How important is nectar in shaping spatial variation in the abundance of temperate breeding hummingbirds?

Feldman, Richard E.; McGill, Brian J.

doi:10.1111/jbi.12226

Cited by 14 publications

(17 citation statements)

References 53 publications

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“…Other guilds for which models based on short-term variability and long-term climate averages performed equally well included waterbird invertivores and water foragers, floral hoverers, and bark foragers. During the breeding season, occurrences of floral hover species may be less tied to nectar resources influenced by weather and more to local habitat characteristics and presence of conspecifics (Feldman and McGill 2013). Bark foragers have a food source that is available throughout the annual cycle (Vermunt et al 2012), and all of these species are permanent residents.…”

Section: Discussionmentioning

confidence: 99%

Potential breeding distributions of U.S. birds predicted with both short‐term variability and long‐term average climate data

Bateman

Pidgeon

Radeloff

et al. 2016

Ecological Applications

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Climate conditions, such as temperature or precipitation, averaged over several decades strongly affect species distributions, as evidenced by experimental results and a plethora of models demonstrating statistical relations between species occurrences and long-term climate averages. However, long-term averages can conceal climate changes that have occurred in recent decades and may not capture actual species occurrence well because the distributions of species, especially at the edges of their range, are typically dynamic and may respond strongly to short-term climate variability. Our goal here was to test whether bird occurrence models can be predicted by either covariates based on short-term climate variability or on long-term climate averages. We parameterized species distribution models (SDMs) based on either short-term variability or long-term average climate covariates for 320 bird species in the conterminous USA and tested whether any life-history trait-based guilds were particularly sensitive to short-term conditions. Models including short-term climate variability performed well based on their cross-validated area-under-the-curve AUC score (0.85), as did models based on long-term climate averages (0.84). Similarly, both models performed well compared to independent presence/absence data from the North American Breeding Bird Survey (independent AUC of 0.89 and 0.90, respectively). However, models based on short-term variability covariates more accurately classified true absences for most species (73% of true absences classified within the lowest quarter of environmental suitability vs. 68%). In addition, they have the advantage that they can reveal the dynamic relationship between species and their environment because they capture the spatial fluctuations of species potential breeding distributions. With this information, we can identify which species and guilds are sensitive to climate variability, identify sites of high conservation value where climate variability is low, and assess how species' potential distributions may have already shifted due recent climate change. However, long-term climate averages require less data and processing time and may be more readily available for some areas of interest. Where data on short-term climate variability are not available, long-term climate information is a sufficient predictor of species distributions in many cases. However, short-term climate variability data may provide information not captured with long-term climate data for use in SDMs.

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Section: Discussionmentioning

confidence: 99%

Potential breeding distributions of U.S. birds predicted with both short‐term variability and long‐term average climate data

Bateman

Pidgeon

Radeloff

et al. 2016

Ecological Applications

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“…Consequently, nectarivorous birds aggregate and attempt to breed where nectar resources are abundant (Ford , Calf et al ). Nonetheless, local environmental conditions, for instance those related to elevation and temperature, may also influence the number of nectarivorous birds at a site (Feldman and McGill ). Feldman and McGill () reported only weak relationship between abundance of nectar resources and hummingbird populations.…”

Section: Discussionmentioning

confidence: 99%

“…Nonetheless, local environmental conditions, for instance those related to elevation and temperature, may also influence the number of nectarivorous birds at a site (Feldman and McGill ). Feldman and McGill () reported only weak relationship between abundance of nectar resources and hummingbird populations. The effect of floral resources on birds may indeed vary among years (Herrera ) and bird species (Mulwa et al ).…”

Section: Discussionmentioning

confidence: 99%

“…Table 2 gives effect sizes of all predictors for the radial distances of 1 and 40 m, respectively. Feldman and McGill (2014) reported only weak relationship between abundance of nectar resources and hummingbird populations. The effect of floral resources on birds may indeed vary among years (Herrera 1998) and bird species (Mulwa et al 2013).…”

