fledgling survival analysis with sparse and incidental data?

questions concerning analysis/theory using program MARK

fledgling survival analysis with sparse and incidental data?

Postby ahannah » Wed Dec 13, 2017 6:39 pm

I am studying a very small population of an endangered songbird, and as part of my research I am studying post-fledging habitat use and (hopefully) post-fledging survival. As such I set out to radio-tag chicks and track them during the post-fledging period.

In 2016 I radio-tagged 4 chicks from 4 nests, and all of the chicks in each nest (tagged and un-tagged) were given unique combinations of colored leg bands so that they could be identified after they left the nest. Due to a poor choice in transmitter attachment method 3 of the transmitters fell off within 48 hours of attachment, and the fourth chick was predated within a day of leaving the nest. In order to determine if the transmitters recovered from the other 3 chicks were due to depredation or early loss I spent a span of 13 days searching for the fledglings that had been tagged with radio-transmitters to be certain if they were alive. I was able to locate 3 of the previously tagged fledglings, and also located one un-tagged sibling during that time. Due to the difficulty in locating fledglings without transmitters and time constraints to collect other data I did not spend more than those 13 days searching for fledglings in 2016. Then in 2017 four of the 2016 chicks returned to breed (two of them had carried transmitters in 2016, and two had not). The two returning 2016 chicks without transmitters were not observed during the short time I looked for fledglings in 2016. The 2016 "season" was in essence only 13 days long.

In 2017, I radio-tagged 6 chicks from 6 nests, and all chicks were given unique combinations of colored leg bands. All transmitters remained attached thanks to a switch in attachment method. One of the radio-tagged chicks was presumed to have been predated after 5 days (too young to move out of study area on own, still dependent on adults, transmitter should not have failed that soon, poorly flighted, poor movement abilities). Radio-tagged chicks were tracked daily, and because the adults split the brood in half and within each half individuals tends to stick relatively close together, I was able to observe an additional 7 chicks (siblings of radio-tagged chicks) occasionally while radio-tracking their siblings. During other portions of my field work I incidentally was also able to observed chicks from two un-tagged/un-banded broods 31 days after they had fledged. I did not search for the halves of broods that did not included radio-tagged fledglings due to the difficulty in locating them. The 2017 "season" was 59 days (from the day the first tagged chick fledged to the day the last tagged chick was observed).

2016
-5 chicks observed over the span of 13 days (4 with tags, 1 without)
- 4 returned in 2017 (two of which were not observed in 2016 after fledging)

2017
-6 chicks were radio-tagged and observed daily over a span of 59 days
-7 siblings were observed occasionally while tracking radio-tagged chicks
-5 unmarked fledglings were observed (with known adults) 31 days after fledging (fledge date known)

I plan on using MARK/RMark to analyze fledgling survival using the nest survival framework. I would like to include all of these data from various sources to be able to increase my sample size. If I only use the 2017 radio-tagged chicks (n=6) then sample size is small and estimated survival is very high due to only one death early in the post-fledging period (not that high survival is bad, but this likely doesn't approximate reality).

2). Is there a good way to estimate survival when 2016 and 2017 "seasons" are so different in length (13 days vs 59 days?

3). Is there a way to incorporate the information from the returning 2016 birds? Since they returned in 2017 I know that they survived the entire year, much longer than the time I spent searching for them during the 2016 breeding season.

Thank you!
ahannah
 
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Re: fledgling survival analysis with sparse and incidental d

Postby ahannah » Fri Jan 26, 2018 2:58 pm

Hi All,

I am still struggling with using the data from 2016 (see above), and am hoping someone can help me out. Writing up my fledgling survival results is stalling because of it.

So bump for awareness I guess.

Any help appreciated!
ahannah
 
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Joined: Tue Dec 12, 2017 4:09 pm

Re: fledgling survival analysis with sparse and incidental d

Postby Bryan Hamilton » Wed Feb 14, 2018 1:37 pm

Hi,

You probably know this but you're data are probably too sparse to do much modeling with.

If you want to get some parameter estimates you'll likely have to collapse everything into as few groups as possible. I would even consider lumping the two years together.

You can (and should) use the incidental observations of the chicks that returned in 2017.

Think about ways to simplify your dataset and recognize that your parameter estimates are going to have lots of uncertainty.
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Location: Great Basin National Park

Re: fledgling survival analysis with sparse and incidental d

Postby JDJC » Wed Feb 14, 2018 3:04 pm

Hi,

Re. 2): Designing the input so that something like a daily survival parameter is being estimated make 2016 and 2017 perfectly easy to reconcile. Observed success over a 13 vs. 59 day period is certainly going to be vastly different, but that's irrelevant--I assume you'd be deriving nest success based upon a shorter survival interval.

Re. 3): Yes, you can incorporate that information by adding more 'alive' observations. You may or may not want to think about how to define the interval length associated with these observations.

John
JDJC
 
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