Shrikes are well known for keeping larders of prey, such as large insects and small reptiles, by impaling them on thorny bushes or wires. Scientists have argued over the function of these stores, some suggesting they provide a backup resource during periods of poor food availability, while it has also been suggested that larders are a signal of territory quality by male birds.
Red-backed Shrikes mainly keep larders while they have young in the nest, instead of before breeding as in most other shrikes, which tempted researchers to investigate whether pairs with these food stores produced healthier young than those without such a stockpile.
Red-backed Shrike territories with larders produced young with higher haemoglobin levels than those without the back-up supply of food (Richard Mills).
Scientists monitored 20 Red-backed Shrike nests near Siedlce in east-central Poland. They found nine nests attended by pairs with larders and 11 without. Blood tests of the chicks showed that nestlings of larder-keeping parents had high haemoglobin levels overall, suggesting good body condition thanks to more reliable food deliveries.
Meanwhile, nestlings whose parents did not have larders had higher white blood cell counts, which is a sign of stress or infection.
The researchers concluded that their findings support the hypothesis that Red-backed Shrikes use larders as a 'safety net' food supply while raising young, ensuring a steady food supply during the nestling stage. Larders could also function as a signal of quality or a backup food supply for adult birds when prey becomes scarce.
Golawski, A, & Kondera, E. 2023. Storing prey in larders affects nestling haematological condition in the Red-backed Shrike (Lanius collurio). DOI: https://doi.org/10.1111/ibi.13104