The Appropriateness of Puppet-Rearing Birds
for Reintroduction
LAURA L. VALUTIS*‡ AND JOHN M. MARZLUFF†
*1910 University Drive, Raptor Research Center, Boise State University, Boise, ID 83725, U.S.A.
†Sustainable Ecosystems Institute, 30 E. Franklin Road, Suite 50, Meridian, ID 83642, U.S.A.
Abstract: Captive propagation and reintroduction programs for rare and endangered species rarely include
testing of techniques prior to initiation of recovery efforts. To experimentally test the effects of rearing social,
altricial birds with or without a conspecific, parental model (a puppet), we used Common Ravens (Corvus corax) in southwestern Idaho as surrogates for the endangered Hawaiian Crow (Corvus hawaiiensis) and Mariana Crow (Corvus kubaryi). A puppet is believed to reduce sexual and filial imprinting on human caretakers.
We raised 49 ravens without a puppet and 25 ravens with a puppet. We initiated puppet-rearing when birds
were 7 days of age and continued until 60 days of age, when nestlings could eat well on their own. The influence of puppet-rearing was tested as part of a factorial design that also tested for the effects of conspecific tutoring and age at release. Rearing ravens with a puppet did not affect social behaviors prior to release, dispersal
from the release area, or integration with wild birds after release. Ravens raised with a puppet, however,
were more fearful of caretakers and more vigilant prior to release, characteristics that may have improved
their chances for survival after release. It is important for researchers to consider the species and the desired
pre- and post-release behaviors to determine if rearing with a puppet is appropriate for their recovery efforts.
These considerations can be taken into account by using a surrogate species prior to recovery efforts and creative management approaches in the initial phases of an endangered species recovery program.
Conveniencia de la Cría de Aves con Títeres para Reintroducción
Resumen: La propagación en cautiverio y los programas de reintroducción de especies raras y amenazadas
raramente prueba las técnicas antes de iniciar los esfuerzos de recuperación. para probar experimentalmente los efectos de la cría social, aves altriciales con o sin un modelo parental (un títere) coespecífico, utilizamos el cuervo común (Corvus corax) en el suroeste de Idaho como sucedáneo del cuervo de Hawaii
amenazado (Corvus hawaiiensis) y el cuervo mariana (Corvus kubaryi). Se considera que los títeres reducen
la influencia sexual y filial para con los cuidadores humanos. Criamos 49 cuervos sin títeres y 25 con un títere. Iniciamos la cría con títere a los 7 días de edad y continuamos hasta los 60 días de edad, cuando los polluelos pueden comer por su cuenta. La influencia de la cría con títere fue evaluada como parte de un diseño
factorial que también evaluaba los efectos de la enseñanza por coespecíficos y la edad de liberación. La cría
de cuervos con títeres no afectó las conductas sociales anteriores a la liberación, la dispersión del área de liberación o integración con aves silvestres después de la liberación. Sin embargo, los cuervos criados con títeres
fueron mas temerosos de los cuidadores y mas vigilantes antes de la liberación. Estas características pueden
mejorar la supervivencia después de la liberación. Es importante para los investigadores el considerar las especies y las conductas deseadas pre- y post-liberación para determinar si la crianza con títeres es apropiada
para sus esfuerzos de recuperación. Estas consideraciones pueden ser tomadas en cuenta utilizando especies
sucedáneas antes de los esfuerzos de recuperación y mediante aproximaciones de manejo creativas en las
fases iniciales de un programa de recuperación de especies amenazadas.
‡Current address: The Nature Conservancy, 2404 Bank Drive, Suite 314, Boise, ID 83705, U.S.A., email lvalutis@tnc.org
Paper submitted November 3, 1997; revised manuscript accepted September 16, 1998.
