Age-specificity in territory quality and spatial structure in a wild bird population

Age influences behaviour, survival, and reproduction; hence variation in
population age structure can affect population-level processes. The extent
of spatial age structure may be important in driving spatially-variable
demography, particularly when space-use is linked to reproduction, yet it
is not well understood. We use long-term data from a wild bird population
to quantify covariance between territory quality and age and examine
spatial age structure. We find associations between age and aspects of
territory quality, but little evidence for spatial age structure compared
to the spatial structure of territory quality and reproductive output. We
also report little between-year repeatability of spatial age structure
compared to structure in reproductive output. We suggest that high
breeding site fidelity among individuals that survive between years, yet
frequent territory turnover driven by high mortality and immigration
rates, limits the association between age and territory quality and
weakens overall spatial age structure. Greater spatial structure and
repeatability in reproductive output compared to age suggests that habitat
quality may be more important in driving spatially-variable demography
than age in this system. We suggest that the framework developed here can
be used in other taxa to assess spatial age structure, particularly in
longer-lived species where we predict from our findings there may be
greater structure.