WHERE TO WATCH?
an egg a day for almost a fortnight, but they don’t incubate them until the clutch is complete (or all but complete). That way the eggs all hatch on the same day, and all the chicks have a fair fight to survive as they beg their parents for a share. In the case of Jackdaws, if the female starts sitting after laying the second egg, it means that the first two eggs will be laid at least two days, and up to a week before the last egg. Since all Jackdaw eggs take about the same time to incubate, a Jackdaw brood will comprise youngsters of widely differing ages. In such broods, the oldest always have an unfair advantage when the adults come in with food; they are bigger, noisier and more insistent. If they are hungry, they always get fed first. In a year with plenty of food, the oldest nestlings will become satiated, and probably doze off, giving the younger chicks a chance to feed and put on weight. However, the strategy caters for bad years. If food is scarce, the older chicks will be fed but rarely become satiated, meaning that the younger birds might miss out entirely, and starve to death. In biological terms, however, it means that in bad years, at least one or two chicks will survive. If all the chicks had been fed equally in a bad year, they would probably all have starved. The other biological mechanism that suggests life isn’t easy for breeding Jackdaws is a very surprising one – monogamy. You might think that most birds are monogamous, and socially speaking they are. Male and female stick together for most, or all of the breeding attempt, and have defined roles. However, few birds are genetically monogamous; in 80% of species studied, there is at least some cuckoldry. Both males and females regularly copulate outside the social pair bond, the males to sow as many wild oats as possible and the females to acquire some genetic material from superior males. However, in Jackdaw society, neither males nor females stray outside the pair bond. They are one of the few birds in which genetic monogamy is the norm, with every egg in a clutch being fertilised by the resident male. You might conclude that their faithfulness is noble. But there is a sense in which Jackdaws are compelled to be monogamous. And, once again, it seems to be related to the difficulty of raising a brood. Jackdaws, it seems, need all hands to the pump when feeding young, which means that both male and female need to slog their guts out to make the enterprise successful. Owing to the fact that any egg laid by the female is by definition her own offspring, we can guarantee that she will feed young, secure in the knowledge that she is labouring for her own progeny. On the other hand, the male has no such assurances. Jackdaw colonies are full of fertile males and females at close quarters, and it would be quick and easy for any female to embark on an extrapair liaison. However, if the male has any doubts, he might withdraw his labour when providing for the young – and males of a number of species do just that when they suspect they have been cuckolded. It seems, then, that best practice for Jackdaws is never to embark on any relations outside the pair bond. It is too risky for any female to compromise the commitment of her partner. So monogamy is the rule. This, you might say, is hardly the happiest reason to be faithful to a partner. But then Jackdaws, as we’ve seen, don’t have the easiest time breeding. Now, though, it is all over. If birds felt relief, it might just be Jackdaws that are sighing the loudest. Jackdaws nest in cavities in trees, and, of course, chimney pots Could you resist feeding these demanding youngsters? SPECIES FACTFILE You’ll see Jackdaws any time of year in fields, woods, parks and gardens – they’re social birds and are common across the UK, except the Scottish Highlands. They’ll join Rooks and Carrion Crows to roost together in huge numbers.
Jackdaws, it seems, need all hands to the pump when feeding young, which means that both male and female need to slog their guts out to make the enterprise successful HOLE NESTERS FEED ME!