DOI: 10.5061/dryad.wstqjq2ht
title: Data from: Shifts in timing and duration of breeding for 73 boreal bird species over four decades

description: Breeding timed to match optimal resource abundance is vital for the
 successful reproduction of species, and breeding is therefore sensitive to
 environmental cues. As the timing of breeding shifts with a changing
 climate, this may not only affect the onset of breeding, but also its
 termination, and thus the length of the breeding period. We use an
 extensive dataset of over 820K nesting records of 73 bird species across
 the boreal region in Finland to probe for changes in the beginning, end,
 and duration of the breeding period over four decades (1975-2017). We
 uncover a general advance of breeding with a strong phylogenetic signal,
 but no systematic variation over space. Additionally, 31% of species
 contracted their breeding period in at least one bioclimatic zone, as the
 end of the breeding period advanced more than the beginning. We did not
 detect a statistical difference in phenological responses of species with
 combinations of different migratory strategy or number of broods.
 Nonetheless, we find systematic differences in species responses, as the
 contraction in the breeding period was found almost exclusively in
 resident and short-distance migrating species, which generally breed early
 in the season. Overall, changes in the timing and duration of reproduction
 may potentially lead to more broods co-occurring in the early breeding
 season – a critical time for species’ reproductive success. Our findings
 highlight the importance of quantifying phenological change across species
 and over the entire season, to reveal shifts in the community-level
 distribution of bird reproduction.
description: 1. Description of methods used for collection/generation of
 data: Raw original data: The Bird Nest Ringing
 Database is coordinated and curated by the Finnish Museum of Natural
 History. This database contains records for ringing
 events of individual bird nestlings (marked by unique Ring IDs) in
 Finland. These data are a subset of the data in the “Database of birds
 ringed in Finland and all reported encounters of the birds” (http://tun.fi/HR.48),
 which is available from the Finnish Biodiversity Information Facility
 (FinBIF) at https://species.fi. The
 primary database was queried by J. Valkama and M. Piha in summer 2018 to
 include only records of ringed nestlings. At the point of data extraction,
 the database contained over 3.6 million ringing records of nestlings for
 166 species (data available from the Finnish Biodiversity Information
 Facility (FinBIF) at https://species.fi), which represents c. 66% of the
 250 bird species known to breed in Finland. Ringing is done by experienced
 volunteer ornithologists who have received training in the procedure
 (Lokki H. (ed.) 2017: Rengastajan käsikirja. Version 1.0. Finnish Museum
 of Natural History, University of Helsinki. (In Finnish). Crucially,
 nestlings can only be ringed when of a certain size (which is
 species-specific), and thus the timing of ringing is tightly linked to the
 timing of egg-hatching (Møller et al. 2010: Climate change affects the
 duration of the reproductive season in birds. Journal of Animal Ecology
 https:/doi.org/10.1111/j.1365-2656.2010.01677.x; Lehikoinen 2011: Advanced
 Autumn Migration of Sparrowhawk Has Increased the Predation Risk of
 Long-Distance Migrants in Finland in PloS One, (2011)
 https:/doi.org/10.1371/journal.pone.0020001.). We therefore use the timing
 of ringing as an indicator for breeding time, since, within species, the
 possible timing of ringing is relatively constant in relation to
 egg-hatching, and has been identified as a functional phenological
 indicator (Møller et al. 2010). Additionally, ringing data has been shown
 to be a reliable estimate for breeding phenology (Eeva et al 2012:
 Breeding time trends of the Crested Tit (Lophophanes cristatus) in
 southern Finland: comparison of data sources. J Ornithol 153,
 653–661). 2. Methods for processing the
 data: To quantify changes in breeding period timing
 and duration of bird species in Finland, we use the Bird Nest Ringing
 Database coordinated and curated by the Finnish Museum of Natural History
 (see 1 above). In order to identify single ringing
 events per nest and day-of-year for each species, we took a number of
 processing steps with the raw data. First, we aggregated individual
 ringing events likely done in the same nest. We used a combination of
 unique <b>R</b>inger ID, <b>S</b>pecies,
 <b>L</b>ocation (unique longitude and latitude) and
 <b>D</b>ate (unique day, month and year) of ringing to
 identify unique ringing events per nest (<b>RSLD</b>
 combinations); this yielded 584 354 events which correspond to a ringing
 event occurring in separate nests by a given ringer on a given day of year
 for each species in the dataset. However, nestlings in several nests may
 have been ringed in the same locations (when nests are located very close
 to each other) and/or more than one ringer may have ringed nestlings
 cooperatively in the same nest, causing the same nest to occur multiple
 times in the database. Therefore, we further divided these records into
 three subsets (A, B and C), based on a brood number (i.e. each ringer’s
 personal chronological sequence of ringed broods) and an abundance value
 (i.e. number of nestlings observed per brood), when available.
