|
One
of the things that is very hard for people who are
raising a wild baby bird to understand is that without
adult birds of its species for it to relate to,
the baby will imprint on the person raising it and
has no way to learn its song, the skills of survival
or the ability to join others of its species in
the wild. This is called human imprinting, and a
bird that has been imprinted by humans will not
survive in the wild. All birds that have been tested
imprint. This means that a bird becomes imprinted
on either birds, humans or even an object, depending
on who is raising them. Research has also shown
that most birds learn the song of their species
at a very young age. A baby bird, like a human baby,
needs to learn its language. The links below are
to articles and a NPR radio program on the research
into song learning in song sparrows.
PBR-All
things Considered
Singing
in the brain, University of Utah
Scientists Teach Sparrows to Sing Backward
Name
that tune: How birds learn to recognize song
Song in European Starlings has been studied extensively
in laboratory settings. It has been found that starlings
require "social teaching" by other starlings for
them to learn their song, as they are able to learn
only a little from taped songs. Click on the links
below to read some of these research articles in
your Adobe Reader.
Behavioural Biology
Institute of Behavioural
Biology, Free University of Berlin, Haderslebener
Str. 9, D-12163 Berlin, Germany The Auk 113(2):450-456,
1996
Indiana University
Interspecies Interaction: A Tool for the study of
Mimicry and Species-typical Birdsong Mariannne S.
Engle, Muskingum College Meredith J. West, Indiana
University
The
following article was presented at a recent International
Wildlife Rehabilitation Council conference in Portland,
Oregon. My appreciation and thanks to Ms Dolinsky
for permission to use it on this page.
Missing
a Crucial Step?
By MELISSA
B. DOLINSKY
Department
of Biology,
University
of Miami
Abstract:
The process of learning to sing in passerines is
not an instinctual behavior, but is instead learned
from their parents. Songbirds learn to sing in their
first 60 days. In a rehabilitation setting, songbirds
are missing this crucial part of their development.
Without the proper song development, songbirds are
unlikely to gain a territory, or to attract a mate.
BACKGROUND/DISCUSSION
Songbirds include those birds from the order Passeriformes,
commonly called passerines. There are approximately
5,400 different species of passerines. The suborder
Oscine includes those birds that we tend to think
of as your typical songbird, those birds that have
complex songs as adults. In the majority of Oscines,
the male is the one with the complex singing ability,
and there is much diversity among males of different
species in the length and complexity of their songs.
Song needs to be developed, just like any other
characteristic of songbird behavior. Singing the
correct song for that species is not an instinctual
process. The need to sing is instinctual, however
what song to sing has been found to be learned.
When and where young songbirds learn their songs
has long been studied. Just as songbirds differ
in their songs, they also differ in their song learning
process, though some basic principles seem to be
the same. Many species learn their song only during
the first few months, though a few can learn songs
their entire lives. Also differing between species
is from who the songs are learned, and how much
of the songs are accurately imitated (Liu & Kroodsma
1999).
Some species may exactly copy the songs they are
exposed to. On the other hand, many will not exactly
imitate the song or songs that they have been exposed
to. Instead they will take bits and pieces of it
and invent their own song, though usually similar
in construction to that which the species normally
sings.
There are several different types of songs that
I will be referring to. Learned songs are just that,
songs that have been learned from some source. There
are also isolate songs. When birds are raised without
hearing an adult of the same species, they tend
to develop this type of song. Isolate songs are
typically much simpler, and are composed of longer,
similarly pitched notes, than are the natural, learned
songs of the species.
REVIEW
The Basic Features of Song Learning –-
A
Case Study I am going to introduce the learning
process giving a case study and will then come back
later to go over specific aspects of the learning
process. The majority of research on this topic
has been on many of the native sparrow species.
For this case study we will be examining an experiment
carried out involving song sparrows.
Nine males were collected from the wild from four
different broods when they were around 4 to 6 days
old. They were raised by people until they were
weaned at 33 to 35 days old and then were placed
into individual wire-mesh cages. Live tutors were
used in this experiment. Four wild-caught adult
male song sparrows were used as the tutors. The
tutors were placed into flight aviaries and the
subject’s cages were placed adjacent to the aviaries,
so that they could have visual contact with one
of the tutors, while still being able to hear the
other three singing. Also, the subjects were rotated
so that their visual contact with one tutor varied
between the tutors. The subjects were there when
they were 33 to 94 days old, with the assumption
that their sensitive phase lay some time in this
time period.
When the subjects started singing the next spring,
their repertoires were analyzed. The average was
seven song types per subject. This does correspond
with birds raised exclusively in the wild by their
parents. Eight of the nine subjects learned songs
from two or more of the tutors and later imitated
these songs (Nordby et al. 2000).