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Introduction
It is often difficult to test new conservation methods
with rare species because sample sizes are small and
knowledge of the species’ life history may be limited
(Scott & Carpenter 1987; Wallace & Temple 1987; Griffith et al. 1989; Kleiman et al. 1994; Tear et al. 1995). An
example of a rarely tested method is the use of puppets
to reduce imprinting in young birds hand-reared for later
reintroductions. Puppet-rearing uses a conspecific, parental model (puppet) to reduce sexual and filial imprinting on human caretakers (Cade & Fyfe 1977; Wallace 1994). In many birds, filial or following-response
imprinting occurs at a young age and can occur on a different object or species, compared with sexual imprinting, which occurs during the juvenile phase (O’Conner
1984). In other words, a bird could be filially imprinted
to its caretaker but sexually imprinted to the correct
species if exposed to conspecifics during the juvenile
phase (Hess 1973; Powell 1992). Therefore, puppet-rearing, which is performed during the nestling phase, may
be irrelevant to sexual imprinting in some species. Although correct sexual imprinting is critical to a successful reintroduction program, correct filial imprinting may
or may not affect the success of reintroductions.
Hand-rearing birds in captivity is commonly used to facilitate restoration because removing multiple clutches
from wild pairs can increase the productivity of each pair
by allowing caretakers to rear the initial broods in captivity and wild adults to rear subsequent broods (Wallace &
Temple 1983; Powell & Cuthbert 1993; Wood & Collopy
1993). Once the decision has been made to use handrearing, caretakers must decide if they will rear young
with or without a puppet. There are both negative and
positive aspects of rearing birds with a puppet. Puppetrearing may be important for proper sexual imprinting if
birds cannot be raised with conspecifics. Raising birds
with a puppet, however, is labor-intensive and costly
(Wallace 1994). In addition, there may be benefits to having captive-reared birds filially imprinted on the caretakers, depending upon the species and the desired postrelease behavior of the birds (Erickson & Carpenter 1983;
Wallace & Temple 1987). For example, if the birds must
be observed or handled frequently for medical reasons,
handling may be less stressful on the birds if they are filially imprinted and not fearful of the caretakers.
Experimental assessments of the effects of puppetrearing on endangered species are lacking, but a surrogate species—a common, taxonomically similar species
with an ecology similar to that of the rare species—
could be used to experimentally test the effectiveness of
such techniques (Scott & Carpenter 1987; Horwich
1989; Beck et al. 1994; Louda 1994). We used Common
Ravens (Corvus corax) as surrogates to experimentally
test the importance of puppet-rearing to the recovery of
the critically endangered Hawaiian Crow (Corvus ha-
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585
waiiensis) and Mariana Crow (Corvus kubaryi). Common Ravens are taxonomically similar to these rare
crows (Duckworth et al. 1992), and they are long-lived
and social, with an extended period of post-fledging parental dependency (Skarphedinsson et al. 1990) similar
to that of Hawaiian and Mariana Crows (Munro 1960;
Tomback 1986). The objective of our study was to experimentally test the effects on behavior and survival after release of hand-raising altricial, social birds with or
without puppet models.
Methods
Experimental Design
We collected entire clutches of eggs from wild pairs of
Common Ravens and reintroduced captive-reared ravens
within and surrounding the Snake River Birds of Prey National Conservation Area of southwestern Idaho (Engel &
Young 1992).
We fed chicks within the first hour after hatching (details of incubation and feeding regimes given by Whitmore and Marzluff [1998]). Before their eyes opened,
from hatching until 7 days of age, all raven chicks were
handled 7–12 times throughout the day for weighing,
feeding, maintenance, and cleaning.
When raven chicks were 7–10 days old we randomly
assigned them to be fed with or without a puppet. Caretakers fed birds raised without a puppet with forceps
and allowed them full visual and vocal contact with caretakers. Caretakers fed puppet-reared ravens with a hand
puppet that was modeled from an adult raven and
placed behind a curtain to minimize human contact. To
elicit a feeding response, we attempted to imitate a parent raven by intermittently and conspicuously moving
the puppet and imitating vocalizations characteristic of
adult ravens tending young (O’Conner 1984). All birds
were randomly assigned to be reared with conspecific
broodmates of similar ages (2–4 individuals per nest
bowl). The room with the puppet-reared ravens held no
more than four nest bowls (8–16 individuals). The puppet-reared ravens saw humans once in the morning
when chicks were weighed and again in the evening
when the room was cleaned, but never during feedings.
