Bird Watching (UK) - - Species Jackdaw -

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!

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