Hi,

I am relatively new to R, so please bear with me if this question is too
simplistic/flawed!

I have a radio telemetry dataset with the foraging distances of a number of
birds. Birds are grouped into one of 5 categories depending on their
breeding status, for example females with eggs, females with chicks, paired
males, unpaired males. Here is a sub-set:

Distance travelled (m)    Bird_id       Date          Bird Status
1400                              A         13/5/09       Female with chick
300                                A         14/5/09       Female with
chick
200                                B         13/5/09       Paired male
1400                              B          14/5/09      Paired male
356                                C          13/5/09      Unpaired male

etc etc

I have 30 birds in total and they were tracked for 3 months altogether, with
around 10 distances obtained per bird per night.

My main question is are birds of different breeding status travelling
different distances to forage? As I have repeated observations for each
bird, I decided to do a mixed model with bird id as a random effect. (I
haven't included the issue of date yet as I wanted to try the simplest model
first).

I decided to look at a random intercept model and a random intercept and
slope model, using lme.

I tried the following:

Mlme1<-lme(Sqrt_Distance~Status,random=~1|fBird_ID,data=Distance)
Mlme2<-lme(Sqrt_Distance~Status,random=~1+Status|fBird_ID,data=Distance)
The first model worked, however for the second, I got the error message: nlminb
problem, convergence error code = 1,  message = iteration limit reached
without convergence (10).
I am wondering if this is because I'm trying to test too many things with
too small a dataset?

I then tried the same thing using lme4 this time, and both models worked
with no error messages.

Mlmer1<-lmer(Sqrt_Distance~Status+(1|fBird_ID),data=Distance)
Mlmer2<-lmer(Sqrt_Distance~Status+(Status|fBird_ID),data=Distance)

Is this because lme4 can deal with this kind of data better or is there
still a flaw in the model process?
I would like to see if date is having an effect on the distance travelled
too, but at the moment, I'd just like to see if I am going about this the
correct way.

Thank you in advance for any help,
Katrina

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