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Bird & Bat Prevention: Legal, Humane Exclusion in NH

TL;DR

Exclusion — netting, spikes, and sealing done at the right time — is HIGH-VALUE and humane. The hard part isn't the method, it's the law. Only pigeons, house sparrows, and European starlings can be excluded freely; every native bird and every New Hampshire bat species is legally protected, and bat exclusion is illegal from mid-May through mid-August, when flightless pups can't yet follow adults out.

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  • Legally unprotected birds

    Only pigeon, house sparrow, and European starling

    USFWS Federal Register, April 16, 2020 — every other wild bird in the U.S. is protected under the Migratory Bird Treaty Act.

  • NH bat exclusion blackout

    No bat exclusion mid-May through mid-August

    NH Fish & Game — the maternity season, when flightless pups can't follow adults out of the roost.

  • NH's bat population collapse

    Little brown bat hibernacula counts fell from 2,929 (2009) to a single bat (2014-15 surveys)

    NH Fish & Game — white-nose syndrome caused an estimated 99%+ decline.

  • The only legal bat removal method

    One-way exclusion devices, installed by or under a Wildlife Control Operator

    NH Fish & Game — WCOs may exclude bat colonies, not exterminate them.

The honest verdict

Does this actually work?

HIGH-VALUE and durable when timed correctly — the exclusion itself reliably works. The real risk isn't the method failing; it's doing it at the wrong time, which is illegal for protected species and can trap or kill young animals.

Works — High

Evidence: NH Fish & Game documents one-way exclusion devices as the sole legal method for bat removal, paired with a strict mid-May to mid-August no-exclusion window. USFWS federal rule confirms only three bird species are unprotected nationally. Both agencies frame timing, not technique, as the deciding factor in a successful, legal exclusion.

Works when

  • The species is correctly identified as protected or unprotected before any action is taken
  • Bird deterrents (netting, spikes, ledge modification) are installed before nesting season begins
  • Bat exclusion is done only after mid-August, once pups can fly, and before hibernation
  • Entry points are permanently sealed only after confirming the roost or nest is empty

Fails when

  • Bats are excluded during the mid-May to mid-August maternity season
  • A protected native bird's active nest is disturbed or removed
  • Entry points are sealed before confirming bats have actually left
  • Guano or nesting material is cleaned without a respirator
At a glance

The method works — the law decides when you're allowed to use it

How it works

Advanced DIY

Prevention here is physical exclusion — netting, spikes, and ledge modification deny unprotected birds a landing or nesting surface, while one-way devices let bats leave a roost but not re-enter, followed by permanent sealing once it's confirmed empty. None of it harms the animal; the entire method depends on being done at a legally and biologically appropriate time.

Vital stats

Time
A weekend for simple bird deterrents; bat exclusion is a multi-step project scheduled within the mid-August to October legal window
Best for
Buildings with ledges, soffits, gable vents, or attic access — Manchester's older brick and masonry structures and any southern NH home with open soffits or an accessible chimney.
Cost
Low for bird netting and spikes; moderate to higher for professional bat exclusion, chimney work, or roofline access

Netting, spikes, ledge modification, and one-way exclusion devices are genuinely effective at keeping birds and bats out of a building, and none of it requires killing anything. But this is the one method-type in the hub where the binding constraint isn't difficulty or cost — it's federal and state wildlife law. The Migratory Bird Treaty Act protects nearly every wild bird species in the U.S.; as of 2020, only the pigeon, house sparrow, and European starling are excluded from that protection, which means every other bird nesting on your building is legally off-limits to disturb.

Bats face an even tighter window. New Hampshire's bat populations have already been devastated by white-nose syndrome, and state law only allows Wildlife Control Operators to exclude bat colonies — never exterminate them — and never during the mid-May to mid-August maternity season, when pups too young to fly would be sealed in or separated from a roost they depend on. This page walks through what you can legally do yourself, what needs a licensed pro, and the calendar that keeps both humane and lawful.

Step by step

How to do it

  1. Identify the species before doing anything

    Determine whether you're dealing with a protected species (any native bird, any NH bat) or one of the three unprotected birds (pigeon, house sparrow, European starling). This determines everything that follows.

    Caution: When in doubt, treat the animal as protected — disturbing a protected nest or roost can carry legal consequences.

  2. Install bird deterrents before nesting season

    For pigeons, starlings, and house sparrows, install netting under eaves and rafters, spikes or slope modification on flat ledges, and screen vents with 1/4-inch hardware cloth — all before nesting season starts.

    Tip: Removing accessible food (spilled seed, exposed garbage) alongside physical deterrents keeps new birds from targeting the same site.

  3. Wait for the legal bat exclusion window

    For bats, do not attempt exclusion from mid-May through mid-August. Wait until after mid-August, once young bats can fly on their own.

    Caution: Excluding bats during the maternity season can trap or kill flightless pups — this is both inhumane and against NH Fish & Game guidance.

  4. Install one-way exclusion devices over confirmed exits

    Once the legal window opens, install one-way devices over identified bat exit points so bats can leave the roost but not return.

    Tip: A licensed Wildlife Control Operator can confirm all exit points are covered — missing even one leaves bats a way back in.

  5. Permanently seal entry points once confirmed empty

    After several nights of monitoring confirm no bats are returning, seal all entry points permanently with caulk and 1/4-inch hardware cloth.

    Caution: Sealing before confirming the roost is empty is the most common and most damaging exclusion mistake.

  6. Clean guano and nests safely

    Clean up droppings and old nesting material wearing an N95 or better respirator, gloves, and coveralls, since large guano accumulations can harbor the fungus that causes histoplasmosis.

    Tip: For a large accumulation, professional remediation is worth the cost over a DIY cleanup given the respiratory risk.

