Browsing by Author "Cockle, Kristina"

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    Complex dynamics of tree cavities and nest webs in the Americas
    (2018) Cockle, Kristina; Ibarra Eliessetch, José Tomás; Trzcinski, Kurtis; Wiebe, Karen L.; Altamirano Oyarzún, Tomás Alberto; Edworthy, Amanda; Martin, Kathy
    The Nest Web concept represents tree-cavity-nesting communities as hierarchical, commensal networks, whereby nesting cavities flow upward from trees to cavity producers (e.g., woodpeckers, decay organisms) to a diverse assemblage of non-excavators (e.g., parrots, songbirds). These nest webs are dynamic, complex, and often resilient. They include non-hierarchical feedback loops, such as facultative excavation, inter-guild predation and competition. For >20 years we studied >4000 nesting cavities in temperate British Columbia, Canada (1995-2016), temperate Chile (2010-2018) and subtropical Argentina (2006-2018), to examine the dynamics of cavity-nesting communities over time, at scales from individual cavities to whole nest webs. Individual cavities in large old-growth trees persisted longest. Cavities became larger as they aged, and were occupied by a succession of vertebrates (excavators, then small-bodied non-excavators, and finally largebodied non-excavators). Cavities produced 0–43 fledglings/cavity over their lifetime, but cavities with higher nest success were occupied fewer times by fewer species. At the nest web scale in Canada, an abundant facultative excavator declined in importance in the Nest Web during an insect outbreak that attracted obligate excavators, but then dramatically increased cavity production following wildfires. Logging resulted in disproportional biodiversity losses when it targeted key network hubs (large trees; Chile, Argentina) but not when a critical nesting tree species was retained (Canada). A nest web approach helped us understand interspecific interactions and test network theory; because these networks are strongly influenced by outside sources of uncertainty and non-linearity, a Complex Systems Science approach may improve predictions about their long-term dynamics
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    Latitude does not influence cavity entrance orientation of South American avian excavators
    (OXFORD UNIV PRESS INC, 2021) Ojeda, Valeria; Schaaf, Alejandro; Altamirano, Tomas A.; Bonaparte, Bianca; Bragagnolo, Laura; Chazarreta, Laura; Cockle, Kristina; Dias, Raphael; Di Sallo, Facundo; Ibarra Eliessetch, José Tomás; Ippi, Silvina; Jauregui, Adrian; Jimenez, Jaime E.; Lammertink, Martjan; Lopez, Fernando; Montellano, Maria Gabriela Nunez; de la Pena, Martin; Rivera, Luis; Vivanco, Constanza; Santillan, Miguel; Soto, Gerardo E.; Vergara, Pablo M.; Wynia, Amy; Politi, Natalia
    In the Northern Hemisphere, several avian cavity excavators (e.g., woodpeckers) orient their cavities increasingly toward the equator as latitude increases (i.e. farther north), and it is proposed that they do so to take advantage of incident solar radiation at their nests. If latitude is a key driver of cavity orientations globally, this pattern should extend to the Southern Hemisphere. Here, we test the prediction that cavities are oriented increasingly northward at higher (i.e. colder) latitudes in the Southern Hemisphere and describe the preferred entrance direction(s) of 1,501 cavities excavated by 25 avian species (n = 22 Picidae, 2 Trogonidae, 1 Furnariidae) across 12 terrestrial ecoregions (15 degrees S to 55 degrees S) in South America. We used Bayesian projected normal mixed-effects models for circular data to examine the influence of latitude, and potential confounding factors, on cavity orientation. Also, a probability model-selection procedure was used to simultaneously examine multiple orientation hypotheses in each ecoregion to explore underlying cavity-orientation patterns. Contrary to predictions, and patterns from the Northern Hemisphere, birds did not orient their cavities more toward the equator with increasing latitude, suggesting that latitude may not be an important underlying selective force shaping excavation behavior in South America. Moreover, unimodal cavity-entrance orientations were not frequent among the ecoregions analyzed (only in 4 ecoregions), whereas bimodal (in 5 ecoregions) or uniform (in 3 ecoregions) orientations were also present, although many of these patterns were not very clear. Our results highlight the need to include data from under-studied biotas and regions to improve inferences at macroecological scales. Furthermore, we suggest a re-analysis of Northern Hemisphere cavity orientation patterns using a multi-model approach, and a more comprehensive assessment of the role of environmental factors as drivers of cavity orientation at different spatial scales in both hemispheres.
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    Variation in the role of tree decay to promote cavity nester biodiversity in the World Wide Cavity Nest Web
    (2014) Martin, Kathy; Ibarra Eliessetch, José Tomás; Cockle, Kristina; Altamirano Oyarzún, Tomás Alberto
    From a biodiversity perspective, much of the world is chronically short of tree decay, especiallyin human-influenced ecosystems. Yet over 1000 bird species globally depend on decay processesto form tree cavities to provide the critical nesting and roosting sites. Cavities can form slowlyover centuries with the presence of tree decay or physical processes or they may form relativelyquickly when avian excavators penetrate the outer sapwood and remove the decayed heartwood.We examine the role of tree decay dynamics in structuring cavity-using vertebrate communitiesin Nest Webs (i.e., interdependent assemblages of cavity consumers and/or producers instructured-nidic guilds) across continents in temperate and tropical systems in the Americas andAfrica. In the Nest Webs of North-America, woodpeckers function as keystone species as theyexcavate over 90% of the holes used by secondary cavity nesting (non-excavating) vertebrates.In South-America, 69-80% of secondary cavity nesters use cavities formed by decay or externaldamage, even when woodpeckers are present. The abundance and diversity of cavity-usingvertebrates is often positively associated with cavity availability that in turn depends on rates ofhole formation and persistence. To maintain biodiversity it is critical to understand the role oftree decay and excavators as structuring agents in wildlife communities. In North America, thisinvolves retaining the tree types and conditions (e.g., hard deciduous trees with soft spots ofdecay) that are suitable for woodpeckers to excavate. In forest ecosystems with decay-based nestwebs (South-America, Africa), it is important to retain a supply of large live trees with decayed branches and large and small dead-standing trees to maintain a diversity and abundance ofcavity-using birds.