Storing prey in larders affects nestling haematological condition in the Red‐backed Shrike (Lanius collurio)

Abstract

Many animals, including shrikes (Laniidae), are known to store food. This behaviour ensures food availability during inclement weather, for rearing nestlings or signalling territory quality. Unlike most other shrike species, which accumulate food before breeding, Red‐backed Shrikes Lanius collurio store food in larders, mainly during the nestling and fledgling periods. If this is an adaptive behaviour, variation in this behaviour should affect either or both the number and condition of nestlings, which may benefit from such larders. We assessed the haematological condition of Red‐backed Shrike nestlings in east‐central Poland in 2021 using a suite of blood parameters relating to sites where shrikes did or did not store food. Haemoglobin concentrations were positively correlated with larders, being significantly higher in nestlings of pairs that stored prey compared with those whose parents did not do so. White blood cell counts were lower in nestlings whose parents kept larders. Red blood cell counts and glucose concentrations in nestlings were not related to whether parents had larders. Food storage probably ensures a more constant access to food, which results in a superior haematological condition in nestlings.

Delayed egg-laying in Red-backed Shrike Lanius collurio in relation to increased rainfall in east-central Poland

“…Moreover, birds adjust their breeding season to the greatest availability of food when they are feeding their young (Both et al 2006). A cooler and rainier spring means that insects develop later, especially orthopterans, which are a very important component of the shrikes' diet in this region (Morelli et al 2016;Golawski and Kondera 2023), so this (Lack 1968); there will also be fewer renesting opportunities (Halupka et al 2008). Red-backed Shrikes can re-nest if the first brood is lost, but this depends on the period of the breeding season when that loss occurred (Antczak et al 2009), so later nesting can make a big difference to them.…”

“…Moreover, birds adjust their breeding season to the greatest availability of food when they are feeding their young (Both et al 2006 ). A cooler and rainier spring means that insects develop later, especially orthopterans, which are a very important component of the shrikes’ diet in this region (Morelli et al 2016 ; Golawski and Kondera 2023 ), so this may be a reason for the delay in clutch initiation. Delayed nesting can have serious consequences for birds, because females laying later in a given breeding season produce smaller clutches (Lack 1968 ); there will also be fewer re-nesting opportunities (Halupka et al 2008 ).…”