Nocturnal giant dinosaurs and complex archosaur social behavior

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com

A couple of recent papers that may be of interest regarding the
behavior of dinosaurs and large Mesozoic archosaurs:

Nocturnal dinosaurs to avoid heat stress?

M. F. Rowe, G. S. Bakken, J. J. Ratliff and V. A. Langman (2013)
Heat storage in Asian elephants during submaximal exercise: behavioral
regulation of thermoregulatory constraints on activity in endothermic
gigantotherms.
Journal of Experimental Biology 216: 1774-1785
doi: 10.1242/jeb.076521
http://jeb.biologists.org/content/216/10/1774.abstract


Gigantic size presents both opportunities and challenges in
thermoregulation. Allometric scaling relationships suggest that
gigantic animals have difficulty dissipating metabolic heat. Large
body size permits the maintenance of fairly constant core body
temperatures in ectothermic animals by means of gigantothermy.
Conversely, gigantothermy combined with endothermic metabolic rate and
activity likely results in heat production rates that exceed heat loss
rates. In tropical environments, it has been suggested that a
substantial rate of heat storage might result in a potentially lethal
rise in core body temperature in both elephants and endothermic
dinosaurs. However, the behavioral choice of nocturnal activity might
reduce heat storage. We sought to test the hypothesis that there is a
functionally significant relationship between heat storage and
locomotion in Asian elephants (Elephas maximus), and model the
thermoregulatory constraints on activity in elephants and a similarly
sized migratory dinosaur, Edmontosaurus. Pre- and post-exercise (N=37
trials) measurements of core body temperature and skin temperature,
using thermography were made in two adult female Asian elephants at
the Audubon Zoo in New Orleans, LA, USA. Over ambient air temperatures
ranging from 8 to 34.5°C, when elephants exercised in full sun, ~56 to
100% of active metabolic heat production was stored in core body
tissues. We estimate that during nocturnal activity, in the absence of
solar radiation, between 5 and 64% of metabolic heat production would
be stored in core tissues. Potentially lethal rates of heat storage in
active elephants and Edmontosaurus could be behaviorally regulated by
nocturnal activity.

Also blog:
http://jeb.biologists.org/content/216/10/iii

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Complex social and breeding behavior in crocodiles:


Campbell, H.A., Dwyer, R.G., Irwin, T.R.& Franklin, C.E. (2013)
Home Range Utilisation and Long-Range Movement of Estuarine Crocodiles
during the Breeding and Nesting Season.
PLoS ONE 8(5): e62127.
doi:10.1371/journal.pone.0062127
http://phys.org/news/2013-05-boss-crocs-rethinking-crocodile.html

The estuarine crocodile (Crocodylus porosus) is the apex-predator in
waterways and coastlines throughout south-east Asia and Australasia.
C. porosus pose a potential risk to humans, and management strategies
are implemented to control their movement and distribution. Here we
used GPS-based telemetry to accurately record geographical location of
adult C. porosus during the breeding and nesting season. The purpose
of the study was to assess how C. porosus movement and distribution
may be influenced by localised social conditions. During breeding, the
females (2.92±0.013 metres total length (TL), mean ± S.E., n = 4)
occupied an area<1 km length of river, but to nest they travelled up
to 54 km away from the breeding area. All tagged male C. porosus
sustained high rates of movement (6.49±0.9 km d-1; n = 8) during the
breeding and nesting period. The orientation of the daily movements
differed between individuals revealing two discontinuous behavioural
strategies. Five tagged male C. porosus (4.17±0.14 m TL) exhibited a
'site-fidelic' strategy and moved within well-defined zones around the
female home range areas. In contrast, three males (3.81±0.08 m TL)
exhibited 'nomadic' behaviour where they travelled continually
throughout hundreds of kilometres of waterway. We argue that the
'site-fidelic' males patrolled territories around the female home
ranges to maximise reproductive success, whilst the 'nomadic' males
were subordinate animals that were forced to range over a far greater
area in search of unguarded females. We conclude that C. porosus are
highly mobile animals existing within a complex social system, and
mate/con-specific interactions are likely to have a profound effect
upon population density and distribution, and an individual's travel
potential. We recommend that impacts on socio-spatial behaviour are
considered prior to the implementation of management interventions.