In similar experiments in which some birds are exposed
to tutors and some are raised in isolation, those
birds that were exposed to tutors almost always
tend to imitate pieces and even complete songs.
Those birds raised in isolation always sang isolate
songs. These isolate songs were similar to each
other and consist of much more structurally simpler
songs than males raised with normal song exposure
(Nowicki et al. 1999).
Sensitive Learning Period
There
seems to be a specific time period in which songbirds
learn their songs. This “sensitive phase” is “when
an individual hears and is thought to acquire song
models” (Peters et al. 1992). Most species learn
their songs as juveniles. This learning period lasts
from around ten to sixty days of age. This learning
period corresponds very closely with the age at
which baby birds are in a rehabilitators care. The
songs that they are exposed to during this time
period are what they will learn from and start singing
once they mature. Songbirds do not start to sing
until the next spring, once they are around three
hundred days old. Once they start to sing, they
only imitate songs that they heard during their
early sensitive phase. Just a few passerines, such
as the European Starling, “are capable of learning
songs later in life” (Liu & Kroodsma 1999).
There is some controversy as to whether live tutoring
leads to a longer sensitive phase than does tape
tutoring. However, recent experiments show that
there is little to support this view. (Nelson 1998;
Catchpole & Slater 1995).
Live
Tutors versus Tape Tutors
Song learning has been taught successfully in the
lab in a variety of ways. The two most commonly
used teaching practices are by using a tape tutor
and the use of live tutors. Tape tutoring is playing
a recording of a song, or multiple songs over and
over. Live tutors are adult males of the same species
kept either in the same cage as the babies, or in
adjacent cages so that the young can both interact
with and hear the adults singing (Catchpole & Slater
1995).
Many species can learn songs equally well from either
taped songs or live tutors. Some species, however,
have had limited, if not zero success learning songs
from a tape and have only been recorded in lab learning
from live tutors. In addition, the age at which
learning occurs may differ from live to tape tutors.
This difference in learning success, however, may
have to do with how often the birds are exposed
to the tape versus the live tutor. If they are with
the live tutor all day long and he is singing all
day long, there will be much more exposure than
just hearing a taped song a few times during the
day (Nelson 1998).
Studies performed on hand reared chipping sparrows
and field sparrows have shown no learning from tape-recorded
songs. Instead their songs were highly abnormal
and were similar to babies raised without the benefit
of hearing any song whatsoever. When exposed to
live tutors, however, both species have been shown
to learn to properly sing (Liu & Kroodsma 1999).
Learning
From Limited Exposure to Tutors
The question now arises as to how often babies need
to be exposed to songs in order to learn them. Most
experiments “expose test subjects to hundreds or
even thousands of repetitions of tape-recorded song
models over the course of training” (Peters et al.
1992). There have been a few studies performed in
which babies were exposed to much less tutoring.
One study done on song sparrows showed that “song
sparrows are capable of learning from 30 repetitions
of a song type heard in a single 5-minute bout”
(Peters et al. 1992). The experiment was performed
on nine hand-raised song sparrows. The subjects
were raised out of auditory contact with other birds
until they reached 50days of age. This experiment
exposed song sparrows to taped songs varying from
over 1000 presentations of the song for a four week
time period, to 30 presentations of a song over
one five minute time period. Both groups learned
their songs equally well. Also, some of the most
successful learning experiments only played the
songs to the birds twice a day, once in the morning,
and once in the evening. Of course, one must keep
in mind that this experiment was only performed
on song sparrows, and the results may differ dramatically
in other songbird species.
How
Birds Learn
Since we have now gone over, what and when birds
learn, next we will go over how birds learn. Birds
exposed to songs of a different species do not start
imitating that song. Instead they seem to know to
only imitate songs coming from conspecifics. They
have the ability to discriminate between songs of
their own species and those of other species. Interestingly
enough, nestlings and fledglings even respond differently
when exposed to their song versus a song from another
species. In one experiment, “fledgling white-crowned
sparrows called more vigorously in response to playbacks
of songs containing conspecific phrases than to
playbacks of songs containing heterospecific phrases”
(Soha & Marler 2001). Somehow, babies are able to
discriminate between their song and others, even
prior to the sensitive phase of learning.
Research seems to suggest that there are specific
acoustic cues involved in the learning process.
These cues seem to be in the length, tone and pitch
of the introductory whistle of a song. In fact,
one group of researchers was able to get white-crowned
sparrows to successfully imitate heterospecific
songs, by just adding their introductory whistle.
Certain conspecific phrases are used as cues to
discriminate between conspecific and heterospecific
songs (Soha & Marler 2000; Soha & Marler 2001).
