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A. Cruz

Publications and source records attributed to A. Cruz.

6 recordsLinked to original sources
USGS2017

The decline of an adaptation in the absence of a presumed selection pressure

The colonial nesting Village Weaver ( Ploceus cucullatus ) lays eggs that vary in ground color and pattern, but individual females lay similar eggs each time. Tests on captive African stocks have shown that females reject eggs of other cohorts if such eggs are sufficiently different. The Village Weaver may have evolved rejection behavior and variable eggs in response to cuckoo parasitism in Africa. The Village Weaver was introduced into Hispaniola from Africa as early as the 18th century. Before the arrival of the Shiny Cowbird ( Molothrus bonariensis ) in the early 1970's, there were no brood parasites on Hispaniola. Furthermore, in an experimental parasitism study, Hispaniolan Village Weavers accepted both dummy eggs and dissimilar Village Weaver eggs. The Village Weaver may have decreased the egg‐rejection behavior in the absence of the selective pressure of brood parasitism. Now Hispaniolan populations of the Village Weaver are parasitized by the Shiny Cowbird, which lays eggs dissimilar to those of the weaver. Brood parasitism by the Shiny Cowbird exerts a detrimental impact on the Village Weaver by reducing nest success and productivity.

Evolution↗
USGS2008

Egg rejection behavior in a population exposed to parasitism: Village Weavers on Hispaniola

In contrast to African Village Weavers (Ploceus cucullatus) that are parasitized by Diederik Cuckoos (Chrysococcyx caprius), introduced weavers on Hispaniola existed without parasitism for at least 2 centuries until the arrival of the Shiny Cowbird (Molothrus bonariensis) in the 1970s. Cruz and Wiley (1989) found that Hispaniolan weavers had a lower rejection rate of foreign eggs than African populations. Subsequently, Robert and Sorci (1999) and Lahti (2005, 2006) found that acceptance of dissimilar eggs is not characteristic of the species throughout its Hispaniolan range. In 1999-2002, we studied egg rejection in Hispaniolan weavers on a broad regional scale. Rejection increased as experimental eggs became increasingly different from the host eggs. Rejection rates for mimetic eggs, different color eggs, different-spotting eggs, and cowbird eggs was 23.2%, 33.3%, 61.5%, and 85.3%, respectively, with higher rejection of cowbird eggs in areas where cowbirds were observed. Although rejection is likely to have a genetic component, the differences could be due to phenotypic plasticity. Plasticity in egg rejection may be expected, given the potential cost of rejection and the spatiotemporal distribution of cowbirds. Thus, egg rejection has not necessarily decreased in Hispaniolan weavers, but it may act in a plastic manner, increasing where cowbirds are present. ?? The Author 2008. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.

Behavioral Ecology↗
USGS2007

Effects of experimental egg composition on rejection by Village Weavers (Ploceus cucullatus)

We experimentally parasitized nests of the Village Weaver (Ploceus cucullatus) in Hispaniola using real and artificial eggs made from wood and modeling clay. Artificial eggs were similar in size and shape to real weaver eggs and were coated with acrylic paint and glazed. Real eggs were actual weaver eggs taken from Village Weaver nests. Experimental parasitic eggs (1) mimicked natural weaver eggs, (2) differed in color only, (3) differed in spotting only, or (4) mimicked Shiny Cowbird (Molothrus bonariensis) egg color and spotting pattern. Parasitized nests were checked after 2-6 days. Real eggs were ejected from weaver nests with increasing frequency as they became less similar to the eggs in the nest with cowbirds eggs having the highest rejection (81%). However, for artificial egg types there were no significant within-composition differences in patterns of rejection. Clay eggs were usually ejected from the nests, whereas nests containing wood eggs often ended empty, or with only the artificial egg remaining in the nest. These patterns may reflect the differential ability of weavers to recognize and remove foreign eggs of different compositions from their nests. Researchers undertaking egg-rejection experiments should use real eggs either in addition or in place of artificial eggs to assess the cost of rejection and the coevolutionary relationships between parasite and host.

Wilson Journal of Ornithology↗
USGS1991

Conservation of the yellow-shouldered blackbird Agelaius xanthomus, an endagered West Indian species

The yellow-shouldered blackbird Agelaius xanthomus , endemic to Puerto Rico and Mona Island, is endangered, mainly because of brood parasitism by the shiny cowbird Molothrus bonariensis , which reached Puerto Rico at least 30 years ago. The yellow-shouldered blackbird populations have since declined, about 770–1200 remaining (470–900 on Mona Island) by 1982–1986 compared to a population of about 2400 in 1975. Nearly all nests of blackbirds in most of its habitats are parasitized by cowbirds. This significantly reduces nesting success, but blackbirds have evolved no defenses against brood parasitism. Removal of cowbirds from the yellow-shouldered blackbird nesting grounds, modeled after similar programmes for the brown-headed cowbird Molothrus ater on Kirtland's warbler Dendroica kirtlandii nesting areas, significantly increased blackbird production. Blackbirds readily accept nest boxes, and breeding populations can be established in otherwise unusable sites and can be concentrated in mangrove habitats, were they are more easily protected by cowbird removal. Furthermore, yellow-shouldered blackbird pairs using cavities, including nest boxes, fledged more young per nest than pairs using open nests.

Boquerón Commonwealth Forest, Roosevelt Roads Nava↗
USGS1989

The shiny cowbird Molothrus bonariensis in the West Indian region--Biogeographical and ecological implications

The shiny cowbird (Molthrus bonariensis), an avian brood parasite, is endemic to South America, Trinidad, and Tobago, but during the last 100 years the species has spread through the West Indies. Successful colonization by the shiny cowbird depends on the availablitiy of suitable habitats and host species. As forest fragmentation increases in the West Indies, new hosts, particularly forest species, will be parasitied. Forest fragmentation creates small patches of forests surrounded by open habitat and increases the portion of forest habitat available to cowbirds.

Book chapter↗