The Puerto Rican Parrot Genetic Assessment of the Captive Breeding Program

Abstract

The Puerto Rican parrot Amazona
vittata is one of the most critically
endangered birds in the world. Historically,
the Puerto Ric~n parrot was
abundant, probably numbering in the
millions throughout the island of
Puerto Rico and its satellite islands.
The parrots were found in most of the
major habitat types on the island; from
the moist coastal forest to the montane
rainforest in the northeast, to the moist
limestone and coastal forests of the
northwest, and throughout the forested
central Cordillera. The low montane
habitats originally covered about
35% of the island and it was probably
the major habitat of the parrot.
By the early twentieth century, the
Puerto Rican parrot disappeared from
all satellite islands, and the mainland
population became fragmented. By
1937, only a single isolated population
was left, and they were confined to
the rainforest of the Luquillo Mountains.
1 Surviving Puerto Rican parrots
may still be found only there.
In addition to historical factors that
led to the decline of the Puerto Rican
parrot, problems continued through
the early and mid-1900s.1 The isolated
Luquillo population of Puerto Rican
parrots became even more vulnerable
to storms and hurricanes because all
major weather systems come through
the northeast region of the island. This
population also became vulnerable to
early forest management policies that
led to increased accessibility of
remote areas. It is not uncommon for
Puerto Rican parrots to engage in
vicious, even deadly territorial combats
over the defense of nest sites,
and, during World War II, many trees
of the species preferred by the parrots
for nests (Cyrilla racemiflora) were
selectively cut, not only to provide a
source of energy in the form of charcoal,
but to create jobs. This practice
resulted in a scarcity of optimal nest 

sites. The parrots also contend with
natural enemies such as honeybees
(Apis mellifera) that take over nest
cavities, and minor predators such as
the Puerto Rican boa (Epicrates inoratus)
and rats (Rattus rattus) that are
capable of entering parrot nests and
destroying eggs. The major predator
of the Puerto Rican parrot appears to
be the Red-tailed Hawk (Buteo jamaicensis)
which probably accounts for
the majority of parrot mortality. The
average annual mortality rate is high
among first year parrots, approximately
32%, and declines to approximately
90/o for adult parrots.
Two other significant problems have
been with the Warble Fly (Phi/ornis
pici) that parasitizes parrot nestlings,
sometimes causing death, and with an
ecological competitor, the Pearly-eyed
Thrasher (Margarops fuscatus). The
thrashers are also cavity nesters and
compete with the parrots for nest
sites. Because the thrashers are relatively
recent invaders of Puerto Rico, it
has been speculated that the parrots
have not yet evolved adequate
defense mechanisms against the
thrashers' aggressive and predacious
behavior.
These factors combined, plus the
delayed sexual maturity of the Puerto
Rican parrot to four or five years of
age, have resulted in considerable
reproductive failures: 74% to 88% of
all nests prior to 1973.2 The annual
rate of population decline became
spectacular: it escalated from approximately
8% in the 1950s to over 41% in
the mid-1960s, before dropping to
13% by 1971.1 Population declines
finally leveled off during the 1970s,
but not without severe consequences.
The number of Puerto Rican parrots
decreased by two orders of magnitude:
from an estimated 2,000 in 1937
to approximately 200 in 1953/54 to a
minimum of 13 in 1975.2 The parrot

population has remained relatively
stable over the last decade, and much
of this stability is due to labor intensive
management of the parrot by federal
and commonwealth biologists
and other dedicated personnel and
volunteers.
Conservation of the
Puerto Rican Parrot
Management of the wild population
of Puerto Rican parrots has included
several actions aimed at improving
nesting success. Most of these actions
involved enhancing natural nest cavities,
providing alternative artificial nest
cavities for both Puerto Rican parrots
and Pearly-eyed Thrashers, and maintenance
of nests to prevent water
leaks, and honeybee takeovers.1·2
Also, intense watches (from sun up to
sun down, from approximately February
to June) of all known active nests
are conducted from nearby blinds in
the forest.3 Not only are behavioral
observations made on the parrots
from the blinds, but interventions are
made on behalf of the parrot to safeguard
nests from total failure. In some
cases, wet or unattended eggs are
brought to a nearby aviary for artificial
incubation, or sick or uncared-for nestlings
are brought in for medical attention.
Once hatched or recuperated,
nestlings might be returned to their
original nest. Sometimes nestlings are
exchanged between nests to ensure
that otherwise failing nests would
fledge at least one or more young. As
a result, broods of genetically unrelated
nestlings are sometimes mixed
in a single nest, and genetically related
nestlings fledge from different nests.
After about 14 years (since 1973),
nest success increased from a minimum
of approximately 11% to
approximately 68%,2 but the number
of annual breeding pairs of parrots
and the annual population growth rate
remained low. Only two to five pairs
of Puerto Rican parrots produced an
average of 1.6 young per year. 2 Prior
to Hurricane Hugo in 1988, there were
about 45 to 47 Puerto Rican parrots in
the wild: after Hurricane Hugo there
were approximately 24. Today the
number of Puerto Rican parrots in the
wild is still less than 30.