Density and atlas reporting rates For the first time for SABAP2 data we attempt to explicitly explore several species’ behavioural and biological attributes that would account for variation in detection and thus reporting rates. While we expected bird density to be the best explanatory variable from the relationship between density and relative abundance modelled above, the relationship with atlas reporting rates was confounded by birds tolerant of human-modified habitats. These had higher reporting rates than expected. To a degree this is not a surprise: most citizen scientist observation efforts will at the very least start in human modified habitats, if not cover them explicitly. The influence of roads on bird distribution is well reported, for instance it has been demonstrated that Orange-breasted Sunbird avoid the road verge (). For this set of Fynbos birds for which densities could be calculated, most were small passerines, and we identified a relationship with reporting rates when correcting when accounting for mass. Given all else is equal, larger birds are more easily detected, but otherwise this relationship was unexpected given the modelling exercise on correlations of relative abundance from the single observer data set. However, the relative abundance index was created from point counts conducted on foot, while most SABAP2 lists are likely compiled to a degree while driving, when larger birds will be more readily detected and hence the importance of mass over the detection covariates. Our density estimates for Fynbos endemic bird species calculated from SABAP2 reporting rates broadly agreed with those published in . While population estimates were consistently lower, the existing published values were based on extrapolation of density estimates to the possible extent of occurrence of these species. This was an area in some cases much larger than the area represented by our current conversion of pentads to area from which population estimates from SABAP2 data were calculated. The pentad area better represents a species area of occupancy for species whose range has been well covered by atlasing efforts. Area of occupancy is typically an area contained within a species extent of occurrence. While this suggests lower SABAP2 population estimates are valid for the Fynbos endemic bird species as they are conservative, upper confidence
Density and atlas reporting rates For the first time for SABAP2 data we attempt to explicitly explore several species’ behavioural and biological attributes that would account for variation in detection and thus reporting rates. While we expected bird density to be the best explanatory variable from the relationship between density and relative abundance modelled above, the relationship with atlas reporting rates was confounded by birds tolerant of human-modified habitats. These had higher reporting rates than expected. To a degree this is not a surprise: most citizen scientist observation efforts will at the very least start in human modified habitats, if not cover them explicitly. The influence of roads on bird distribution is well reported, for instance it has been demonstrated that Orange-breasted Sunbird avoid the road verge (). For this set of Fynbos birds for which densities could be calculated, most were small passerines, and we identified a relationship with reporting rates when correcting when accounting for mass. Given all else is equal, larger birds are more easily detected, but otherwise this relationship was unexpected given the modelling exercise on correlations of relative abundance from the single observer data set. However, the relative abundance index was created from point counts conducted on foot, while most SABAP2 lists are likely compiled to a degree while driving, when larger birds will be more readily detected and hence the importance of mass over the detection covariates. Our density estimates for Fynbos endemic bird species calculated from SABAP2 reporting rates broadly agreed with those published in . While population estimates were consistently lower, the existing published values were based on extrapolation of density estimates to the possible extent of occurrence of these species. This was an area in some cases much larger than the area represented by our current conversion of pentads to area from which population estimates from SABAP2 data were calculated. The pentad area better represents a species area of occupancy for species whose range has been well covered by atlasing efforts. Area of occupancy is typically an area contained within a species extent of occurrence. While this suggests lower SABAP2 population estimates are valid for the Fynbos endemic bird species as they are conservative, upper confidence