When ravens were approximately 30 days old we
moved them to pre-fledging aviaries (3 3 4 m). Ravens
raised without a puppet were fed directly by caretakers,
whereas puppet-reared ravens were housed in a separate aviary covered on three sides to prevent visual contact with caretakers and fed with a puppet through a
sliding wooden door. Ravens were isolated from humans until they could eat on their own and fly between
perches. Once this occurred (at approximately 60 days
of age), we concluded puppet-rearing and moved all
captive-reared ravens to a larger flight aviary.
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Ravens were held at these flight aviaries until they
were moved to the release sites in either July or October. While in the flight aviary, ravens were exposed to
caretakers once each day when food items and fresh water were provided and twice each month during medical
screenings.
When captive-reared ravens were ready for release (release at fledging at 90.1 6 2.7 days of age and release at
post-fledging at 185 6 1.8 days of age), we transported
them to release sites in a 0.3 3 0.5 m carrying kennel.
The release site consisted of a protective 1 3 1 m
wooden box (1.5 m above the ground) inside a 6 3 6 m
aviary. The aviary was made of a flexible 2.5-cm mesh
netting attached to the top of a 2-m-high chain-link fence
and supported by a 3-m center pole and several perches.
We attached chicken wire to the bottom of the fence
and extended it outward 0.5 m to prevent potential
predators from digging under the fence. We acclimated
ravens to the release site for 3 weeks prior to release.
We used four measures of behavior to quantify the effects of puppet-rearing on Common Ravens: (1) fear response to caretakers prior to release, (2) time-activity
budgets at the release site, (3) timing of dispersal from
the release area, and (4) survival through 1 year after release. Because of the short duration of the study, we
were unable to determine the effects on sexual imprinting of rearing a Common Raven with or without a puppet. In conjunction with testing the effects of raising
ravens with or without a puppet, we randomly assigned
ravens to be raised with or without a wild, older conspecific (tutor) and released at fledge-age in July and August
or post fledge-age in October and November (Valutis
1997). Thus, we used a three-factor factorial design,
with puppet-rearing, tutoring, and age at release as the
factors of interest.
Data Analysis
To understand the effects of puppet-rearing, we first appraised the significance of the three-way and two-way
interactions among puppet-rearing, tutoring, and age at
release in all analyses before testing the main effect of
puppet-rearing. The only significant interactions were
between puppet-rearing and age at release for behaviors
measured prior to release. Therefore, to appraise the influence of puppet-rearing for all pre-release behaviors,
we examined this two-way interaction; for all postrelease behaviors, we examined the main effect of raising a raven with a puppet.
A raven’s behavior at a release site could influence the
behavior of another raven at that site. Therefore, to
avoid pseudoreplication, we used the release site instead of individual ravens as the experimental unit in
most analyses (Hurlbert 1984). Because ravens are
known to show individual variation in skills and behaviors (Heinrich 1995) and because birds from the same
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Valutis & Marzluff
releases were rarely observed in the same flock after dispersal from the release area, we tested the appropriateness of using the individual (instead of the release site)
as the experimental unit for post-dispersal survival. Use
of the individual as the experimental unit is appropriate
when within-release site variation is not significantly
larger than between-release site variation. To assess this,
we used a nested analysis of variance (ANOVA) (SAS Institute 1994). We found that among-release site variation
of post-dispersal survival was not significantly larger
than within-release site variation (F(13,43) 5 1.18, p 5
0.32). Therefore, we used the individual as the experimental unit for post-dispersal survival and the release
site as the experimental unit for all other analyses. Results are presented as adjusted least-square means ( x 6
SE). Significance level is #0.05 for all analyses unless
otherwise stated.
Fear Response to Caretakers
In ravens, fear response begins at 14 days of age (Stiehl
1978). We documented filial imprinting of all captivereared ravens to caretakers at the release site by recording the reaction of each bird to caretakers when food
and water were delivered daily. If a bird flew from or actively avoided the caretaker, we considered this a fearful
response and recorded it as 1. If a bird begged or approached the caretaker, we considered this an affinity
response and recorded it as a 0. We tallied fear responses and divided the sum of the individual scores by
the number of provisioning visits (n 5 21) made to the
release site to obtain an average fear score for each
group of birds at a release site (the release group). We
used a nested ANOVA (individual birds nested within
the release; SAS Institute 1994) to examine the interactions and main effects of puppet-rearing, tutoring, and
age at release.
