Giant Cowbird eggs in the nests of two icterid hosts: the use of morphology and electrophoretic variants to identify individuals and species

Article Abstract:

A field study was conducted near Panama City, Republic of Panama, to determine whether the eggs of the Giant Cowbird (Schaphidura oryzivora) could be distinguished from the eggs of its hosts on the basis of physical appearance or chemical content. The study also tried to ascertain whether more than one female cowbird parasitized one nest. Egg morphometric analysis and protein electrophoresis were used to distinguish the eggs of the host species from those of the cowbirds. Differences between the eggs of the hosts and the cowbirds were ascertained, while evidence of multi-parasitism was not conclusive.

Bird populations, Panama

Removal of yellow warbler eggs in association with cowbird parasitism

Article Abstract:

The host-egg stealing of Brown-headed Cowbird (Molothrus ater) from parasitized Yellow Warbler (Dendroica petechia) is an instinctive part of the former's brood parasitism. Female cowbirds remove one egg on a day before or after they have laid their own eggs. The stolen eggs are often eaten. Host-egg removal does not deceive hosts into accepting parasitic eggs, and nest abandonment by the host is not the result of parasitic or predatory disturbance. Cowbirds steal host-eggs for enhanced incubation efficiency in parasitized nests. Yellow warblers incubate all the eggs in its nest.

Research, Bird eggs, Bird nests

Effects of nest parasitism by the brown-headed cowbird on nesting success of the California gnatcatcher

Article Abstract:

The brown-headed cowbird of North America is a nest parasite that has been implicated in the decline of many passerines, including threatened and endangered species such as the California Gnatcatcher, of which there are only some 2,000 pairs in the US. A new study examines the effect of nest parasitism by the brown-headed cowbird on the nest-fate of California gnatcatcher eggs. The study shows that nest abandonment and predation is more important to nest success than parasitism, which may have a secondary role.

Patient outcomes, Mortality, Observations, Eggs, Eggs (Biology), Incubation, Gnatcatchers