Research
Insect adhesion and locomotion
As a postdoctoral research associate in Walter Federle's lab at the University of Cambridge, I investigated the role of compliance and subsurface structures in insect adhesion and how these scale with size.
Investigating the diversity of gecko locomotion
As a postdoc in Tim Higham's lab at the University of California, Riverside, my main focus was to understand the diversity of gecko locomotion with a focus on the large variation in the gecko's adhesive toe pads. The gecko adhesive system is highly varied, but we know little about how the different adhesive morphologies relate to habitat, evolutionary lineage or locomotor patterns. The Pachydactylus radiation of geckos is a large and diverse group found in southern Africa. We visited Namibia to be able to work in the field and collect specimens for both morphological and biomechanical research. This work involved methods of morphological measurements and 3-D kinematics using high speed video.
Scaling of running stability and limb posture with body size in galliform birds
For my PhD thesis, supervised by Monica Daley and John Hutchinson (at the Structure and Motion Lab, Royal Veterinary College, UK), I investigated how locomotor strategy changed in uneven terrain with birds of differing body mass. I used the galliforms; a bird group including quail, pheasants, fowl and turkeys, and ostriches as my study species.
These birds not only incorporate a 500-fold body mass change but also exhibit large changes in leg posture. Small birds, such as the quail, have very crouched postures - their legs have a very 'z-like' shape. In contrast, the larger massed species such as the ostrich have a more upright posture, similar to humans.
I studied whether these changes in body mass and leg morphology displayed discreet strategies whilst moving over obstacles in a runway. I used Kistler force plates and Qualisys Motion Capture cameras to obtain both kinetic and kinematic data. I also changed the height of the obstacle to observe if strategies changed with the difficulty of the terrain.
In a single species, pheasants, the birds did not change their obstacle negotiation strategy with increasing obstacle height. The birds also anticipated the upcoming obstacle, which allowed them to control how they landed on and after the obstacle reducing the leg loading they experienced (Birn-Jeffery & Daley 2012). This reduction in leg loading helps prevent injury or complete failure of the limb. When looking at the whole range of bird body masses, conversely to expectations, all the birds adopted the same strategy as the pheasants when going over all the obstacle heights (Birn-Jeffery et al., 2014). These findings suggest a universal control policy over uneven terrain across a large body mass range.
Analysis of extant bird and lizard claws to infer mode of life in non-avian theropods
I carried out my MSci project at Bristol University and was supervised by Emily Rayfield. I took measurements on claw curvature and thickness from extant bird and squamate claws whilst taking note of their behaviour (ground-dwelling, perchers etc...). I then used this dataset to try and determine if the differing behavioural categories could be separated by their claw morphology alone. I accounted for phylogeny and then plotted non-avian theropod claws into this morphospace to observe if mode of life could be determined.
There was little correlation between claw morphology and behaviour; although ground-dweller animals possess less curved and relatively thick claws compared to other behavioural categories (Birn-Jeffery et al., 2012). These findings suggest other morphological features should be used in any future work to determine the mode of life in extinct theropods.
I then furthered this study by creating 2-D finite element models of example specimens from each extant behavioural category using COSMOSM Geostar. Mechanical properties were given to each model and were loaded using the estimated static ground reaction force in a 'standardised loading', for direct comparison between all samples, and a 'perch/climbing' load. Non-avian theropod claws were also modelled and loaded using the same technique. Behaviour was separable by the stresses and strains the 2-D claws underwent; with perching and climbing claws showing arboreal specialisations. Predatory and ground-dweller claws were highly varied and experienced the greatest stresses.
