more on cedar in nestboxes (long)

Kevin Li kdli at
Tue Mar 27 21:20:18 PST 2001

I just ran across a note from Louise Chambers of the Purple Martin
Conservation Association regarding cedar shavings in nest boxes, the post
Kevin Li
Ballard USA
kdli at

From: Louise C louise at Edinboro PA
Date: 5/30/00

Here's the Purple Martin Conservation Association's position and history on
cedar shavings. The PMCA conducted a four-year study to determine the
effects of nest parasites on the reproductive success of Purple Martins.
Over the course of the study, 2 identical martin houses placed 15 feet apart
were monitored. Each year, one house was treated to remove all parasites
from the nests, and the second house was left untreated as a control. The
results showed that the treated house fledged almost twice the number of
young as the control house. Clearly, one way to help martins was to reduce
the number of nest parasites, without exposing the martins and their
nestlings to any potentially harmful substances, such as Sevin. (Sevin may
work beautifully in the short term in reducing nest parasite populations,
but research suggests that its continued use will result in long-term
toxicity that may affect breeding success in the birds. In other words, it
will get rid of the parasites now, but the birds will suffer from poor
reproductive rates later on.) It's important to remember that the goal we
all have in mind is to help the martins fledge as many healthy young as
possible, not to eliminate every last nest parasite. Lice spend their entire
life cycle on the birds; the targets here are fleas, nest mites, blowfly
larvae, and bedbugs, all of which take blood meals from the birds, and spend
most of their time burrowed down in the nest debris. The simplest and most
direct method of controlling nest parasites is nest replacement (removing
all nest material about 10 days after young hatch. Replace with bed of clean
dry shavings or pine needles. Put nestlings back in nest. This one
replacement may be sufficient to knock parasite numbers down for the rest of
the nestling period, but in areas where blowflies are a problem, a second
replacement when young reach 17-20 days old may be necessary.) The PMCA
tested the martins' preference, and found they prefer a compartment or gourd
that contains shavings or other nest material to an empty compartment. So
the purposes of using cedar shavings are, to provide insulation against cool
spring weather, to save the martins time by giving them a prebuilt nest, to
repel nest parasites, and to allow for nest parasite control, via nest
replacements. The PMCA has used cedar shavings for six years (this will be
the seventh year), other landlords (Andy Troyer, for one) for nite years,
with 2000 being the tenth year. No ill effects have been observed in the
young or adults. Andy did find, however, that cedar shavings significantly
reduced blowfly parasitism at his site. We will continue to test cedar
shavings, and other types of bedding. For all of the purposes listed above,
though, (except parasite repellency) any type of wood shavings will do just
as well as cedar. Hardwood shavings, such as aspen or poplar, are suggested
by a US Fish & Wildlife health center; shavings from treated lumber and
hemlock are toxic to birds, and should not be used. The wildlife health
center could not find any data on problems from the use of cedar shavings in
bird boxes. Aspen shavings are the only wood shavings product approved by
the FDA and EPA for use by humans and animals. EPA data also confirmed that
cedar shavings may be effective in repelling blowflies. When questions arose
about the safety of cedar shavings for martin nests, we researched the topic
as thoroughly as we could. Both the Environmental Protection Agency, and a
wildlife toxicologist at the US Fish & Wildlife Lab in Patuxent, MD, found
no data showing cedar shavings were toxic or harmful to birds. They
commented that the only way to determine toxicity for sure was to do
specific tests, exposing Purple Martins to vapors from cedar shavings, then
destroying the birds, and analyzing them for signs of reaction to the cedar.
No one has done such tests, but they did find cedar listed as being
effective as a blowfly repellent. The EPA reported that cedar is exempted
from registration as a pesticide as it poses no risk to people or the
environment, unlike naphthalene, Sevin, etc. Contrary to what has been
published on other forums, Naphthalene (the compound in moth balls) is not a
component of cedar shavings. What is found in cedar is Cedrene and Cedrol.
Extracts from cedar (and other softwoods, such as pine) are in the broad
category of aromatic or volatile compounds such as hydrocarbons
(naphthalene, which is classified as a phenol, is also a member, but a
distinct compound), cedrene. Symptoms of overexposure to cedar shavings
include respiratory tract infections, sneezing, and discharge from
eyes/nostrils. We have observed none of these symptoms at the PMCA site, nor
have other landlords using cedar reported them Another factor to consider is
that we place cedar shavings in compartments in early April, just when the
martins are due to return here. By the time the first young hatch in June,
and vapors from the shavings have long since evaporated. We have suggested
that landlords can use aromatic cedar in the house to begin with, and use
other types of shavings, or dried pine needles, for changes after the young
have hatched. Nestlings would be more susceptible to any vapors than the
adults, so this method would minimize nestling exposure to any irritants
from the shavings. But for one-time use early in the season, cedar shavings
would be thoroughly aired out by the time the young hatch. But, PMCA
research participant Andy Troyer uses fresh aromatic cedar shavings on all
his nest replacements, as do other landlords, and have experience very good
success rates. Reproductive success and return rates from PMCA-monitored
sites strongly suggest that cedar shavings do not cause problems. Used in
conjunction with nest replacement at some sites, and with one time use early
in the spring at control sites, we have documented 95.5% success rates
(hatch to fledge.) This is a statistically significant higher than average
success rate for our region. Furthermore, since all nestlings and many
adults at PMCA-monitored sites are individually color banded, we have been
able to collect data on the survivorship of nestlings returning to their
natal area as subadults the following spring. These rates (20-30% of the
nestling Purple Martins that we banded are observed back as subadults) also
strongly suggest that the use of cedar shavings is not having any ill
effects on the birds. The return rate is twice the published norm return
rate of banded young to their natal site. Also, throughout their
evolutionary history, Purple Martins have nested in cedar trees, preadapting
them to any potentially-harmful vapors. It is not a bad thing to be cautious
about using new materials or management ideas. Our goal, ultimately, is to
impact the martins in a positive way. Based on the data the PMCA has been
collecting, using cedar shavings and nest replacement are resulting in
higher than average success rates. We will continue to collect information
on cedar shavings, and to try new ideas. This year, we are planning to use
soft, dried pine needles in 1/2 the compartments, on the recommendation of
Dr. Thomas B. Dellinger, who has found they maintain a better nest bowl
shape than shavings, and that they drain more quickly after a rain. Offering
compartments with both cedar shavings and pine needles will allow the PMCA
to compare results, and share them in the Update and other forums for martin


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