to line nests. But "if the hair is long or has a high tensile strength", it can wrap around birds and injure them. NestWatch, the Cornell Lab's nest project, puts a number on it: human hair longer than 1 inch "poses the same risk as yarn and string". The 2024 version of that page applied the same 1 inch line to hair from pets and livestock. No source gives a separate figure for dog fur, so 1 inch is the line this page uses.

Dryer lint. Laura Erickson notes that lint feels soft but "compacts and gets crumbly" once wet, which can weaken a nest. NestWatch adds a second reason: detergent chemicals and microplastics from synthetic fabric.

Yarn and string. You will still see "cut it under 4 or 5 inches", a figure from a 2010 post by Erickson that was common advice then. NestWatch now calls that advice outdated and says not to offer yarn at all. Yarns may be acrylic or nylon, and wool or cotton may carry dyes. Any stringy piece can wrap a chick's feet, wings or neck, trap it in the nest or cut off its air.

Fishing line. In July 2018 an osprey chick on a camera nest in Virginia became tangled in fishing line that a parent had brought to the nest. The wing damage was too severe to repair, and the chick was put down. If you fish, take used line home or to a recycling tube.

Which backyard birds line their nests with fur#

The study tested two European birds, and no North American feeder bird was in it. These are the ones that use hair in North America, from the nest notes in the Audubon field guide.

Titmice and chickadees nest in tree holes, and Audubon notes the Black-capped Chickadee also uses nest boxes. The 2026 paper calls blue and great tits cavity nesters that "routinely" use fur, so these are the closest match here. The titmouse may pluck hair from a live dog, so a treated dog resting on the deck in April is a source too.

What helps instead#

Birds find nest material on their own, and NestWatch says they "don't need help". If you want to offer some, mimic what your birds use in the wild: moss, twigs, leaves, lichen, rootlets, plant fluff such as cattail or cottonwood down, and grass clippings from a lawn with no fertilizer or pesticide. Put it in a clean suet cage or leave small piles on a deck rail, and swap it out after rain or at the first sign of mold.

Plants are the other route. Native shrubs and trees grow the caterpillars the chicks are fed on, as native plants and cover explains. If you keep hens, NestWatch says swallows, wrens and flycatchers may use their feathers, as long as the feathers have had no chemical treatment. Read bird feeders and backyard chickens before you put seed out near a flock.

Set material out in early spring, when the spring feeding jobs start and before birds build, since the bird feeding calendar puts the first nest building in April. The rest of the nesting season changes, from chopped peanuts to nest box checks, are on feeding during nesting season. Whether feeders draw ticks into a yard is a separate question, covered on ticks and bird feeders.

What this page does not cover#

This page is about what you set out for birds, and it is not advice on treating your pet. The fleas and ticks still need handling, and SongBird Survival suggests asking your vet about a treatment that weighs the effect on wildlife.

The study is from the UK, and it tested blue and great tits, not chickadees, titmice or any bird in the tables above. It measured residues and counted dead chicks, but it did not prove that the drugs killed them. It looked only for the 20 compounds on its list, so it cannot tell you that any other product, or a pet's fur months later, is clean.

Finally, the 1 inch line comes from NestWatch's advice on human hair, and no source has tested a safe length for dog fur. If you are unsure, skip the fur and offer moss.

Frequently asked questions#

Is dog hair safe for birds' nests?

Only if the dog gets no flea and tick treatment, and only if the hair is soft and short. The National Aviary says soft dog hair can line a nest, but long or strong hair can tangle around birds. NestWatch says human hair over 1 inch tangles like string, and no source gives a separate length for dog fur, so keep it under that. Fur from a dog on a spot-on treatment should go in the trash, because a UK study found the insecticide fipronil in the fur lining of every one of 103 nests it tested.

How long after a flea treatment is dog fur safe for birds?

No source we found gives a safe gap. SongBird Survival says spot-on treatments can stay on the fur for up to 28 days, and the usual label tells owners to dose again every 28 days. So a dog on a monthly product has no clean window. A 2026 paper also says the drugs often last on fur longer than the dosing gap.

Can I put dryer lint out for birds?

