NESTLING DIETS OF PRAIRIE PASSERINE BIRDS AT MATADOR, SASKATCHEWAN, CANADA

• Published in: Ibis
• Main Author: MAHER, WILLIAM J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1979
• Subjects: Eremophila alpestris
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1979.tb06684.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1979.tb06684.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1979.tb06684.x

SUMMARY The nestling diets of seven species of grassland passerines were studied from gullet samples collected in 1969–1971 at Matador, Saskatchewan, Canada. Relative population densities on census plots on grazed and ungrazed prairie showed that Horned Lark Eremophila alpestris , McCown's Longspur Calcarius mccownii and Chestnut‐collared Longspur C. ornatus preferred grazed areas and Sprague's Pipit Anthus spragueii , Western Meadowlark, Sturnella neglecta , Savannah Sparrow Passerculus sandwichensis and Baird's Sparrow Ammodramus bairdii preferred ungrazed prairie. Fifteen invertebrate ordinal taxa, and seeds were represented to an important extent in combined gullet contents; but two taxa, Lepidoptera (77% larvae) and grasshoppers (all Acrididae), comprised the bulk of nestling diets. Four grasshopper species contributed 70–100% of grasshoppers eaten in June‐August. Overlap at the family level was also high in several other important prey. Comparison with invertebrate populations of ungrazed prairie showed that the birds ignored some abundant taxa of very small invertebrates, and apparently preferred the two least abundant groups which offered large individual prey items. Average nestling food overlap indices for the season among all species except Savannah Sparrow and Baird's Sparrow, based on taxonomic composition, was 0.85. Overlap was moderate in May and June and became very high in July and August. The number of nestlings reached a peak in June and early July when nestling food overlap was much lower than later in the season. Horned Larks avoid competition by nesting earlier than do the other species, while McCown's Longspur, which depends on grasshoppers for nestling food more than do the other species, tends to breed later in the season than the other species. Finally, data suggest that nestling food may be superabundant.