United States 

Department of 

Agriculture 

Forest Service 

Southern 

Research Station 

Research Note 

SRS-5 

A Mobile Aviary Design to 

Allow the Soft Release of 

Cavity Nesting Birds 

Kathleen E. Franzreb 

Abstract 

Translocation of endangered red-cockaded woodpeckers (Picoides 

borealis) has been an important component in restoration efforts to 

establish new populations and enlarge small populations. These 

efforts-relying on a "hard release" approach whereby the bird is captured, 

moved, and immediately released at the new site-have met with mixed 

results. A mobile aviary has been designed with the expectation of 

improving translocation success for red-cockaded woodpeckers that also 

can be used for other cavity nesting birds with depleted populations. The 

mobile aviary allows a "soft" release, in which the bird is moved to the 

release site and maintained there for a given period of time prior to 

release. While in the aviary, the individual can become accustomed to the 

release area, thus increasing the likelihood that it will remain there once 

released. The aviary consists of a circular metal frame, approximately 5.1 

meters (m) high and 4.7 m in diameter, with hardware and shade cloth on 

the outside. It encompasses a living pine tree with a natural or artificial 

cavity in the trunk, to be used by the bird for nightly roosting. It has 

proved to be relatively inexpensive to construct, easily moved, and 

durable under a range of weather conditions. An evaluation of the mobile 

aviary in terms of increasing translocation success for the red-cockaded 

woodpecker is underway at the Savannah River Site in South Carolina. 

Keywords: Cavity nesters, endangered birds, mobile aviary, redcockaded woodpecker. 

Introduction 

Releasing animals into the wild (translocating) is a widely 

accepted strategy for reestablishing extirpated wildlife 

populations or augmenting depleted ones. Wildlife 

professionals succeeded in translocating individuals of a 

number of species that had been propagated in captivity, 

including American bison (Bison bison), bald eagle 

(Haliaeetus leucocephalus), peregrine falcon (Falco 

peregriraus), and bean goose (Anserfabalis) (Beck and 

others 1994) as well as species captured in the wild: wild 

turkey (Meleagris gallopavo), bighorn sheep Qvis 

canadensis), and elk (Cervus elaphus) (Griffin and others 

Kathleen E. Franzreb, Project Leader, Southern Research Station, U.S. 

Department of Agriculture, Forest Service, Clemson, SC 29634-1003. 

September 199'7 

1989, Wolf and others 1996). Although translocation efforts 

have emphasized game species, some conservation 

strategies have entailed releasing individuals of endangered 

species as well, within either their historical or their current 

range. 

Wolf and others (1 996) surveyed 336 of the 4 13 known 

translocation programs in North America, Australia, and 

New Zealand. Of these, 89 involved endangered, 

threatened, or sensitive species and achieved an average 

success rate of 53 percent. Included in the survey was the 

endangered red-cockaded woodpecker (Picoides borealis) 

(RCW. 

The RCW, a territorial species endemic to open pine 

woodlands of the Southeast, is nonmigratory and a 

cooperative breeder (Lennartz and others 1987, Walters and 

others 1988). These birds construct cavities in living pine 

trees for nightly roosting throughout the year and for nesting 

during the breeding season. Recovery has focused on 

increasing population size and reestablishing birds in 

abandoned habitat. Translocation has been a tool for 

minimizing the loss of genetic diversity in small populations 

and for facilitating population recovery after a catastrophic 

event. The results of these translocations have been mixed 

(Allen and others 1993, Costa and Kennedy 1994, DeFazio 

and others 1987, Odum 1983, Reinman 1995, Rudolph and 

others 1992). Of the 143 RCW translocations from 1989 to 

1994, the success rate was 62 percent for females, 42 

percent for males, and 33 percent for pairs (Costa and 

Kennedy 1994). All RCW translocations and more than 

two-thirds of those summarized by Wolf and others (1996) 

have involved "hard" releases: capturing the bird, 

transporting it to the release site, and then immediately 

releasing it. 

