A ‘cold’ (unincubated) egg
In 2010, egg neglect was recorded in 38% of nests, from regular visual inspections of nests to see if an adult bird was present or not. Eggs that endured chilling of up to 12% of the total incubation period still managed to hatch successfully and 70% of those chicks successfully fledged. Neglect resulted in the lengthening of the incubation period by up to about 5 days. It would be desirable to develop a means of monitoring egg neglect that didn’t involve the high labour of checking nests regularly throughout a long incubation period (at least 39 days) and does not involve the intrusion of shining a torch in nests every day. It is hoped that this can be achieved remotely with the use of temperature loggers. I-buttons are the size of a large watch battery and record temperature (as frequently as you like) and store the readings in an internal memory. The i-buttons have to then be retrieved to download the readings.
An i-button which records temperature at intervals of your choice up to a maximum of 1048 readings
It may be relatively straight-forward deploying i-buttons in the nests of ground-nesting birds, which are readily accessible and have an obvious nest-cup (where the egg(s) are laid), but it is rather more of a challenge when it comes to Storm Petrels. The cavities and crevices that they nest in are, more often than not, out of sight, let alone within reach. Those that are accessible generally involve squeezing and manipulating your hand and arm through the maze of cavities within the dry-stone walls (or ‘dykes’ as they’re known in Shetland) and relying on your sense of touch, rather than sight. The many bruises and scrapes we have endured are evidence of this. In addition, it is often not obvious where a pair is likely to lay their egg. Storm Petrels don’t build much of a nest; at the very most, there may be a slight depression, which may be lined with a bit of dead grass. A logger can only be deployed if the substrate is soft mud, within which it can be sunk into, such that it is level with the surface; if it were to protrude from the surface, a fragile egg could be knocked against it and broken.
Struggling to access a nest-cavity and deploy a temperature logger within the nest-cup
If a bird is incubating an egg over a temperature logger, it is anticipated that the temperature logger will record a higher temperature than ambient temperature. However, Storm Petrels incubate their eggs at a fairly low temperature – a lot lower than most other birds – which is probably an adaptation to enable them to endure such long incubation shifts without feeding and explains the slow development of embryos. Consequently, to confirm the presence or absence of a bird, a second temperature logger is deployed within the nest, but outside of the nest-depression. When temperature loggers are retrieved, once a chick is hatched (or an egg has been abandoned), we will be looking for a difference in temperature between the two loggers.
It is hoped that this remote means of monitoring egg neglect will provide an absolute measure of neglect for the entire period of incubation, without the need for somebody to check nests every day and without causing any disturbance to breeding birds. Fingers crossed it works!