Anthropogenically-Mediated Density Dependence in a Declining Farmland Bird
Fig 1
Nestling provisioning rate was influenced by an interaction between NND and corvid abundance.
Points show raw data with corvid abundance split into above and below median values (corvid abundance is categorized in the graph for ease of visualization but designated as a continuous variable in the model). Lines are predicted from the final averaged model (Table 7) with median values of other factors causing additional variation in the final model (nestling age = 5 days, brood size = 3 nestlings, temperature = 15°C, year = 2008, farm management = conventional), at the two extremes of observed corvid activity levels along with the median value (low = 0; high = 59; median = 3 corvids passing within 100m of the nest in a 20 minute period prior to assessment of yellowhammer provisioning rate). 95% confidence intervals are shown for all three predictions. For 5 points where provisioning rate was constant for the same nest on more than one occasion, we have added a slight ‘jitter’ (± 0.1 provisioning trip) for display purposes only to allow sample sizes to be visualized.