Research ArticleAVIAN ECOLOGY

Resource tracking within and across continents in long-distance bird migrants

See allHide authors and affiliations

Science Advances  04 Jan 2017:
Vol. 3, no. 1, e1601360
DOI: 10.1126/sciadv.1601360
  • Fig. 1 Spatiotemporal distribution of individuals of three transhemispheric migrant bird species in relation to seasonal changes of absolute and local surplus vegetation greenness (NDVI) during the annual cycle.

    The map in the center shows the annual migration with general stopover areas of the common cuckoo, red-backed shrike, and thrush nightingale indicated in yellow, red, and blue lines, respectively. Maps compare patterns of greenness (maps on the left side; dark green, high average NDVI) and local surplus greenness (maps on the right side; dark gray, high average surplus NDVI) every 2 months from the breeding season (June) through changing species-specific nonbreeding stopover locations. Cuckoos (n = 8; stopovers shown in yellow) maximize absolute greenness, whereas shrikes and nightingales track local peak greenness (n = 18 and n = 12, respectively; stopovers in red and blue). (Monthly comparisons are shown in fig. S2.)

  • Fig. 2 Timing of individual birds in relation to the seasonal development of NDVI in specific stopovers.

    Each chart represents one of the major stopovers consistent among conspecific individuals. The black lines show the average NDVI over the course of a year on the average location of each stopover, and the bars show the percentage of conspecifics present in that stopover for at least 5 days in each biweekly period. Maps show the average location of the stopovers of cuckoos (yellow), red-backed shrikes (red), and thrush nightingales (blue).

  • Fig. 3 Greenness and surplus greenness along observed migratory tracks and comparisons with simulated tracks.

    (A) Expected biweekly values of vegetation greenness and (B) surplus greenness of the locations used during the annual cycle by common cuckoos (yellow lines), red-backed shrikes (red lines), and thrush nightingales (blue lines). The background shows the biweekly NDVI and surplus NDVI quantiles for the Eurasian-African area considered. (C to E) Comparison of vegetation experienced along simulated tracks. The number of latitudes traversed reflects wintering latitude; traversing 180° corresponds to wintering in southern Africa. (C) Average greenness, NDVI [ranging from 0 (no greenness) to 1 (maximum greenness)], (D) surplus NDVI (surplus greenness; a value of 1 corresponds to average local NDVI; a value higher than 1 indicates vegetation greener than the average), and (E) change in NDVI (from the previous biweekly period), as a function of the latitudes traversed for simulated random migratory tracks from southern Scandinavian breeding grounds (55°N, 13°E) compared to observed tracks of cuckoos (yellow), shrikes (red), and nightingales (blue). Tracks were simulated as round trips (south and back) with a variable realistic number of migratory steps (two to eight) of variable length summing up to total latitudes traversed. Lines mark the average, dark shading denotes the lower 95% quantile, and pale shading indicates the upper 5% quantile from random simulations. Average NDVI and surplus NDVI were considered measures of average absolute and average surplus vegetation greenness, respectively.

  • Fig. 4 Potential effects of future climate change on matching of resources along migratory tracks.

    Difference in projected (A) vegetation greenness, NDVI, and (B) vegetation surplus greenness, peak NDVI, along migratory tracks per month [1 (January) to 12 (December)] for 2011 and 2080 based on three climate change scenarios [26, 45, and 85 parts per billion (ppb) atmospheric CO2]. We used biweekly projected data on precipitation and temperature to model NDVI. Simulated tracks traversed 100° to 160° of latitudes in total (starting at 55°N, 9°E), corresponding to a trans-Saharan migration (indicated by the four gray lines). The differences between the projected vegetation greenness for tracks in 2011 and 2080 of common cuckoos (yellow lines) and projected surplus vegetation greenness for shrikes (red lines) and nightingales (blue lines) are shown for comparison with the simulated random tracks. Positive values indicate expected improvement of environmental conditions (NDVI and peak NDVI) by 2080, and negative values indicate impoverished conditions or a mismatch. Breeding season data are omitted because of aberrant projections due to a low proportion of land cover.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/1/e1601360/DC1

    fig. S1. Seasonal variation in NDVI across Africa and Europe.

    fig. S2. Patterns of greenness and surplus greenness for each month.

    fig. S3. Illustration of the random migratory track simulation procedure.

    fig. S4. Individual variation in experienced and expected greenness and surplus greenness along migratory tracks.

    fig. S5. Testing NDVI models.

    fig. S6. Sequence of monthly differences between 2011 and 2080 of ΔNDVI and Δsurplus NDVI based on the (a) 26 ppb, (b) 45 ppb, and (c) 85 ppb projected climate change scenarios and stopover positions of common cuckoos, red-backed shrikes, and thrush nightingales.

    fig. S7. Comparisons of current and modeled future NDVI and surplus NDVI for simulated tracks.

    data file S1. Spatiotemporal positions of common cuckoos, red-backed shrikes, and thrush nightingales included in the study.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Seasonal variation in NDVI across Africa and Europe.
    • fig. S2. Patterns of greenness and surplus greenness for each month.
    • fig. S3. Illustration of the random migratory track simulation procedure.
    • fig. S4. Individual variation in experienced and expected greenness and surplus greenness along migratory tracks.
    • fig. S5. Testing NDVI models.
    • fig. S6. Sequence of monthly differences between 2011 and 2080 of ΔNDVI and Δsurplus NDVI based on the (a) 26 ppb, (b) 45 ppb, and (c) 85 ppb projected climate change scenarios and stopover positions of common cuckoos, red-backed shrikes, and thrush nightingales.
    • fig. S7. Comparisons of current and modeled future NDVI and surplus NDVI for simulated tracks.
    • Legend for data file S1

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • data file S1 (Microsoft Excel format). Spatiotemporal positions of common cuckoos, red-backed shrikes, and thrush nightingales included in the study.

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article