DOI: 10.5061/dryad.8vc80
title: Data from: Understanding the contribution of habitats and regional variation to long-term population trends in tricolored blackbirds

description: Population trends represent a minimum amount of information required to
 assess the conservation status of a species. However, understanding and
 detecting trends can be complicated by variation among habitats and
 regions, and by dispersal connecting habitats through source-sink
 dynamics. We analyzed trends in breeding populations between habitats and
 regions to better understand the overall dynamics of a species'
 decline. Specifically, we analyzed historical trends in breeding
 populations of tricolored blackbirds (Agelaius tricolor) using breeding
 records from 1907 to 2009. The species breeds itinerantly and ephemerally
 uses multiple habitat types and breeding areas, which make interpretation
 of trends complex. We found overall abundance declines of 63% between 1935
 and 1975. Since 1980 overall declines became nonsignificant and obscure
 despite large amounts of data from 1980 to 2009. Temporal trends differed
 between breeding habitat types and were associated with regional
 differences in population declines. A new habitat, triticale crops (a
 wheat-rye hybrid grain) produced colonies 40× larger, on average, than
 other breeding habitats, and contributed to a change in regional
 distribution since it primarily occurred in a single region. The mechanism
 for such an effect is not clear, but could represent the local
 availability of foodstuffs in the landscape rather than something specific
 to triticale crops. While variation in trends among habitats clearly
 occurred, they could not easily be ascribed to source-sink dynamics,
 ecological traps, habitat selection or other detailed ecological
 mechanisms. Nonetheless, such exchanges provide valuable information to
 guide management of dynamic systems.
description: Graves_et_al_data1 (full
 data except geographical regions)Data sources are
 described in the published paper. Data file contains headers and 1964
 other rows (total of 1965 rows). Missing values are indicated by NULL.
 Variable names: descriptions. County: text of county name.
 observation_date: month/day/year for original observation. location_name:
 text name given to the location in the Tricolored Blackbird Portal
 (http://tricolor.ice.ucdavis.edu). observer: text for observer’s name.
 bird_count: integer for the total number of birds reported.
 primary_substrate: text name the breeding substrate listed in the record
 as either the dominant kind of vegetation or the first listed kind. NULL
 indicates no data were available. secondary_substrate: text name for a
 second or less common breeding substrate listed in the record. NULL
 indicates no data were available, which is the case for the majority of
 records because only a single substrate was recorded in the record.
 Colony: yes or no for whether the record comes from a breeding colony or
 not. NULL indicates it was not clear and the data were therefore omitted
 from breeding colony analyses.Graves_et_al_data1.csvGraves_et_al_data2 (has geographical regions but no observer names or secondary substrates)Data file contains headers and 1964 other rows (total of 1965 rows). Missing values are indicated by NULL. Variable names: descriptions. Region: Text name for geographical regions of the state corresponding to Figure 2(c) in Graves et al. (2013). observation_date: month/day/year for original observation. location_name: text name given to the location in the Tricolored Blackbird Portal (http://tricolor.ice.ucdavis.edu). bird_count: integer for the total number of birds reported. primary_substrate: text name the breeding substrate listed in the record as either the dominant kind of vegetation or the first listed kind. NULL indicates no data were available. Colony: yes or no for whether the record comes from a breeding colony or not. NULL indicates it was not clear and the data were therefore omitted from breeding colony analyses.Graves_et_al_data2.csv