Time Budget
We conducted 10 focal observations on individual birds
on separate days while they were held at the release site
to determine behavioral time budgets at each release site.
We observed individual ravens at the release site for
15-minute periods. To unit-sum constraints, we analyzed
only two behavioral categories: social behaviors, including fighting, displacements, allopreening or preening another, allobilling or softly preening another’s bill, aggressive allopreening or allobilling, and object chase with
another, object tug-o-war with another and vigilant behaviors, including perch alert in which the bird’s head and
neck were extended upward and alarm vocalizations. We
calculated the mean percentage of time birds spent in
each behavioral category. We transformed these percentages by taking the arcsine of the square root to increase
the normality of the data distribution (Zar 1984). We com-
Valutis & Marzluff
pared time spent in social and vigilant behaviors using a
multivariate analysis of variance (Systat 1993). The number of individuals at a release site was used as a covariate,
with puppet-rearing, tutoring, and age at release as the
three independent variables. When interpreting the significance of the univariate results for the independent
variables for this analysis, we used a Bonferroni adjusted
alpha (0.025) to control experiment-wise Type I error.
Dispersal
To document dispersal from the release site, we
equipped all ravens with radio transmitters mounted on
backpacks made of teflon ribbon 1 week prior to release
(Buehler et al. 1991; Vekasy et al. 1996). Transmitters
and backpacks weighed 22–25 g (less than 3% of a bird’s
body mass) and were designed to last 1000 days (Advanced Telemetry Systems). Ravens were individually
marked by a colored transmitter antenna, a U.S. Fish and
Wildlife Service band on the right leg, and a unique alpha numeric colored legband on the left leg.
From 1975 to 1995, 820 wild, parent-reared ravens
were banded as nestlings within the Snake River Birds of
Prey National Conservation Area (U.S. Geological Survey, Snake River Field Station, unpublished data). We
compared dispersal distances and causes of mortality between these wild juveniles and hand-reared ravens.
From 1993 to 1995 we also placed radio transmitters on
11 wild nestlings from three nests to determine survival
rates.
We considered a bird to have dispersed from the release area if it did not return to the release site for provisioned food or water for 1 week. We confirmed independence when we found the bird at a roost site or foraging
area with conspecifics. We used the number of days from
release until dispersal as a measure of independence from
the release site. We used a nested ANOVA (individual
birds nested within the release group) to investigate the
interactions and main effects of puppet-rearing, tutoring,
and age at release, with the number of days to disperse
from the release area as the dependent variable.
Survival
We determined post-dispersal survival through the first
year after dispersal by using individual birds as the experimental unit. We excluded eight birds from the analysis because we were unable to monitor them beyond 2 days
after dispersal and we were not certain if they died, experienced radio failure, or integrated into natural flocks and
dispersed from the study area. We also excluded two
birds that died at the release site before dispersal. We normalized the data prior to analysis using arcsine transformation (Zar 1984).
We first compared post-dispersal survival of birds
raised with versus without a puppet using a log-linear
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587
model (StatSoft 1995). This allowed us to categorize survival after dispersal and to test for any interactions of
puppet-rearing, tutoring, and age at release before examining the main effect of puppet-rearing (Zar 1984). We
categorized the survival status of each individual after release as (1) dead if we located the individual and assigned cause of death; (2) unknown if we located the individual within the study area 2–59 days after dispersal
but never found the bird again; or (3) alive if we located
the individual within the study area 60–365 days after
dispersal. We chose 60 days as the point at which to distinguish between unknown and alive status because this
is when the survival curves leveled off. We lost contact
with birds for three possible reasons. First, the birds may
have remained in the area with failed transmitters. This is
unlikely, because when we observed the ravens after release, as part of another study, none had malfunctioning
transmitters. Second, the birds’ transmitters may have
failed as a result of a predation event after release. This is
possible because we found one dead crow that had been
shot and its transmitter damaged. Third, the birds may
have emigrated from the study area. This is the most likely
scenario because ravens quickly integrated with wild conspecifics at roost areas, and juvenile ravens have been
known to disperse long distances during the first years of
life (Heinrich et al. 1994; Ratcliff 1997).