No. Laura Erickson notes that lint compacts and turns crumbly once it gets wet, which can weaken a nest. NestWatch adds that lint carries detergent chemicals and microplastics from synthetic fabric. Use moss, plant fluff or fine grass instead.

Is yarn or string safe for birds if I cut it short?

NestWatch now says no yarn at all. Yarns may be synthetic, and even wool and cotton may carry dyes or chemicals. Stringy material can wrap a chick's feet, wings or neck. The older advice to cut pieces under 4 or 5 inches comes from guides written before that change.

Should I brush my dog outside in spring?

Not if it gets a spot-on. SongBird Survival advises that owners who use spot-on flea and tick treatments do not brush their pets outside, because birds pick up the loose fur. Brush indoors and bag the fur for the trash.

Which North American birds use fur in their nests?

The Audubon field guide names animal hair in the nest lining of Tufted Titmouse, Black-capped and Carolina Chickadees, White-breasted Nuthatch, Chipping Sparrow, Song Sparrow and Northern Cardinal, with Eastern Bluebird and Dark-eyed Junco using it sometimes. None of them were in the UK study.

Sources and further reading

1. High prevalence of veterinary drugs in bird's nests (Tassin de Montaigu, Glauser, Guinchard and Goulson 2025, Science of the Total Environment 964:178439, doi 10.1016/j.scitotenv.2025.178439, CC BY 4.0) Elsevier, abstract via Europe PMC (PMID 39875313) 103 fur-lined blue and great tit nests; 17 of 20 insecticides found, 2 to 11 per nest; fipronil 100%, imidacloprid 89.1%, permethrin 89.1%; means 115.5, 376.3 and 231.1 ppb; more dead offspring or unhatched eggs with more insecticide, 'suggesting' contact exposure may lead to mortality
2. Transfer of veterinary parasiticides from the fur lining bird's nest to eggs and chicks (Tassin-de-Montaigu et al. 2026, Environmental Science and Pollution Research 33:7070-7081, doi 10.1007/s11356-026-37654-7, open access) Springer, full text via PubMed Central PMC13156203 Same nests, collected across the UK in autumn 2020; 24 nests with unhatched eggs, 35 with dead chicks; fur levels correlate with egg and chick levels; 83.9% of volunteers' pets treated (spot-ons, collars or tablets); residues often outlast the 28 day dosing gap; nest fipronil about 1,000 times below a dog's neck at four weeks
3. Veterinary drugs SongBird Survival If you use spot-on flea and tick treatments, do not brush pets outside or put out fur for nest making; treatments can remain on fur for up to 28 days
4. What Kind of Nest Materials are Best to Provide for Birds? (Holly Grant, 29 Apr 2021, updated May 2025) NestWatch, Cornell Lab of Ornithology Offer moss, twigs, leaves, lichen, rootlets, untreated grass clippings; untreated poultry feathers; no yarn; human hair over 1 inch poses the same risk as string (the 2024 version applied this to pet and livestock hair too); pet and livestock hair can harm nestlings; never dryer lint (detergents, microplastics)
5. 4 Common Materials That Could Be Harming Your Backyard Birds (Dr. Pilar Fish) National Aviary Soft dog hair can line nests; long or high tensile strength hair can entangle and injure; hair from dogs on topical flea and tick products is a risk
6. Dryer lint: Just say no! (2 Mar 2010) Laura Erickson, Twin Beaks blog Wet lint compacts and gets crumbly, weakening a nest; birds can tangle in yarns, threads or strings over 4 or 5 inches
7. Dog fur controversy? Laura Erickson's For the Birds (Substack) Recommended pet fur in her 2006 book; now asks owners of treated pets to put fur and treated clothing in the garbage
8. Plastic pollution hits home for OspreyCam followers (2018) Virginia Institute of Marine Science Osprey chick tangled in monofilament line in its nest in July 2018 and was euthanized; trash in almost all nests (Watts)
9. Guide to North American Birds (species accounts: nest) National Audubon Society Nest linings with animal hair: Tufted Titmouse (may pluck it from a live woodchuck or dog), Black-capped and Carolina Chickadee, White-breasted Nuthatch, Chipping and Song Sparrow, Northern Cardinal; sometimes Eastern Bluebird and Dark-eyed Junco