Movements and Orientation

1
Movements and Orientation
Why move?
Acquisition of Resources - food and water
- mates - basking or hibernation sites
- nesting sites - etc.
Costs and Benefits
- Energy - Predation - Exposure
2
Movements and Orientation
Why move?
Herps - most are small - a few travel
long distances
Consider - home ranges - territories -
migration - dispersal - homing
3
Movements and Orientation
Movement and Biology
Individuals - water and temperature -
foraging strategy - energy balance - mating
system - predation pressure - interspecific
encounters
Populations - metapopulations - genetic
structure - philopatry - conservation
corridors
e.g., dispersal often high juvenile mortality
toads sea turtles clutch size
4
Movements and Orientation
Methods
Mark and Recapture...
Continuous Monitoring...
5
Movements and Orientation
Types of Movement
1. Station keeping (home range) - foraging -
commuting - defense
2. Ranging Dispersal - mate searching
3. Dispersal - increase space between indivs
4. Migration
6
Movements and Orientation
Home Range Movements
(Convex polygon, Other methods)
Effect of body size and ecology
- Fidelity - Shifting - Nomadic
Pough et al. 2001
7
10-4, Pough et al. 2001
Movements and Orientation
Resources
1. Depleted or 2. Not depleted
Varanus komodoensis
-Green and Marine Iguanas
Small home ranges if abundant resources or
quickly regenerated
Large home ranges (or nomadic) if patchy
resources or slowly regenerated
- Dermochelys - Vertebrate Diet
Predict from abundance, patchiness, renewal rate
of food
8
Movements and Orientation
Territoriality ( Home Range Defense)
Predict from abundance, patchiness, renewal rate
of food
Costs of Defense vs. Increased availability
of resources
Favored if - resources moderately abundant -
even or moderately patchiness - high renewal
rate
Not Favored if - very high or very low resource
abundance - high patchiness - low renewal rate
9
Movements and Orientation
Territoriality
- Patchy distribution favors overlap of home
ranges
- Only use a small portion of HR at one time
- Too costly to defend (e.g., small verts or
hidden insects)
HR defense - rare in actively foraging lizards
- common in sit-n-wait insectivores
Pough et al. 2001
10
Movements and Orientation
Territoriality
Sexual differences ( lizards)
Female - not territorial - home ranges
overlap - may defend nest sites
(smaller than HR)
Male - often territorial - includes HRs of
several females - related to mating more than
food
Satellite Males
11
Movements and Orientation
Spools PIT tags Genetics Radios Fluorescent
Powder etc.
Territoriality
Sexual differences ( lizards)
Female - not territorial - home ranges
overlap - may defend nest sites
(smaller than HR)
Male - often territorial - includes HRs of
several females - related to mating more than
food
Satellite Males
12
Movements and Orientation
Territoriality
Density
12
6
6
Pough et al. 2001
13
Movements and Orientation
Territoriality
Site Defense
Non-depletable resources - burrows - basking
sites
Some actively foraging lizards without HR defense
Plethodontid salamanders moist retreats under
logs, rocks
14
Movements and Orientation
Migrations
about Resources
Annual/cyclical basis - breeding areas -
nesting sites - hibernation dens - feeding
areas
Changing habitat - droughts/floods - e.g.
drying ponds
15
Movements and Orientation
Migrations for Amphibian Mating
- To aquatic breeding sites - Weather dependent
Rana in Europe up to 15 km most only a few
hundred meters
- Breeding site fidelity common e.g., newts in
California for 11 years
16
Movements and Orientation
Migrations for Reptile Mating
- not that common - females moving to suitable
nesting sites - sometimes aggressive defense
Most squamates nest in HR
Green iguanas in Panama swim to small sandy
island to nest
17
Movements and Orientation
Migrations for Reptile Mating
Sea Turtles
Chelonia mydas
Thousands of kilometers Feeding areas to nesting
beaches
Dermochelys travels farthest
Site Fidelity - Feed together - Nest at
original beach - Males similar?
10-8, Pough et al. 2001
18
Movements and Orientation
Overwintering Migrations
- e.g. Rana clamitans summer in pond winter
in stream
- e.g. Crotalus viridis overwinter communally
19
Movements and Orientation
Juvenile Movements
- Suitable Habitat - Adult Competition
e.g. - amphibs from water to land -
turtles from land to water
e.g. - unoccupied habitat (Bufo marinus) -
avoid cannibalism
Rare long distance dispersal Heterozygosity
20
Movements and Orientation
Juvenile Reptile Movements
- Most squamate offspring in parents HR
To Disperse or NOT disperse
-scarce resources -mating with relatives
-cannibalism -long-lived species
-exposure to predation -energetically costly
-move to marginal habitat -high adult mortality
- Dispersal (and sociality) from nesting
aggregations
- Iguana iguana in Panama - crocodilians - sea
turtles
21
Movements and Orientation
Homing Behavior
Ability to return to home range or breeding site
Species differ in homing ability
Mmmm doughnuts
Amphibs - Plethodontids up to 60m -
Taricha newt 2-8 km
Ability correlated with HR size?
Reptiles - turtles, crocodiles often move
many km - lizards, snakes not well-studied
ability to return correlated w/ territoriality
Motivation
22
Movements and Orientation
Orientation
1. Local 2. Compass 3. Magnetic/Navigation
1. Local - Visual and chemical cues
Plethodontids?
Sceloporus?
- Audio cues e.g. breeding pond
- use multiple cues
start
10-13, Pough et al. 2001
23
Movements and Orientation
Orientation
1. Local 2. Compass 3. Magnetic/Navigation
1. Local
Some local cues reliable even in new environment
- Downhill orientation (newts toward water)
- Orientation toward bright blue and purple light
(hatchling sea turtles moving toward ocean)
24
Movements and Orientation
Orientation
1. Local 2. Compass 3. Magnetic/Navigation
2. Compass
Ability to orient w/o local cues
- Y-axis orientation
- Sun Moon, star
10-16, Pough et al. 2001
25
Movements and Orientation
Orientation
1. Local 2. Compass 3. Magnetic/Navigation
2. Compass
Ability to orient w/o local cues
- Y-axis orientation
- Sun Moon, star
10-16, Pough et al. 2001
26
Movements and Orientation
Orientation
1. Local 2. Compass 3. Magnetic/Navigation
2. Compass
- Sun pineal organ (third eye) in all but
crocs
10-18, Pough et al. 2001
Important for - photoperiod entrainment -
circadian rhythms - internal clock
In some lizards more advanced parietal eye
(with retina, lens, cornea)
27
Movements and Orientation
Orientation
1. Local 2. Compass 3. Magnetic/Navigation
2. Compass
- Sun polarized light
- atmosphere scatters light - e-vector
perpendicular to suns rays - related to
position of sun - overcast interferes
10-20, Pough et al. 2001
Detect with extraoptic photoreceptors
(usually pineal body)
28
Movements and Orientation
Orientation
1. Local 2. Compass 3. Magnetic/Navigation
3. Magnetic Orientation and Navigation
True Navigation 1. Compass Sense 2. Map
Sense
some herps can - detect earths magnetic field
- relate to gravitational field (sea turtles) -
magnetic receptors not well understood
- amphibs, alligators, box turtles, sea turtles
- probably use with chemical and visual cues
29
Navigation via Magnetic Fields

• Pelagic Whales
• Homing Pigeons
• Cave salamanders
• Bacteria etc.

- often a redundant system
- Magnetite particles (Fe3O4) orient with
magnetic field
- Receptors detect -gt processed in CNS