CONCLUSIONS
The significance of song learning may have several
implications for rehabilitators. Songbird vocalizations
are important socially in a variety of ways. Birds
that have not learned to sing will most likely never
be able to successfully attract a mate. In addition,
singing is essential when gaining a territory. Those
birds that are unable to correctly sing will not
be able to out-compete others for a territory. Without
a mate or a territory, we must ask ourselves how
normal of a life these birds will lead. Sure, they
are alive out in the wild thanks to us, but as rehabbers
isn’t it is our responsibility to teach our patients
to lead as normal a life as possible once they are
released and are on their own?
So, as rehabbers, what are some simple and affordable
solutions? Several methods may be used to help rehabilitated
babies learn to sing. Tape recordings of most songbirds
exist and are easily found for sale. These may be
purchased and then played to babies, especially
in the fledgling stage. My favorite method is using
the ‘Audubon stuffed animals’, those birds that
play back a real recording of a bird song. It is
very simple to keep a stuffed animal of that species
on top of a cage, and then play the stuffed animals
every time you are feeding that cageful of babies,
or every time you walk by. In addition to being
practical, these birds are also cute and visually
pleasing for any visiting members of the public,
and they are a wonderful way of distracting those
annoying kids that want to hold one of the cute
baby birds. Give them a stuffed animal to hold instead!
Also, most bird songs are easily found online at
sites such as the Cornell Lab of Ornithology site,
or at Enature.
You can also buy a portable, handheld birdsong player
called the BirdSong Identifier, made by For the
Birds. These come with cards that you insert.
Each card has 10 songs on it. One could easily play
these with one hand while feeding babies with the
other. The full set of songs and player is a bit
pricey and costs around $150 with the player alone
costing approximately $35. Playing recorded songs
will easily work for smaller rehabbers, however
for larger rehabilitation centers I’m not sure how
practical this would be. Also, tape recordings have
not been proven capable of teaching all songbird
species.
A more effective solution seems to be housing fledglings
with adult males of the same species. Baby songbirds
raised in this way have a much higher success in
learning to sing. They can also be housed in adjacent
cages, so that the babies can see the adults, and
of course house them adjacent so that the babies
can at the very least hear the adults. The highest
learning results have been in those situations in
which the baby birds have been housed in the same
cage as the adults. This subject definitely makes
the argument for keeping non-releasable songbirds
in order to use them as tutors.
While there is still much controversy surrounding
the different aspects of teaching songbirds to sing,
some aspects can be generalized. The process of
singing definitely appears to be a learned one and
is not instinctual for most songbirds. Also, there
is a specific period in which songbirds are open
to learning new songs. This appears to lie within
the first sixty days, though there is a lot of variation
between species. Rehabilitators have baby birds
in their care until they are around one and a half
to two months old. This almost exactly corresponds
with this sensitive learning phase. Rehabilitators
are currently sending songbirds out into the wild
without teaching them the crucial behavior of singing.
Without being able to attract a mate or gain a territory,
these birds will live a life of isolation. Also,
if none of our babies are contributing to the future
gene pool or population growth of the many declining
species, then raising songbird orphans will have
no conservation impact whatsoever.
ACKNOWLEDGEMENTS
Thank you so much to the University of Miami for
their support in this paper. Specifically, I would
like to thank Dr. William Searcy for his help in
finding materials and pointing me in the right direction
in finding information on this topic. I am also
very grateful to Dr. Ted Fleming for reviewing this
paper and for his helpful comments.
WORKS CITED
Catchpole, C. K. & Slater, P. B. J. 1995. How song
develops. In: Bird Song, pp. 45-69. Great Britain:
Cambridge University Press.
Liu, W. & Kroodsma, D. E. 1999. Song development
by chipping sparrows and field sparrows. Animal
Behaviour, 57, 1275-1286.
Nelson, D. A. 1998. External validity and experiment
design: the sensitive phase for song learning. Animal
Behaviour, 56, 487-491.
Nordby, J. C., Campbell, S. E., Burt, J. M. & Beecher,
M. D. 2000. Social Influences during song development
in the song sparrow: a laboratory experiment simulating
field conditions. Animal Behaviour, 59, 1187-1197.
Nowicki, S., Peters, S., Searcy, W. A. & Clayton,
C. 1999. The development of within-song type variation
in song sparrows. Animal Behaviour, 57, 1257-1264.
Peters, S., Marler, P. & Nowicki, S. 1992. Song
sparrows learn from limited exposure to song models.
Condor, 94, 1016-1019.
Soha, J. A. & Marler, P. 2000. A species-specific
acoustic cue for selective song learning in the
white-crowned sparrow. Animal Behaviour,
60, 297-306.
Soha,
J. A. & Marler, P. 2001. Cues for Early Discrimination
of conspecific song in the white-crowned sparrow
(Zonotrichia leucophrys). Ethology,
107, 813-826
|