Section: Avian Populationsmentioning

confidence: 95%

“…However, pollinator abundance may not increase proportionally to the resource density provided by a plant community. A decrease in the pollinator to resource ratio may emerge because the size of the pollinator population is constrained by other environmental factors (Donaldson and Nänni , Feldman and McGill ) or influenced by competition among pollinators (Ford and Paton , Smith‐Ramirez and Armesto , Mac Nally and Timewell ). Under such circumstances, the pollination services are shared among more plants within a community (Goulson ) and pollinators become more selective in their visits to plants (Schmitt ), directing their foraging movements toward resource ‘hotspots’ within plant communities.…”

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confidence: 99%

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Responses of nectar‐feeding birds to floral resources at multiple spatial scales

et al. 2015

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The responses of animal pollinators to the spatially heterogeneous distribution of floral resources are important for plant reproduction, especially in species‐rich plant communities. We explore how responses of pollinators to floral resources varied across multiple spatial scales and studied the responses of two nectarivorous bird species (Cape sugarbird Promerops cafer, orange‐breasted sunbird Anthobaphes violacea) to resource distributions provided by communities of co‐flowering Protea species (Proteaceae) in South African fynbos. We used highly resolved maps of about 125 000 Protea plants at 27 sites and estimated the seasonal dynamics of standing crop of nectar sugar for each plant to describe the spatiotemporal distribution of floral resources. We recorded avian population sizes and the rates of bird visits to > 1300 focal plants to assess the responses of nectarivorous birds to floral resources at different spatial scales. The population sizes of the two bird species responded positively to the amount of sugar resources at the site scale. Within sites, the effects of floral resources on pollinator visits to plants varied across scales and depended on the resources provided by individual plants. At large scales (radii > 25 m around focal plants), high sugar density decreased per‐plant visitation rates, i.e. plants competed for animal pollinators. At small scales (radii < 5 m around focal plants), we observed either competition or facilitation for pollinators between plants, depending on the sugar amount offered by individual focal plants. In plants with copious sugar, per‐plant visitation rates increased with increasing local sugar density, but visitation rates decreased in plants with little sugar. Our study underlines the importance of scale‐dependent responses of pollinators to floral resources and reveals that pollinators’ responses depend on the interplay between individual floral resources and local resource neighbourhood.

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Winter conditions influence biological responses of migrating hummingbirds

et al. 2016

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Abstract. Conserving biological diversity given ongoing environmental changes requires the knowledge of how organisms respond biologically to these changes; however, we rarely have this information. This data deficiency can be addressed with coordinated monitoring programs that provide field data across temporal and spatial scales and with process-based models, which provide a method for predicting how species, in particular migrating species that face different conditions across their range, will respond to climate change. We evaluate whether environmental conditions in the wintering grounds of broad-tailed hummingbirds influence physiological and behavioral attributes of their migration. To quantify winter ground conditions, we used operative temperature as a proxy for physiological constraint, and precipitation and the normalized difference vegetation index (NDVI) as surrogates of resource availability. We measured four biological response variables: molt stage, timing of arrival at stopover sites, body mass, and fat. Consistent with our predictions, we found that birds migrating north were in earlier stages of molt and arrived at stopover sites later when NDVI was low. These results indicate that wintering conditions impact the timing and condition of birds as they migrate north. In addition, our results suggest that biologically informed environmental surrogates provide a valuable tool for predicting how climate variability across years influences the animal populations.

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How important is nectar in shaping spatial variation in the abundance of temperate breeding hummingbirds?

Cited by 14 publications

References 53 publications

Potential breeding distributions of U.S. birds predicted with both short‐term variability and long‐term average climate data

Potential breeding distributions of U.S. birds predicted with both short‐term variability and long‐term average climate data

Responses of nectar‐feeding birds to floral resources at multiple spatial scales

Winter conditions influence biological responses of migrating hummingbirds

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