Modelling nest age, phase and time

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Modelling nest age, phase and time

Postby jjroper » Mon Dec 01, 2014 11:23 am

Hi all, I will define my terms first.

Nest age - in this case, the number of days since the nest started
Phase - incubation and nestling
Time - the actual time since breeding began

I can imagine a scenario in which nest success appears to be independent of time, but depends on nest age. The simplest situation would be the Skutch hypothesis, in which activity changes at the nest, and so when nestlings are present, predation rates increase. And, if all nests were similar, then, averaged over the breeding season, with nests found at different times, Time could be constant (or appear so).

One way to get at that would be to divide nests into two groups, by phase. For all nests that transitioned (i.e., hatched young) then one would have to consider them successful for the incubation phase and a new nest for the nestling phase. For example:

Nest history
Found day 5
Hatched day 15
Failed day 22, last checked day 21
The history for this nest would be:

FirstFound LastPresent Last Checked Fate NestID
5 21 22 0 1

But, to test the Skutch idea, it should be:

FirstFound LastPresent Last Checked Fate Phase NestID
5 15 15 0 Inc 1
15 21 22 1 Nstlng 1

Those two rows refer to the same nest.This works, but it seems like the hard way to analyse something that might be got at another way.

Also, this implies that daily survival rate is not constant over the nest period itself - but, if all nests were more or less the same, daily survival rate CAN be constant over the nesting season. We can imagine that the daily survival rate (DSR) varies from 0.97 during incubation to 0.95 during nestling phase, for all nests. If nests were initated very asynchronously, and renesting possible, then nests can be initiated at any time during the breeding season and thus, often, incubation and nestling phases are concurrent. Thus, DSR over the breeding season (except perhaps the very first and very last nests) would be constant. Thus, missing the change between the incubation and nestling phases.

Now that I have described my scenario, I hope you all understand the question, which is, can DSR be modeled over the interval of single nests, rather than the breeding season? One way I thought of doing that was arbitrarily making nests synchronous and setting all start days to 1. That, of course, will eliminate the possibility of testing Time (over the breeding season).

Any questions? And answers? Any suggestions?

Thanks,

Jim
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Re: Modelling nest age, phase and time

Postby egc » Mon Dec 01, 2014 1:26 pm

Jim --

This isn't really an RMark-specific question, but is more general, so I'm going to move this thread into the 'Analysis and Design Questions' subforum.
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