Hooded Warbler Habitat Selection
By Gregory Gough
Male and female hooded warblers separate into different habitats in the non-breeding season. In the Yucatan Peninsula in Mexico long-running studies revealed that males occupy forest habitat while females are in the treefall gaps, forest edges, and other adjacent shrubby habitats.
The key difference between the male and female habitats is the orientation of the vegetation. Males like their plant stems to be up and down while the females prefer their stems to be at an angle.
So ingrained is this preference that laboratory studies of hand-raised hooded warblers revealed that strips of black crepe paper arranged vertically were preferred by males whereas oblique arrangements were preferred by females.
But what would happen if the vegetation structure changed? In 1988, Hurricane Gilbert slammed into the study area and snapped off many a tree top.
In areas that had previously been the provenance of males, and had suffered significant changes to the vertical structure of the forest, females moved in. In areas that were relatively untouched the males remained.
This article summarizes the information in this publication:
Morton, Eugene S., Van der Voort, M. and Greenberg, Russell S. 1993. How a warbler chooses its habitat: Field support for laboratory experiments. Animal Behaviour, 46: 47-53
During the non-breeding season hooded warblers, Wilsonia citrina, defend individual territories and segregate by sex into different habitats. Previous laboratory trials suggested that choice was based upon the verticality of plant features: males prefer habitat with more stems growing vertically, whereas females prefer vegetation predominated by oblique angles. To test the proximate cues used by hooded warblers to assess habitat suitability, the effect of hurricane disturbance on the distribution of the sexes was investigated. Hurricane Gilbert crossed the northern portion of the Yucatan Peninsula, Mexico in mid-September 1988 with 320 km/h winds. The abundance and distribution of each sex was compared before and after the storm. After the storm females appeared in forests previously occupied only by males. Analysis of the angles, size, and density of vegetative stems showed that females were found on territories where the verticality of the vegetation was reduced compared with the verticality of vegetation in territories still defended by males. Vegetative height did not differ in male and female territories. This result supports laboratory predictions that primary cues for habitat segregation are based on the relative amounts of vertical and oblique elements in the habitat.
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