Thanks Andrew, I was wondering about that too, and presumed the numbers would be similar to what you came up with. I also recall a talk I attended a few months ago by Charles Krebs documenting top down food-web control in Canada, where it turned out that the presence of birds of prey controlled the breeding behaviour of their prey due to inducing stress. There are many documented top-down systems where the predators control prey numbers (large rock lobsters in Tasmania is another example, and I vaguely recall something about sea-otters too). There’s also all the stuff about alternate stable states and density dependence where, for example, prey at high densities might be controlled by predators, but at low densities might control predator numbers.
Jeremy O’Wheel
On Wed, Jun 27, 2012 at 9:58 AM, Andrew Taylor
> On Tue, Jun 26, 2012 at 04:02:10PM +1000, Stephen Ambrose wrote: > > Therefore, there is a risk of the WBSE using up too much energy to > > capture a gull in comparison with the energy it would gain from consuming > > one (if it is lucky enough to capture a gull). > > I was curious enough to do back-of-the-envelope calculations from > detailed estimates I found for Bald Eagles. > > Wintering Bald Eagles require about 2000kJ of food/day. > > With smaller size and warmer climate that might be 1500kJ of food/day > for a WBSE. > > A silver gull might weigh 350g, which might equate to 2500kJ. > > So 1 Silver Gull day looks to be enough for a WBSE. > > Bald Eagles are estimated to use ~10kJ/minute in flapping flight and > ~3kJ/minute when soaring/gliding. Active pursuit must burn more energy, > but it looks like an WBSE could easily afford to spend more then an > hour pursuing each gull caught. > > Andrew > =============================== > > To unsubscribe from this mailing list, > send the message: > unsubscribe > (in the body of the message, with no Subject line) > to: birding-aus-request@vicnet.net.au > > http://birding-aus.org > =============================== > ===============================
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