In nature, morphological and behavioral differences among sexes are readily identified, with the exception of cognitive abilities. While the possibility that the sexes differ in their cognition (learning and memory) is much disputed, the best evidence for sex differences comes from tests of spatial ability: males generally do better than females on spatial tasks. Additionally, while males can either use landmarks (visual cues) or spatial cues (distance and direction) to orient themselves, females seem to preferably rely on landmarks. Studying the underlying process behind these differences may help us understand general cognitive mechanisms.
Hummingbirds have proven to be a good model for the study of spatial cognition in the wild, although females have rarely been tested. Taking in to account the differences in foraging strategy between sexes (males are mostly territorial while females are trapliners), Maria Tello Ramos is interested in testing and comparing the ability to learn sequences while foraging.
Above: A male rufous hummingbird visits artificial flowers in a spatial memory task
In some species, males use spatial cues (distance and direction) and feature cues (a colour or a landmark) to relocate a reward while females only use a feature cues. Maria tested whether female hummingbirds of three species use either a spatial cue (location within an array) or a feature cue (colour of the flower) to relocate a rewarded flower. First, the hummingbird had to find the single rewarded flower amongst four flowers of different colours. Upon return the spatial and feature cues were put in conflict. Male rufous hummingbirds first return to the flower at the previous correct location, but what would the females do?
Here, only the yellow flower has nectar in (Phase 1). The hummingbird finds this reward feeds and flies off. On its return the yellow and purple flowers have switched positions (Phase 2). Does it go to the yellow flower (feature cue use) or where the yellow flower was (spatial cue use)?
To test spatial memory, David Pritchard taught hummingbirds to feed from an artificial flower positioned between two landmarks. He then removed the flower and watched to see where each hummingbird searched for it, recording how close the bird stop to where the flower had been positioned using two video cameras 90 degrees apart so the flight path could be recreated and analysed using specialist software.
These experiments will provide some insight into how hummingbirds use landmarks to remember the locations of flowers they have visited.