dead recoveries in 'recaptures only' analyses in migrants

[roodbergen]

Dear people,

I have two questions for you (explanation see below):

1) How should I treat dead recoveries in a 'recaptures only' analysis in a migratory species?
(as a '1', because it did survive the wintering period until found dead at the breeding grounds and was resighted, or as a '0' as it is dead?)

2) Can a joint dead recovery/life recapture analysis be performed if both life and dead recoveries occur in the sampling area, due to increased effort? (so F is not necessarily equal to 1)

I have performed a 'recaptures only' analysis on resighting data of colourbanded Black-tailed godwits (a meadow bird species) at two study sites in The Netherlands.
Godwits migrate to West-Africa in winter. Every breeding season I checked the breeding site (which is also the ringing site, godwits are ringed at their nest) for returning godwits. Godwits that died after returning to the breeding site were given a '1' in the encounter history for the past year (even if they were not seen alive at the breeding site that year, previous to being recovered), as they did survive that year. I wonder if this will not overestimate survival.
I considered performing a joint dead recovery/life recapture analysis, but I am not sure whether my data meet the assumptions. Recoveries/ resightings are both done inside my study areas, as only these areas are searched intensively by the researcher, so F is not necessarily equal to 1. Thank you in advance for your help.

Best regards,

Maja Roodbergen

[cooch]

I have two questions for you (explanation see below):

1) How should I treat dead recoveries in a 'recaptures only' analysis in a migratory species?
(as a '1', because it did survive the wintering period until found dead at the breeding grounds and was resighted, or as a '0' as it is dead?)

No obvious problem using joint models for this - simply have to constrain the fidelity parameter. I suppose you could also treat the 'found dead' as losses on capture, but I suspect there are subtle problems with doing so.

The trick is 'timing' of encounters, dead or alive, relative to the marking period(s). You might need to pursue Barker models as well.

2) Can a joint dead recovery/life recapture analysis be performed if both life and dead recoveries occur in the sampling area, due to increased effort? (so F is not necessarily equal to 1)

Chapter 11, p. 3 - if you only encounter dead individuals in the same sampling area as you mark/live encounter, then F=1 - functionally, if not biologically. The Burnham joint model asumes that dead recoveries can occur anywhere - if this is not the case, then you have to set F=1.