title: Do male and female cowbirds see their world differently? Implications for sex differences in the sensory system of an avian brood parasite.
abstract: BACKGROUND
  Male and female avian brood parasites are subject to different selection pressures: males compete for mates but do not provide parental care or territories and only females locate hosts to lay eggs. This sex difference may affect brain architecture in some avian brood parasites, but relatively little is known about their sensory systems and behaviors used to obtain sensory information. Our goal was to study the visual resolution and visual information gathering behavior (i.e., scanning) of brown-headed cowbirds.
  
  
  RESULTS
  We measured the density of single cone photoreceptors, associated with chromatic vision, and double cone photoreceptors, associated with motion detection and achromatic vision. We also measured head movement rates, as indicators of visual information gathering behavior, when exposed to an object. We found that females had significantly lower density of single and double cones than males around the fovea and in the periphery of the retina. Additionally, females had significantly higher head-movement rates than males.
  
  
  CONCLUSIONS
  Overall, we suggest that female cowbirds have lower chromatic and achromatic visual resolution than males (without sex differences in visual contrast perception). Females might compensate for the lower visual resolution by gazing alternatively with both foveae in quicker succession than males, increasing their head movement rates. However, other physiological factors may have influenced the behavioral differences observed. Our results bring up relevant questions about the sensory basis of sex differences in behavior. One possibility is that female and male cowbirds differentially allocate costly sensory resources, as a recent study found that females actually have greater auditory resolution than males.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana, United States of America. efernan@purdue.edu
authors.forename: Esteban
authors.initials: E
authors.lastname: Fernández-Juricic
authors.forename: Agustin
authors.initials: A
authors.lastname: Ojeda
authors.forename: Marcella
authors.initials: M
authors.lastname: Deisher
authors.forename: Brianna
authors.initials: B
authors.lastname: Burry
authors.forename: Patrice
authors.initials: P
authors.lastname: Baumhardt
authors.forename: Amy
authors.initials: A
authors.lastname: Stark
authors.forename: Amanda G
authors.initials: AG
authors.lastname: Elmore
authors.forename: Amanda L
authors.initials: AL
authors.lastname: Ensminger
mesh_terms: D000818:Animals; D001835:Body Weight; D005123:Eye / Q000033:anatomy & histology; D005260:Female; D019416:Head Movements; D016014:Linear Models; D008297:Male; D009425:Nesting Behavior / Q000502:physiology*; D009929:Organ Size; D010271:Parasites / Q000033:anatomy & histology / Q000502:physiology*; D046109:Passeriformes / Q000033:anatomy & histology / Q000502:physiology*; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology*; D012727:Sex Characteristics
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