# Shiny Cowbird

Scientific name: Molothrus bonariensis

Bird group: [icterids](https://birdsofpuertorico.com/family/icterids)

Canonical source: https://birdsofpuertorico.com/bird/278/Shiny-Cowbird

## Identification

The shiny cowbird (Molothrus bonariensis) is a passerine bird in the New World family Icteridae. It breeds in most of South America except for dense forests and areas of high altitude such as mountains. Since 1900 the shiny cowbirds' range has shifted northward, and it was recorded in the Caribbean islands as well as the United States, where it is found breeding in southern Florida. It is a bird associated with open habitats, including disturbed land from agriculture and deforestation.
Physical appearance of the shiny cowbird adult depends on subspecies. Sizes range from 31-40 grams in mass and 18 cm in length (M. b. minimus), to 55-65 grams in mass and 22 cm in length (M. b. cabanisii).


## Distribution and habitat

The Shiny Cowbird is a common resident species native to South 
America but has expanded 
its distribution range north 
throughout the Lesser and Greater 
Antilles, The Bahamas, and the 
Southern United States (Cruz 
and others 1985, Post and Wiley 
1977a, Raffaele and others 1998). The cowbird is believed to have 
arrived in Puerto Rico before 1955 
(Post and Wiley 1977a), where it 
is now established (Bond 1961, 
Raffaele 1989a) and has also 
colonized the island of Culebra 
(Sorrié 1975). In Vieques, the 
cowbird is an uncommon resident 
in spring, summer, and fall, and 
rare in winter (Gemmill 2015). 
This species occurs mostly near 
livestock in open or brushy fields, 
but can also be found in gardens, 
open forests (Oberle 2018), and 
agricultural areas with available 
grains (Raffaele and others 1998), 
as well as into the mountains 
where suitable habitat is available 
(Raffaele 1989b, Raffaele and 
others 1998). The atlas fieldwork 
yielded a total of 502 records 
within 317 hexagons or 66 
percent of the 479 total hexagons 
(see map). Of the 317 hexagons where this species was found, 
breeding met the atlas definition of 
confirmed in 9 percent (27) of the 
hexagons, probable in 32 percent 
(101), and possible in 60 percent 
(189) (see map).

## Breeding

Previously published reports 
indicate that the Shiny Cowbird 
breeds primarily from March 
through July (Raffaele and others 
1998). Cowbirds are brood 
parasites in which the females 
do not build nests, but rather lay 
their eggs in the nests of other 
species, which serve as foster 
parents, incubate the cowbird eggs 
and brood, and feed the nestling 
and fl edgling cowbirds. Cowbird 
nest parasitism has reduced the 
nesting success of several host 
species including the endemic 
Yellow-shouldered Blackbird Shiny Cowbird distribution. The map shows the highest breeding code by hexagon and overlaying the ecological life zones in 
Puerto Rico. Note: percentages may not total 100 due to rounding.       269Shiny Cowbird/Tordo Lustroso(Agelaius xanthomus) (Post and Wiley 1977b) and Puerto Rican 
Vireo (Vireo latimeri) (Woodworth 
1997). The cowbird is a generalist 
in terms of host selection as it has 
been found to parasitize the nests 
of 27 bird species on Puerto Rico, 
although these host species differ 
in their abilities to successfully 
fl edge cowbird young (Wiley 
1985). Cowbird breeding tends 
to coincide with the breeding 
periods of “high-quality” hosts (i.e., 
those that fl edge >55 percent of 
cowbird eggs hatched) and not 
with breeding periods of “low-
quality” hosts (i.e., species that 
fl edge <55 percent of cowbird 
chicks that hatch) (Wiley 1985). 
Atlas results show that this species breeding season extends 
throughout the year with the most 
breeding activity from March to 
June (see chart). The breeding 
activity peaks in May during the 
onset of the rainy season, and the 
overall breeding pattern mostly 
takes place in the subtropical 
moist forest life zone (see chart). 
Results show that this species 
breeds mostly in lowlands within 
the subtropical moist forest life 
zone (58 percent of the hexagons) 
(see table and map). However, 
results indicate that it also breeds 
at higher elevations within the 
subtropical wet forest life zones 
(22 percent of the hexagons), as 
well as in the coastal plains of the 
subtropical dry forest life zones (20 percent of the hexagons) 
(see table and map).

## Conservation

The current population trend for 
the Shiny Cowbird is described 
as increasing. This species is 
currently listed as a species of least 
concern by the IUCN (BirdLife 
International 2016). Locally, this 
species is not listed in any of the 
threatened categories of PRDNER 
and USFWS. In Puerto Rico, the 
Shiny Cowbird has a protected 
habitat in land of about 12 percent 
or 929 km2 of the total area covered by the hexagons where 
evidence of breeding was found 
for this species (7582 km2).

Photo: https://birdsofpuertorico.com/static/images/webp/in_278_Im0.png.webp

Distribution map: https://birdsofpuertorico.com/static/images/webp/in_278_Im1.png.webp

Source note: Text is reproduced from this site's published record. Historical conservation statements and taxonomy have not been independently revalidated. See https://birdsofpuertorico.com/about for source credits and limitations.