biannual cohorts with annual resighting

[Iain Field]

Dear MARKers,

Please excuse this question if it has been answered before, but simply point me in the right direction.

I have a data set of known age animals that are biannual breeders but have been resighted annually. Animals are marked at birth and followed throughout thier lives. I know how to set up a time and age based matrix for an annual breeder but what about for a biannual one?

The problem I have is that when I import my encounter histories into MARK, the time intervals are correctly set to 1 (1 year) but there are double the number of cohorts as they are born biannually.

I have considered a number of ways to get around this, with the most logical to me, being to make all the null cohorts a dummy parameter in the design matrices? An alternative may be to make the real cohort and the next (null) cohort the same?

Below is a sample of my data:

10101110010000000001000 1 0 ;
10100000010000110001000 0 1 ;
10100000010000010001000 1 0 ;
10100001100000010000000 0 1 ;
10001010100111111100111 0 1 ;
00001101010011111100111 0 1 ;
00101110000000000000000 1 0 ;
00100000000000000000000 0 1 ;
00100000000000000000000 0 1 ;
00100001100000000000000 1 0 ;
00001010100111111100111 0 1 ;
00001101010011111100111 1 0 ;
00001111110111000000000 0 1 ;
00001010001011101000111 0 1 ;

The data is over 23 year and sex code in the group columns.

Any suggestions as to how to set up the design matrix or remove the null cohort would be great.

Many thanks,

iain