Do helpers really help? Provisioning biomass and prey type effects on nestling growth in the cooperative bell miner

Luc te Marvelde, Paul G. McDonald*, Anahita J N Kazem, Jonathan Wright

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)

Abstract

Provisioning visits by helpers are normally assumed to confer positive fitness effects on nestlings, but few studies have actually examined the nutritional value of items helpers fed to offspring. In the cooperatively breeding bell miner, Manorina melanophrys, helpers deliver large proportions of 'lerp', a sugary secretion of psyllids (Hemiptera; Psyllidae). Although lerp is a major food type of adults, its nutritional value is uncertain, especially since nestlings in other nectarivorous species are usually fed only protein-rich arthropods. Helpers in this system are predominantly male and are often unrelated to broods they aid, suggesting helping might be a sexual display, with any nutritional benefits to nestlings being of secondary importance. Detailed observations revealed that the proportion of lerp delivered increased with nestling age, but that it did not differ between helpers and parents, or between related and unrelated helpers. Variation in delivered biomass (lerp+arthropods) had a positive effect on nestling condition, but variation in the proportion of prey constituted by lerp had no measurable effect on nestling mass or condition. Finally, the total amount of food, nestling body mass and condition were all positively related to the number of helpers provisioning broods. These results are consistent with helping in bell miners operating as cooperative investment in brood fitness. Given that lerp was as effective as invertebrate prey in promoting growth, these results also suggest a valid nutritional role for this easily procured food, presumably facilitated by the unusually early development of nestling digestive tracts to utilize these simple sugars.

Original languageEnglish
Pages (from-to)727-735
Number of pages9
JournalAnimal Behaviour
Volume77
Issue number3
DOIs
Publication statusPublished - Mar 2009

Keywords

  • bell miner
  • digestive development
  • group augmentation
  • helping at the nest
  • kin selection
  • Manorina melanophrys
  • nestling growth

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