Diurnal foraging-mode shifts and food availability in nectarivore assemblages during winter

C.A.R. Timewell, R. Mac Nally

    Research output: Contribution to journalArticle

    24 Citations (Scopus)

    Abstract

    Temporal fluctuations of food resources and foraging activities have been studied extensively, especially at longer timescales (monthly, seasonally, among years). However, short-term variation (e.g. within days) is less well understood. Here we systematically quantified diurnal patterns of foraging by nectarivorous birds (meliphagid honeyeaters) that numerically dominated stands of a winter-flowering eucalypt, the red ironbark, Eucalyptus tricarpa, in central Victoria, Australia. Diurnal variation in food resources also was measured. Data were collected in winter. Anecdotal observations that honeyeaters change from almost exclusive nectarivory early in the day to a higher fraction of insectivory – especially aerial hawking – later in the day were confirmed, although in areas of high flowering intensity, nectar-feeding remained the dominant foraging activity throughout the day. Local climatic factors (ambient temperature, windiness and cloud cover) all varied systematically through the day. Together, results were consistent with a change in foraging emphasis to greater insectivory as a function of elevated activities of insects (especially aerial ones), which was probably fostered by higher ambient temperatures. Contrary to energetic expectations, the nectarivores were very active early in the morning when ambient temperatures averaged approximately 3°C, well below thermoneutral temperatures. We deduced that the potential benefits of gathering as much energy-rich nectar as possible before it was depleted outweighed the high costs of activities at low temperatures.
    Original languageEnglish
    Pages (from-to)264-277
    Number of pages14
    JournalAustral Ecology
    Volume29
    Issue number3
    DOIs
    Publication statusPublished - 2004

    Fingerprint

    nectar feeding
    food availability
    insectivory
    foraging
    ambient temperature
    insectivores
    winter
    nectar
    diurnal variation
    flowering
    nectarivory
    Eucalyptus sideroxylon
    Victoria (Australia)
    temperature
    food
    climatic factors
    resource
    cloud cover
    Eucalyptus
    energetics

    Cite this

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    abstract = "Temporal fluctuations of food resources and foraging activities have been studied extensively, especially at longer timescales (monthly, seasonally, among years). However, short-term variation (e.g. within days) is less well understood. Here we systematically quantified diurnal patterns of foraging by nectarivorous birds (meliphagid honeyeaters) that numerically dominated stands of a winter-flowering eucalypt, the red ironbark, Eucalyptus tricarpa, in central Victoria, Australia. Diurnal variation in food resources also was measured. Data were collected in winter. Anecdotal observations that honeyeaters change from almost exclusive nectarivory early in the day to a higher fraction of insectivory – especially aerial hawking – later in the day were confirmed, although in areas of high flowering intensity, nectar-feeding remained the dominant foraging activity throughout the day. Local climatic factors (ambient temperature, windiness and cloud cover) all varied systematically through the day. Together, results were consistent with a change in foraging emphasis to greater insectivory as a function of elevated activities of insects (especially aerial ones), which was probably fostered by higher ambient temperatures. Contrary to energetic expectations, the nectarivores were very active early in the morning when ambient temperatures averaged approximately 3°C, well below thermoneutral temperatures. We deduced that the potential benefits of gathering as much energy-rich nectar as possible before it was depleted outweighed the high costs of activities at low temperatures.",
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    Diurnal foraging-mode shifts and food availability in nectarivore assemblages during winter. / Timewell, C.A.R.; Mac Nally, R.

    In: Austral Ecology, Vol. 29, No. 3, 2004, p. 264-277.

    Research output: Contribution to journalArticle

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