Research ArticleAVIAN BIOLOGY

Trait-mediated trophic cascade creates enemy-free space for nesting hummingbirds

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Science Advances  04 Sep 2015:
Vol. 1, no. 8, e1500310
DOI: 10.1126/sciadv.1500310
  • Fig. 1 Video-grab of a Mexican Jay removing the eggs from the nest (middle-lower right) of black-chinned hummingbird.
  • Fig. 2 Stylized graphical model of cone-shaped space surrounding active hawk nests, within which hummingbird nests had significantly higher survivorship.

    Data on the locations of jays in relation to each plot’s hawk nest were pooled across plots and were used to generate the shape of the cone, using the lowest individual jays detected during the study and superimposed on a fictional landscape representative of the study area. Yellow, hawk nest; green, successful hummingbird nest; red, depredated hummingbird nest.

  • Fig. 3 Interannual comparisons of jay foraging patterns in study plots, illustrating the effect of raptor presence on the spatial distributions of foraging jays.

    Each point represents the mean height above the ground of individual jays within a single flock. Plots with active hawk nests are shaded gray. Upper panels show pooled data from two plots that were occupied in both years, middle panels represent four plots that were not reoccupied in 2009, and bottom panels show one plot occupied for the first time in 2009. ANCOVA with all plots and years combined revealed a significant interaction (F1, 341 = 36.4; P < 0.0001) between distance to a raptor nest and activity of the raptor (presence/absence). Plots that were unoccupied for the duration of the study are not illustrated.

  • Fig. 4 Path analysis results (model fit χ2 = 3.6; df = 4; P = 0.46) for the proposed causal relationships between raptor presence, jay foraging height, and hummingbird responses.

    “Hawk affinity” was measured as distance to the hawk nest; “hummingbird dispersion” was a measure of dispersion determined using the nearest-neighbor value, R (larger values indicate less clumping); “hummingbird nest survival” was the daily survival rate (DSR). Arrows indicate positive causal relationships; the bullet-headed line indicates a negative causal relationship. Numbers next to lines are significant path coefficients (*P < 0.05, **P < 0.001). The path coefficient from hummingbird dispersion to survival was small (0.01) and not significant (P > 0.6); thus, the model fit was improved when it was excluded. An identical model using jay dispersion instead of hummingbird dispersion was a poor fit to the data (model significantly different from the data: χ2 = 15.5; df = 4; P = 0.004).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/8/e1500310/DC1

    Methods and Analyses

    Fig. S1. Cone-shaped enemy-free space surrounding three representative active hawk nests.

    Fig. S2. Photo of a hummingbird nest in situ showing variables measured to quantify nest microsite selection.

    Fig. S3. Diagrammatic illustration of variables measured at each hummingbird nest to quantify nest site selection within the substrate tree.

    Table S1. A review of the literature on protective nesting associations in birds indicating the species involved (if known) and the hypothesized mechanism by which the protected species benefits.

    References (2866)

  • Supplementary Materials

    This PDF file includes:

    • Methods and Analyses
    • Fig. S1. Cone-shaped enemy-free space surrounding three representative active hawk nests.
    • Fig. S2. Photo of a hummingbird nest in situ showing variables measured to quantify nest microsite selection.
    • Fig. S3. Diagrammatic illustration of variables measured at each hummingbird nest to quantify nest site selection within the substrate tree.
    • Table S1. A review of the literature on protective nesting associations in birds indicating the species involved (if known) and the hypothesized mechanism by which the protected species benefits.
    • References (28–66)

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