We used survival-curve analysis (StatSoft 1995), with
the number of days survived from day of dispersal as the
dependent variable. Survival-curve analysis controlled
for censored observations (n 5 8; when we did not
know the exact survival times for each individual or
when individuals survived until the end of the study; Lee
1980). First, we used a multiple-sample survival analysis
to test the three-way and two-way interactions among independent variables (puppet-rearing, tutoring, and age
at release). Because there were no significant interactions (all p values were .0.27), we used the KaplanMeier procedure to test the main effect of puppet-rearing (Pollock et al. 1989). This allowed us to set outer
bounds for survival by classifying birds of unknown status as either dead (a complete observation) or alive (a
censored observation). We used Cox’s F test to analyze
these results because it is more sensitive to small sample
size and exponential survival distributions than Gehan’s
generalized Wilcoxon test (Lee 1980).
Results
We hand-reared and released 74 ravens at 21 releases from
June 1993 through November 1995. Eight of these releases contained 25 puppet-reared ravens (2–5 individuals/
site), and 13 releases contained 49 ravens raised without
a puppet (2–6 individuals/site).
Puppet-rearing and age at release significantly interacted to influence pre-release behaviors. Raising a raven
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Puppet-Rearing Birds
without a puppet and releasing it at fledge age significantly decreased its fear response to caretakers (F(1,13) 5
4.89, p 5 0.05; Fig. 1a). All other hand-rearing and release regimes produced ravens that were fearful of caretakers prior to release.
Raising a raven with a puppet and releasing it after
fledge age tended to decrease the percentage of time it
spent vigilant (Wilks’ Lambda F(3,8) 5 0.573, p 5 0.65;
Univariate F(1,10) 5 4.89, p 5 0.049; Bonferroni adjusted
alpha was p 5 0.025; Fig 1b). Raising a raven with a puppet
did not significantly increase the amount of time it spent
performing social behaviors relative to the amount spent
by birds reared without a puppet (with puppet n 5 8, x 5
14.2 6 1.5%; without a puppet n 5 11, x 5 11.7 6 1.4%;
F(1,10) 5 1.42, p 5 0.26).
Valutis & Marzluff
Dispersal
Birds raised with and without a puppet dispersed from
the release area after a similar amount of time (raised
with a puppet, n 5 8, x 5 6.7 6 1.9 days; raised without a puppet, n 5 13, x 5 9.4 6 1.9 days; F(1,13) 5 1.11,
p 5 0.31). Most hand-reared ravens, regardless of puppet-rearing, quickly integrated with wild ravens once
they dispersed from the release area ( x 5 3.8 6 1.7
days; n 5 64 ravens). One puppet-reared raven, however, dispersed 3 km away the day of release and joined
three other captive-reared ravens at their release site.
This raven remained with the other ravens for 11 days
before integrating with wild ravens. Another raven
reared with a puppet did not disperse from the release
area until 137 days after release. This raven, which always had been fearful of caretakers prior to release (fear
response score, x 5 1.0), remained alone at the release
site for 6 months, and 32 days after release began to fly
out to meet the caretakers when they provisioned food.
After dispersal we located hand-reared ravens within
the study area up to 70 km from their release site. To
date, no ravens have been recovered outside of the
study area. Wild ravens within the National Conservation Area have dispersed large distances (up to 434 km
from the nest area; U.S. Geological Survey, Snake River
Field Station, unpublished data), and we suspect that
many hand-reared ravens moved outside the study area.
Survival
Figure 1. Fear response of Common Ravens reared
with or without a puppet and released at fledge or
post-fledge age (a). Percentage of time spent vigilant
by Common Ravens reared with or without a puppet
and released at fledge age or post-fledge age (b). Standard error and sample sizes are provided above the
bars.
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Volume 13, No. 3, June 1999
Of the 74 captive-reared ravens released from 1993 to
1995, only 2 (2.7%) died at the release site prior to dispersal. These birds were preyed upon by Golden Eagles,
(Aquila chrysaetos) at 13 and 17 days after release. Both
ravens were raised without a puppet and displayed low
levels of fear toward caretakers (fear ratings of 0.41 and
0.53, respectively). Raising a raven with a puppet (n 5
8, x 5 89.9 6 4.1%) or without a puppet (n 5 13, x 5
85.4 6 3.5%) did not affect the percentage of birds surviving from release to dispersal (F(1,12) 5 0.62, p 5 0.45).
