Population count-based data from surveys provide the information required to estimate changes in populations over time. In order to direct and evaluate management actions, information on population status and change is vital. Population count/index data are also valuable when combined with other data sources in integrated analyses, as this integration allows researchers to not only know the direction of a species’ population trajectory, but the mechanisms that may be responsible for it. For many species, life history characteristics (e.g., low site-fidelity) may make the data used in evaluating population change challenging to collect, thus, trend analysis and integrated models aimed at identifying mechanisms of population change are difficult. Tricolored blackbirds (Agelaius tricolor) are such a species, as they have low site-fidelity and are challenging to count across their range. Given the issues with acquiring accurate count data for species such as tricolored blackbirds, we used relative abundance data from eBird to evaluate the population trend. We used a zero-inflated generalized additive model (ZI-GAM) to estimate the trend of the California tricolored blackbird population from 2007-2016. This model provided estimates of relative abundance to an integrated population model (IPM) framework where the results of the ZI-GAM were analyzed with data from 64,129 tricolored blackbirds banded from 2007-2016 and nesting data from 10 sites from 1992-2016. We used the IPM to estimate adult survival, juvenile survival, fecundity, and population trajectory for tricolored blackbirds.
Results/Conclusions
Mean female annual adult survival ranged from 0.28-0.93 and male survival from 0.17-0.78. Mean juvenile fecundity across all years was 0.21 (CI = 0.0007-0.49), fecundity ranged from 0.46 fledglings per nest in the lowest year to 1.27 in the highest. The trend analysis from the ZI-GAM estimated a population decline of 53% during the study and the IPM estimated a 32% decline (CI = 7.5% growth to 71% decline). The estimated annual population growth rate throughout the study was -0.06 (-0.14 – 0.016). Although the credible interval overlapped zero, 94% of the iterations resulted in a growth rate below zero. Fecundity and female survival are the vital rates most strongly correlated with growth rate, suggesting that these should be the target of conservation action. For species, like tricolored blackbirds, that may be challenging to monitor through more traditional monitoring schemes, data in eBird can be used to estimate large-scale population trends. Data integration and rapidly growing citizen science databases are poised to become powerful tools in conservation science.