 Specifically, a unique brood identifier was created based on the
 combination of <b>B</b>rood and the variables described above
 (<b>RSLD+B=RSLDB</b>). For each RSLDB identifier, we tallied
 the number of ringed nestlings (i.e. number of unique Ring IDs) and
 compared this to the reported abundance value. If these values matched,
 each of these unique broods was considered a unique nest and given a
 unique ID (subset A; 392 421 unique nests). In cases where the tallied
 number of ringed nestlings and the reported abundance value did not match
 (either because the ringer had not ringed all nestlings in the brood, or
 because either the brood number or abundance value was incorrectly
 reported - which of the two was the case we cannot separate) and/or
 abundance values were missing, we used the tallied number of ringed
 nestlings per unique RSLD and disregarded the reported abundance value by
 the ringer, which might or might not be correct. Next, the tallied number
 of nestlings was compared to the maximum brood size for each species
 (literature-based estimates; see traits below). When these values matched,
 the records were assigned a unique nest ID (subset B; 247 399 unique
 nests). For the remaining records, we calculated the potential number of
 nests for each RSLD, by dividing the number of ringed nestlings by the
 maximum brood size for each species. This step was used to calculate the
 required number of nests to “accommodate” the recorded number of nestling
 ringed, which were given a unique ID (subset C; 294 284 unique nests).
 Subsets A, B, and C were then combined, yielding 934 104 records of
 ringing events in unique nests. Finally, we only included records after
 1975, since records before this year were sparse and only represented a
 small subset of the bird species in the dataset. This processing resulted
 in 919 713 records of bird ringing events for 166 species, spanning 43
 years and four bioclimatic zones in Finland (166_species.csv).
 For the purposes of our analyses we further filtered the above
 data set (166_species.csv) through additional criteria. As some species
 had very sparse records, either within a specific bioclimatic zone or over
 time, we included only species-zone-year combinations with a minimum of 30
 records. Next, we included only those species-zone combinations that had
 records from at least 10 years over our study period, and with at least
 one year with observations in the first and one in the last ten years of
 the study period. These relatively conservative inclusion criteria meant
 that many ringing events, and thus several species and species-by-zone
 combinations, were not included in the analysis. These steps were intended
 to ensure that: 1) there were sufficient records to estimate phenological
 metrics for each species in each zone and per year (i.e. enough records to
 represent the day-of-year distribution of nesting events); 2) there was a
 sufficient number of years sampled for each species and zone to reliably
 estimate shifts in the breeding period (i.e. at least 10 data points over
 time); and 3) the species analyzed were present in the beginning and end
 of our study period. We finally excluded one species (<i>Columba
 oenas</i>) as it breeds irregularly and several times throughout the
 season, and thus has an intermittent and varying breeding phenology that
 is not well-captured by ringing data. Finally, we removed apparent
 outliers in the data, i.e. ringing events clearly outside the general
 breeding season of birds in Finland, which most probably represent data
 entry errors (by inspecting the distribution of the nesting events over
 time for each species-zone combination). The final dataset that we used
 for our analyses contained 821 413 records of ringing events in unique
 nests for 73 species (73_species.csv). These data represent a large
 variety of species including birds of prey, waders, passerines, and owls
 that are characterised as Resident ( R) or Short distance migrants (S)
 versus Long distance migrants (L) and single-brooded (1) versus
 multi-brooded (2) species (Traits_73_species.csv).
description: See attached README_RingingDataBorealBirds.txt file