Hand-reared ravens died from causes similar to those
of wild nestlings with patagial tags and transmitters; for
example, raptors accounted for most of the known predation events in both hand-reared and wild ravens. Of 72
hand-reared ravens that survived to disperse from the release area, 15 (20.8%) died within the study area between 1 and 165 days after dispersal ( x 5 33.1 6 12.0
days after dispersal—similar to wild, radio-tagged nestlings; n 5 5, x 5 9.2 6 3.8 days after fledge; T(18) 5
1.13, p 5 0.28).
Of the 72 ravens that survived to disperse from the release area, 49 (68.1%) were found alive within the study
area from 3 to 571 days after dispersal. Of these, 25
(51%) remained in the study area at least 2 months after
their release and were consistently observed alive ( x 5
Valutis & Marzluff
Puppet-Rearing Birds
589
448.2 6 18.4 days of age). The other 24 (49%) were not
found beyond 59 days after release; they either emigrated or died with malfunctioning transmitters. These
ravens averaged 178.1 6 17.3 days of age when we last
located them within the study area. If we assume that
these ravens of unknown status died, then raising a
raven with a puppet marginally improved post-dispersal
survival (G2(2) 5 5.11, p 5 0.08). If we assume that
ravens of unknown status were alive outside of the study
area, raising a raven with a puppet significantly improved post-dispersal survival (G2(2) 5 6.63, p 5 0.03).
We found 9 (12.5%) captive-reared ravens within the
study area 1 year after they dispersed from the release
area. Eight of these were raised without a puppet,
whereas only 1 raven had been raised with a puppet.
Survival analysis confirmed the trend for ravens raised
with a puppet to have higher post-dispersal survival than
ravens raised without a puppet. Analysis of survivorship
curves complimented the categorical analysis of survivorship and allowed us to censor individuals from analysis if their status became unknown. If we assume that
ravens with unknown status were alive outside the study
area, there was a tendency for ravens raised with a puppet to show improved survival (F(26,4) 5 4.19, p 5 0.09;
Fig. 2a). If we assume that ravens with unknown status
were dead, there was no significant increase in survival
for ravens raised with a puppet (F(56,28) 5 1.21, p 5
0.29; Fig. 2b).
Discussion
Raising birds with a model puppet has been used in
many captive propagation and reintroduction programs
(Cade & Fyfe 1977; Horwich 1989; Kuehler et al. 1994).
Our goal was to determine if puppet-rearing affected behavior and if these changes in behavior affected the success of reintroduction.
Raising ravens with a puppet did not increase the percentage of time the ravens performed social behaviors
prior to release, and ravens reared with a puppet did not
disperse from the release area sooner than ravens raised
without a puppet. Ravens raised with and without a
puppet quickly integrated with wild conspecifics at
roost areas and presumably dispersed long distances
(Heinrich et al. 1994; Ratcliff 1997). Ravens reared with
a puppet, however, were more fearful of human caretakers than ravens reared without a puppet. These effects
on behavior may have translated to changes in survival
of captive-reared young. For example, ravens raised
without a puppet tended to have lower post-dispersal
survival. We estimated their actual post-dispersal survival by bracketing survival based upon whether we assumed ravens of unknown status were dead or alive. Juvenile ravens are known to join large social groups in
the fall and travel widely throughout their first several
Figure 2. Survival curve of Common Ravens reared
with or without a puppet. Birds were classified as dead
after release (a complete observation), alive when we
located the individual within the study area 60–365
days after release (a censored observation), or unknown when we were unable to locate the individual
.60 days after release because of transmitter failure,
dispersal from the study area, or other unknown factors. This unknown status was difficult to interpret because we could not calculate survival for birds of unknown status. Therefore, we had to assume that these
birds were still alive (a) or had died after release (b).
years before they reach sexual and social maturity (Heinrich et al. 1994; Ratcliff 1997). This juvenile dispersal
and integration period may explain why we had such a
large number (30.4%) of unknown-status birds once
they integrated with wild conspecifics. Therefore, it is
likely that rearing a raven with a puppet tended to improve post-dispersal survival.
