for example, on mudflats with active intertidal prey. Even soil invertebrates
move laterally. Movement can sometimes be prevented by prey proof
exclosures. One technique is to compare between the edge and center of
the exclosure to give an indication of extent of movement.- Whether there is compensatory mortality. Excluding the bird species may
increase the local food density, and so attracts another predators undeterred
by the exclosure, such as rodents. This then underestimates the depletion
caused by birds. This can be tested using other exclosures that exclude both
birds and other predators. - Whether the exclosure alters the microclimate and thus affects the survival
and growth of those animals and plants inside. Even netting can have an
impact by reducing wind speed and can also influence sedimentation and
water flow in aquatic environments.
10.5.10Mate provisioning and brood provisioning rates
Such rates are often measured from a hide for set periods of time, varied to reduce
the effect of time of day. Other methods are to use nest cameras with a clock
adjacent to the nest (see 10.2.2) or a camera with a built in clock, perhaps placing
the entire nest on a balance so that from the increase in mass after a feed, the meal
mass can be estimated. This works best for species that consume irregular large
meals at long intervals, such as albatrosses (Huin et al. 2000).
Acknowledgements
Thanks to Aldina Franco, Simon Gillings, Rhys Green, Ian Newton, Ian Sherman,
and Ron Summers for useful suggestions.
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