Esteban Fernandez-Juricic Lab

at Purdue University





Methodological approaches


Our lab is highly interdisciplinary, as we do research that goes from the cellular level to the community level, with an emphasis on the organism. Therefore, we have several methodological approaches to answer our questions in a comprehensive manner. 
Retinal topography and visual acuity: We study how the density of retinal ganglion cells varies in different parts of the retina (retinal topography) in order to identify retinal specializations that may be used while scanning. We use a retinal wholemount technique to extract and prepare the retinas that are later stained with cresyl violet or DiI. We also estimate visual acuity based on eye size and the density of retinal ganglion cells. 

Bird retina after extraction and flattening

Retinal ganglion cell layer of European starlings

Topographic map of the retina of European starlings

Visual fields. We use an ophthalmic reflex technique to estimate the 3-D distribution of the different portions of the visual fields of birds (binocular, peripheral, blind area, and projection of the pecten). This technique has been used extensively by Prof. Graham Martin (University of Birmingham, United Kingdom). We got trained by Prof. Martin

After a training session with Prof. Martin

The technique consists basically of an eye-exam that we do on a bird with an ophthalmoscope

Three-dimensional visual field of the American crow

Two-dimensional visual field of the American crow

Avian color vision. We have a microspectrophotometer and a focal plane spectrometer, which allow us to establish the peak absorbance of the different visual pigments and oil droplets in the avian retina (including the ultra violet). Additionally, we map the distribution of different types of photoreceptor in the retina by identifying the oil droplets under bright light and fluorescent light. These techniques are essential to better understand the physiological basis of color vision.


Picture of Brown-headed Cowbird oil droplets under bright light

The same area of the Brown-headed Cowbird retina, but under fluorescent light

Temporal visual resolution. We use electroretinography to measure flicker fusion frequency, which is a proxy of the ability of the retina to process visual stimuli at different temporal frequencies

Our gizmo to measure flicker fusion frequencies

Perceptual modeling. We use chromatic and achromatic contrast models to determine the degree to which visual stimuli (predators, prey, mates) stand out from the visual background. We parameterize these models with information on the visual system of our study species that we collect.

Visual contrast models estimate the distance between the object and the background in color space

Centers of visual attention. We are developing an eye-tracker for birds to measure where in the visual field the fovea is projecting.

Output video from our eye tracker

We conduct experiments in semi-natural conditions because they allow us to manipulate factors of interest while controlling for confounding variables and to record the behavior of animals (e.g., scanning, foraging, escape) with multiple cameras (see video examples below).

Experimental set-up to study with multiple cameras responses of birds to an approaching predator (not shown in the picture)

Video center to record bird behavior

Our brand new digital mobile recording station that is battery powered. We can take this anywhere and plug up to eight cameras.

Some examples of our semi-natural experiments on video:

House finches anti-predator behavior in response to a terrestrial predator (stuffed cat on a skateboard)

House sparrow detecting an aerial predator (stuffed hawk)

We use multiple robotic systems to study the behavioral responses of live birds to different types of stimuli (changes in the behavior of members of the same species, predators, etc.). We have developed robot birds using bird skins and micro-servos that can move in different directions (body up and down, head movement, body orientation). We have also used a predator robot that Bird Raptor International manufactures to manipulate predator hunting strategies and study anti-predator behavior. 

This robot cowbird moves its body up and down, along with its head, and after a few minutes...

... it flushes. This generates a stimuli similar to that when birds in a flock flush in response to a predator

Radio-controlled aircraft modified to look and fly like a real hawk. This FALCO robot is manufactured by Bird Raptor International

Some examples of our robots in action on video:

Second generation of robots (body movement in two axes and head movement)

After the robot (triangular cage) directs its visual attention to the other side of the cage, the live bird looks through a window  

We do considerable field work to survey bird populations and study the behavior of individuals in natural conditions (mating displays, vocalizations, anti-predator strategies, foraging, tolerance to disturbance, etc.). We work with common as well as endangered species (e.g., South Western Willow Flycatcher, Belding's Savannah Sparrow).

Simulating recreational activities to study the responses of Black-crowned Night Herons.

Belding's Savannah Sparrows are confined to use remnant salt marshes.

We work most of the time at the beautiful Ross Reserve. This is a picture of the Lindsey Lab. 

In collaboration with Pat Zollner, we are developing individual-based models to study the effects of different types recreational activities on the distribution of animals in natural areas. This virtual tool is very valuable to establish different levels of human visitation to protected areas with the ultimate intention of minimizing the effects of human disturbance.

The lab has all the necessary equipment to extract and stain retinas, and a microscope with a mechanized stage and Stereoinvestigator to estimate density of retinal ganglion cells. The microscope also has fluorescent light to be able to tell apart the different types of oil droplets. We also have a visual field apparatus to measure the configuration of the visual fields and a microspectrophotometer to measure peak absorbance of cones and oil droplets.

We house birds in two rooms we have available in animal facilities. We conduct our behavioral experiments in the lab, in a greenhouse on campus, or at the Ross Reserve (located about 15 min from the Purdue campus). We also do field work in various natural areas in Indiana and neighbor States. The lab has a van to go into the field. 





Last update October 30, 2013