What you need

Tools & materials

  • Bird netting

    Physically block birds from nesting under eaves, rafters, and overhangs

    MBTA-permitted deterrent for pigeons, starlings, and house sparrows

  • Stainless-steel ledge spikes

    Prevent birds from landing on flat ledges and window sills

    Humane deterrent; does not harm birds

  • One-way bat exclusion devices

    Let bats exit a roost but not re-enter

    Install only after the mid-August legal opening

  • 1/4-inch galvanized hardware cloth

    Screen vents and cover confirmed-empty entry points

    The standard mesh size for permanent sealing

  • Silicone caulk

    Permanently seal small gaps once confirmed empty of bats or birds

    Apply only after exclusion is confirmed complete

  • N95 respirator, gloves, coveralls

    Protective gear for guano and nest cleanup

    Essential for histoplasmosis precaution

  • Bat house

    Optional replacement roost to keep a beneficial bat colony nearby after exclusion

    Bats eat large numbers of flying insects; a bat house offsets the loss of their original roost

Stay safe

Safety first

  • General

    Severe

    Never touch a bat with bare hands — bats can carry rabies. If a bat is found in a room with a sleeping person or unattended child, contact NH DHHS Bureau of Infectious Disease Control at (603) 271-4496 to assess exposure risk.

  • General

    High risk

    Large guano accumulations can harbor the fungus that causes histoplasmosis. Wear a respirator, gloves, and coveralls for cleanup, and consider professional remediation for significant accumulations.

  • Applicator

    Caution

    Rooflines, chimneys, and soffit access involve real fall and height risk — this is often safer and more effective as licensed, equipped work.

  • General

    Caution

    Disturbing a protected native bird's active nest, or excluding bats outside the legal window, can carry legal consequences under state and federal wildlife law.

Avoid these

Common mistakes

Why this method fails in practice.

  • Excluding bats during the mid-May to mid-August maternity season

  • Assuming any unwanted bird is a legal DIY target without confirming the species

  • Sealing entry points before confirming bats have actually left the roost

  • Cleaning guano or nesting material without a respirator

  • Disturbing an active nest belonging to a protected native bird species

New Hampshire context

Bird and bat prevention timing in New Hampshire

New Hampshire is home to several protected bat species — little brown bat, big brown bat, northern long-eared bat, eastern small-footed bat, and tricolored bat — with the northern long-eared federally listed and the eastern small-footed state-endangered. Manchester's older brick buildings and many southern NH homes with open soffits are classic pigeon, starling, and sparrow habitat, which is the legal DIY lane. For bats, the only responsible move is timing: wait for the August window, use a licensed Wildlife Control Operator for anything beyond simple deterrents, and never seal a roost you haven't confirmed is empty.

Peak season

Legal bat exclusion window: mid-August through October, before hibernation begins

First-frost anchor: Manchester first hard frost ~Oct 19 (50%) / Oct 29 (80%) per NOAA 1991-2020 — finish bat sealing before hibernation sets in, but only after the mid-August legal opening, never before it

Bird netting, spikes, and exclusion devices are DIY-legal for pigeons, house sparrows, and European starlings under the Migratory Bird Treaty Act. Native birds and all NH bats are protected; bat exclusion may only be performed by or under a licensed Wildlife Control Operator, and only outside the mid-May to mid-August maternity season.

UNH Cooperative Extension's bat resources reinforce the same rabies precaution NH Fish & Game gives homeowners: never handle a bat bare-handed, and call NH DHHS if one is found in a room with a sleeping person or child.

This method targets

Pests this applies to

When to call a pro

Bird Control / Wildlife with Anchor

Legal, humane bird and bat exclusion is specialized work — the species identification, the timing, and the height access all carry real consequences if done wrong. Anchor's licensed technicians handle species ID, MBTA-compliant bird deterrents, and NH-legal bat exclusion timed to the maternity-season rules.

Call us when…

  • You're not certain whether the bird or bat present is a protected species
  • Bats are roosting in an attic, soffit, or wall void
  • The work involves a roofline, chimney, or other height that's unsafe to access yourself
  • A protected native bird has nested somewhere you need cleared
  • Guano accumulation is large enough to need respiratory protection and proper disposal

Bird Control / Wildlife

free inspection; same-day service across southern and central New Hampshire.

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Keep them out

  • Install bird netting or spikes on ledges before nesting season begins
  • Never attempt bat exclusion between mid-May and mid-August
  • Seal confirmed-empty entry points with metal, not foam alone, once exclusion is complete
Common questions

Frequently asked

Sources & further reading(6)
  1. [1]
    USFWS Federal Register — List of Bird Species to Which the Migratory Bird Treaty Act Does Not Apply

    Only pigeon, house sparrow, and European starling are unprotected under the MBTA

    govverified 2026-07-13
  2. [2]
    NH Fish & Game — Bats and Homeowners

    Mid-May to mid-August maternity season exclusion prohibition, one-way exclusion device timing

    govverified 2026-07-13
  3. [3]
    NH Fish & Game — Homeowners and Bats (Nuisance Wildlife)

    One-way exclusion device use, guano/histoplasmosis hazard, rabies precaution

    govverified 2026-07-13
  4. [4]
    NH Fish & Game — Little Brown Bat Species Assessment

    White-nose syndrome population decline (2,929 in 2009 to a single bat in 2014-15); WCOs may exclude, not exterminate, bat colonies

    govverified 2026-07-13
  5. [5]
    AviAway — What Is the Migratory Bird Treaty Act?

    Netting, spikes, and wire as MBTA-permitted deterrent methods

    industryverified 2026-07-13
  6. [6]
    UNH Cooperative Extension — Bats in New Hampshire

    Rabies precaution and guidance on bats found in living spaces

    extensionverified 2026-07-13

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

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