Every spring our residential  rooks and crows are getting excited, building beautiful nests and are laying eggs. Unfortunately, we then have to replace these eggs with dummy eggs, as we do not intend to let them raise unreleasable offspring in captivity. However, we encourage our birds in doing so, as it is part of their normal natural behaviour and life cycle, by providing them with all the nesting materials and nutrients required. All birds then sit on their eggs, with food being provided by their respective partners, until they eventually realise that their brood has failed.

Most rooks and less commonly crows will at some point discard most of the failed eggs, and will then add selected toys from their enrichment reservoir in to their nest. They will eventually cover remaining eggs and toys with moos and soft nesting material. Both will remain mostly untouched for about two to three weeks. That is the moment when their grieving period starts…

Based on research into rook behaviour, it appears that wild rooks do exhibit this tendency too. Rooks are highly intelligent corvids known for their complex nesting habits and cognitive abilities. When a breeding season fails, they often do not immediately discard the nest contents or the site itself. Instead, they may retain various objects, such as twigs, moss or even small non-nesting items they had gathered within the nest structure.

There is evidence suggesting that these birds may re-engage with these objects later in what observers describe as playful manipulation or caching behaviour. This suggests a level of object permanence and a likely intrinsic interest in manipulating materials beyond immediate survival needs. Rather than abandoning the nest entirely after failure, rooks might keep these items, potentially reusing them if they attempt to breed again or simply interacting with them as part of their natural behavioural repertoire.

This behaviour aligns with broader observations of corvid intelligence, where object play and caching are well documented traits, indicating that for rooks and crows the nest can serve not just as a reproductive site but also as a repository for interesting or even memorable objects.

Research indicates that when rook broods fail in the wild both parents often exhibit several notable behavioural changes. They remain at or near the empty nest for extended periods rather than immediately abandoning it. Both male and female may stay together for days or weeks. Parents continue behaviours,  typically directed at live chicks, such as soft, repetitive calls, gentle nudging of the nest cup and attempts to brood the spot where chicks were.

It has been also seen that their foraging activity decreases noticeably. Overall activity levels appear reduced, described by some observers as lethargic or depressed. These patterns can last from several days to a couple of weeks before the birds move on.

The behaviour of keeping play objects in the nest fits within this broader picture but remains less documented than the other behavioural changes. It could represent part of a continued nest-related focus, but in our view and experience it is very likely a coping mechanism through object manipulation.

Despite lacking a neocortex, which is the mammalian brain region linked to higher cognition, corvids have densely packed neurons in their pallium, which is the avian analog. This compact structure supports rapid information processing, flexible decision-making and emotional regulation, which does explain grief-like behaviours. Interestingly, studies suggest their brain-to-body ratio rivals that of primates, supporting similar levels of abstract thought despite evolutionary divergence.

Given this cognitive framework, the behaviour of keeping play objects post brood failure becomes more meaningful. Rooks understand that unseen objects exist, a trait shared only with primates. Keeping items reflects continued engagement with familiar stimuli during distress. Corvids seem to possess neural circuits for empathy and  attachment, which means that retaining nesting materials may serve as comfort or ritualistic processing akin to human mourning traditions involving heirlooms.