Because ravens do not reproduce until their second to
fourth year (Skarphedinsson et al. 1990), we were unable to confirm breeding activity in any of the handreared ravens. In a companion study, however, we
raised and released 30 Black-billed Magpies (Pica pica)
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and 57 American Crows (Corvus brachyrhynchos) without puppets and later observed 3 of these breeding.
Thus, raising corvids with a puppet is not essential for
correct sexual imprinting if they are raised in conspecific groups. If birds must be raised alone, without access to broodmates or conspecifics, we recommend that
they be raised with a puppet to avoid inappropriate sexual imprinting. Lorenz (1981) reported that hand-reared
ravens would mate with conspecifics and display little
fear of humans as long as they were exposed to a conspecific at the juvenile stage. Other studies (Hess 1973;
Cade & Fyfe 1977; Powell 1992) have demonstrated that
when chicks are reared with several groups of broodmates in close proximity, inappropriate sexual imprinting is not a concern.
It appears that filial behavior can be modified by rearing some birds without a puppet and that this does not
compromise social imprinting. Therefore, there may be
situations in which puppet-rearing is not necessary for a
successful reintroduction. Producing less fearful birds
by raising them without a puppet may be beneficial if
the birds must be handled frequently in order to detect
the onset of disease or abnormal growth, or if stress is a
concern in a captive propagation program (Erickson &
Carpenter 1983). In addition, raising birds with a puppet
is costly in terms of time and resources (Wallace 1994).
If staff or funds are limited, it may be difficult for caretakers to provide quality care for birds reared with a
puppet.
We suggest that captive propagation programs be conducted with an adaptive management approach (Walters
1986) to reintroduction efforts. In the initial years of a
program, researchers should rear some birds with and
some without a puppet to compare post-dispersal behavior and survival, because every species reacts differently in different environments. Kleiman (1996) argued
that the most successful reintroduction programs release large numbers of animals at several releases. If
caretakers can rear more individuals without a puppet
than with a puppet, and if experiments show that puppet-rearing may not yield a significant difference, then it
should not be done. For example, suppose researchers
found that raising birds with a puppet improved postdispersal survival (i.e., quality) but could release more
birds if they did not use a puppet (i.e., quantity). If quality divided by quantity .1, then caretakers should continue to raise birds with a puppet.
The decision to raise a bird with or without a puppet
should be based upon the species, its sociality, the number of birds that can be raised, and the desired response
to caretakers. Birds that are precocial, with a short parental dependency period and low offspring survivorship, may require puppet-rearing to avoid inappropriate
imprinting. On the other hand, birds that are altricial,
with an extended parental dependency period, higher
offspring survival, and extended social development,
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Valutis & Marzluff
may not require strict human isolation if they can be
reared with conspecific broodmates.
Before a captive propagation and reintroduction program is initiated, it is important to consider the life history
of the species and the desired post-release results. Although puppet-rearing may have improved post-dispersal
survival, the birds did not remain nearby during the juvenile stage. This dispersal or wandering behavior may be
beneficial if it is important for reintroduced birds to integrate with wild conspecifics. But if it is more important
for reintroduced birds to remain closer to the release
area, then they should not be reared with a puppet. To
understand these post-release behaviors, researchers
should consider the use of adaptive management techniques by testing various hand-rearing methods with a
suitable surrogate species prior to recovery and with the
endangered species at the onset of the recovery program.
Acknowledgments
This research was supported by the U. S. Fish and Wildlife
Service (grant 14–48–0001–94523), the Chicago Zoological Society, Kaytee Products, Inc., and private donations
to the Conservation Research Foundation and Sustainable
Ecosystems Institute. In particular we thank J. Zamzow,
R. Lopez, the Boise Co-op, and Darling International for
donations, and K. Whitmore, C. Landon, J. Barrett, L.
Schueck, E. Zellers, and G. Saathoff for their hard work
and dedication. M. Pavelka, P. Harrity, C. Kuehler, and B.
Telford were instrumental in getting this project off the
ground in 1993. J. Munger, J. Belthoff, L. Bond, J. Bart,
and L. Schueck helped with analyses and review.
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