SimonR wrote: ↑Sun May 01, 2022 4:34 pm
Bought some live mealworms today as an extra treat for the fledglings. The parents have been ferrying them into the greenhouse.
They are probably old enough and have active-enough guts, but brown mealworms are EXTREMELY difficult for nestlings to digest - they cannot break the tough brown skins, so the mealworms are usually passed as eaten, just dead. Freshly-moulted (white) mealworms have a far better chance of being digested.
Softbills (non-seedeaters) feed live food as is, hardbills (seedeaters) generally pulp live food before feeding it to nestlings.
Davey246 wrote: ↑Sun May 01, 2022 10:32 am
Sheds and such seem far more attractive to robins than any nestbox. I have had a very occasional nest in a box here, but in over 20 years, it has been rare. The two or three pairs that have territories that meet in my garden each year, rear young - different birds can be watched as they carry off beakfuls of bugs in totaly different directions.
That's very interesting. I've always thought that Robins were fiercely territorial. But there seems to be two pairs feeding in my garden and then heading off in opposite directions back to their nests. I haven't seen any fights. They all seem to get on well.
The fledglings are abound the last few days. Surprisingly they look bigger that the parents, who are worn to a frazzle from feeding them.
I also have a Robin box up, which they ignore. But if I leave the workshop door open they're in building like a shot despite the fact that I lock it every evening.
Robins are extremely, fiercely territorial, but a border has to exist between territories somewhere, and that is obviously in your garden.
Probably two additional things influence the lack of obvious agression - your garden is a good source of food (quite something if the weather with you has been as here - VERY dry until the past 3 days), and presumably reasonably large, and there isn't time to fight while rearing chicks.
There are also hormonal changes in males that reduce aggression when there is the stimulus of gaping mouths begging to be fed. The breeding season for something like a male robin goes from agressive aquisition of territory, change to nest-building and feeding of hen, change to defence of territory while the hen incubates, change to feeding of chicks, and then moult will usually kick in. All controlled by 2? 3? hormones ebbing and flowing.
The chicks should disperse, which reduces risk of total loss due to predation and/or bad weather, and the border will probably blur some more.
Many nidicolous birds leave the nest slightly heavier than parents - a sort of insurance for the next dangerous step in life. Certainly a lot of passerine nestlings also leave the nest rather "fluffy", which makes them look bigger.
It's interesting to read the comments in this thread. Every year for over 54 years we have had robins nesting in sheds and greenhouses on my father's property in a rural Hampshire village (at least 2 nesting pairs every year since he moved there). Never have we had more than 4 fledglings, and the average over those years has been 3. Some of the higher numbers quoted seem unlikely from our lengthy experience. So far this year we have had just 2 fledglings from a random wooden box in a large greenhouse (110ft X 40ft), and 3 from a smaller garden shed. Second broods in years past have generally been of a similar size, and we look forward to being entertained by them in the coming weeks.
David Neville
Secretary of Southampton & District Branch. BCSS member since 1977.
Weird!
I would say that the great majority of nests that I have known have been 4 eggs and clear eggs and nestling mortality have been rare to the extent that they have been almost unknown.
Fledgling mortality will be close to 100%. If it were not, the population would be growing at a prodigious rate - simple maths and fact of life.
Maybe a wetter climate making bugs more easily won for rearing?
Ignoring the tiny number of nests in boxes here, and those in sheds, etc. of friends and aquaintances, over the 60 years that I have been "nesting" (as in keeping a keen eye out for bird nests of any kind), I have found 4 robin's nests.
The first was when I went for a pee against a hedge and noticed something odd in a paint tin that had been thrown into the hedge - I would have been 4-5-6-7 years old. The others were in the roof lining of a VERY old car that was on the verge of rusting away/collapsing, another inside a relatively vast hole within a hollow willow - the birds had made a nest in a scrape in the leafmould/frass/decomposed wood in the bottom, and few years ago, they nested in a christmas tree that I'd leant against the compost heap, prior to it being chipped.
Yes fledgling mortality is depressing high here in Hampshire! Pet cats, magpies and jays are the 3 main culprits in our experience. But we have also found fledglings drowned in fishponds, buckets, and virtually any other water containers you can imagine over the years. Fledglings are definitely not born with common sense.... It takes them a while to acquire it!
David Neville
Secretary of Southampton & District Branch. BCSS member since 1977.
Next in the list of fledgling murderers is definitely Sparrowhawks, which are common here. They frequently kill and pluck numerous small birds and finches even on domestic gardens and lawns in my area, and then either consume or feed any gains to their nested offspring!, Frequently plucking their prey in the garden before carrying it to their offsprinng frequently upsets my neighbours....
David Neville
Secretary of Southampton & District Branch. BCSS member since 1977.
Nature is red in tooth and claw. Fact.
BUT, for every fledgling, a bird has to die before the following breeding season if populations are to remain stable. Very simple maths.
There are a few papers online that look at post-fledging populations in a whole variety of bird species, and the ones that I have found are amazingly consistent - in the average year, the number of any species, post fledging, is around twice the number of the population at the start of that breeding season - clutch and brood size count for not much at all. So post fledging to start of the following breeding season there is, on avergae, 50% mortality.
I haven't looked in a while, but the last time that I looked at figures for UK ospreys - guess what? AROUND double the number of birds went south each autumn as had migrated here in spring. The next spring, the number arriving was AROUND 10% more than had arrived the previous spring - around 45% of the birds that left the previous autumn, had died.
This will have been affected by weather etc. but also by how many breeding territories were available - few available and there would be non-breeders. This was "fixed" by trans-locating birds outside where learned migration would have taken them - in effect generating extra breeding territories extra quick.
Sarrowhawks? As I grew up their numbers went from vanishingly few (probably part of the DDT debacle), to uncommon. They are now common. I hate them when they take larger prey - blackbirds and collared doves usually, around here - they very, very seldom kill them out-right. Hearing and/or seeing either being ripped apart and eaten alive is not for the feint-hearted. I have even watched as a spar has clung onto a leylandii and grappled with a huge wood-pigeon squab in a nest in the conifer - it was FAR too heavy for the spar to carry anywhere but downwards. Gruesome.
Davey
Gruesome .... is the only word. And .... red in tooth and claw ..... the only descriptor.
For that reason .... I don't watch natural history programmes .... but I know that the mathematics is crucial to the balance in nature, both for predator and prey.
Endeavouring to grow Aylostera, Echinocereus, Echinopsis, Gymnocalycium, Matucana, Rebutia, and Sulcorebutia. Fallen out of love with Lithops and aggravated by Aeoniums.
Currently being wooed by Haworthia, attempting hybridisation, and enticed by Mesembs.
It is always worth bearing in mind that, if you take man the predator out of the equation, in undisturbed ecosystems, predation very very rarely has a measuarable effect on prey numbers. In the vast majority of cases natural events - disease, weather, lack of food, lack of space for a home territory (and how these interplay) - are the biggest killers, usually by far.