Since 1986, the RCW population at the Savannah River Site 

in South Carolina has been in a recovery program (Allen 
Figure I-Diagram of mobile aviary designed for the red-cockaded woodpecker and other cavity nesting birds. 

and others 1993, Franzreb 1997). Increasing the probabiliq 

of successfully moving these birds would have a beneficial 

effect on their recovey. With the expectation of improving 

translocation success, an aviary was designed for RCW that 

provides access to a cavity while allowing confinement to 

the release site for a specified period of time. During this 

time the captive bird receives food, water, shelter, and 

careful monitoring. This method is known as a "soft" 

release. Keeping the bird in captivity at the release site may 

strengthen its potential to develop an affinity for the site and 

may increase its inclination to remain at the site after 

release. To be effective the aviq had to be mobile, simple 

to take down and reassemble, relatively inexpensive to 

consmct, and able to withstand normal weather conditions. 

This study consists of three phases: (1) designing, 

constaucting, and testing the aviary for durability; 

(2) testing the aviary to determine whether an RCW could 

be successfully maintained in it; and (3) detemhing 

whether the aviary can irrstill in the bird an attachnnent for 

its release site so that relocation efforts are more productive. 

This paper repofis on phase I results. 
Materials and Methods 

Study Area 

The aviaries were tested at two South Carolina locations; 

one near CLemson University and the other at the Savannah 

River Site, a U.S. Depament of Energy nuclear production 

facility near Aiken, SC. 

Mobile Aviary Design 

The mobile aviary consists of four circular aluminum hoops, 

each bolted together and connected to the others with 

aluminum braces (fig. 1). The four hoops form a structure 

measuring approximately 3.5 m in height and are covered 

with a 0.27-m mesh hardware cloth. A smaller hoop is 

bolted to the structure with connecting braces, forming an 

upper section. Shade cloth covers this upper section; it is 

tightly affixed to the tree trunk with a rachet strap. The 

lowest hoop has a smali door to allow access to the inside of 

the aviary. Wen all sections are in place, the overall height 

is approximately 5.1 m. The aluminum frame is erected 

from the ground upward around a living pine tree that 

contains an artificial (Allen 199 1) or natural RCW cavity 

about 4 rn or less from the ground. The site must be 

relatively flat and the tree relatively straight, with dead 

limbs removed to prevent subsequent damage to the aviary 

from falling branches. 

To assess the aviary's durability under various weather 

conditions, five field tests were carried out between October 

1993 and March 1995, each lasting at least 2 weeks. The 

materials to construct the aviary, including the frame and 

shade cloth, cost about $1,000. Its components fit into a 

standard-sized pickup truck or small trailer. Two people 

can assemble the aviary at the release site in about 1-2 days, 

allowing it to be used repeatedly. 

Results and Discussion 

During the field tests, the aviary withstood high winds and 

heavy rain and required no repairs after the testing periods. 

Based on durabiliy, ease of assembly, and cost of 

conshuction, the aviary is considered to be an effective tool 

for confining RCW's at the release site. 

One of the major goals of the RCW recovery efforl is to 

restore depleted populations, including the reintroduction of 

bird pairs. The mobile aviav has the potential to increase 

the success of b.anslocations into populations that are 

critically small, and to restore populations in areas where 

the species has been extirpated. For it to be a viable 

management tool, the aviary must be used in relocation sites 

that provide suitable, good-quality habitat. Ensuring good 

habitat quality may require installing artificial cavities, 

controlling hardwood midstory vegetation in clusters of 

trees that contain the cavities, minimizing cavity use by 

competitors, and providing quality foraging. 

The mobile aviary has proven itself in terms of its design 

and its serviceability in the field. The next phase entails 

maintaining the birds in the aviary and determining whether 

2 to 4 weeks of confinement will increase the probability 

that they will remain at the site once released. Field tests 

are underway to determine whether the mobile aviary 

increases the effectiveness of relocation efforts. If these 

prove successful, the consequences to the recovery of 

RCW's and other endangered or threatened avian species 

could be far-reaching. 

Acknowledgments 

This research was funded by the U.S. Department of 

Energy, Savannah River Site, and its cooperation is 

gratefully acknowledged. The author is indebted to C. 

Dachelet, D. Ussery, P. Johnston, K. Laves, J. Brucke, and 

J. Edwards for their technical support during field tests and 

to the staff of the Savannah River Forest Station for their 

longstanding support of this project. We thank Clemson 

University for donating the metal frame (which was 

modified) that was originally used in a study of ozone and 

acid rain funded by the National Acid Precipitation 

Assesment Program. For providing advice and/or 

manuscript review, the author thanks D.C. Rudolph, 

J. Reinman, J. M. Scott, R.G. Hooper, C. Dachelet, and 

R. Costa. 

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