BOXING CLEVER
Nestbox cameras are giving us extraordinary insights into the secret lives of great tits. Kate Risely investigates.
Bold and colourful in personality and appearance, the great tit is one of the most spectacular animals to be overlooked by us all on a daily basis. It is also one of our most widespread birds and an estimated five million breed across the UK. The species is absent only from treeless Scottish islands, and concentrated in lowland, wooded areas of central and southern England. Here they form part of the background tapestry of our lives, and in the best habitats – rich deciduous woodland with plenty of nest sites – they can reach densities of over 300 breeding pairs per square kilometre.
Wildlife photographer David Tipling owns a small wood (100m by 150m) in North Norfolk, which he is managing with the twin aims of enhancing its wildlife value, and creating opportunities to get to know and photograph the resident wildlife. It could support over 30 pairs of great tits in perfect conditions. David has put up 15 nestboxes, which are occupied every year by a mixture of blue tits and great tits – a healthy population for the size of the wood.
One of the boxes is custom-made for photography, with a glass dividing wall inside the box providing space for a remotely operated camera. In the spring of 2016, the boxes in the wood were occupied as normal, with a great tit pair taking up residence in the modified camera-box. However, the weather was to prove disastrous for blue and great tit nesting attempts up and down the country. Spells of cold, wet weather hit at the end of May and early June, right at the time when these birds were nesting.
In David’s wood, one by one, the nests were abandoned, and he was worried about the birds in the camera-box: “I’ve monitored nests many times before, and I know how often the parents should be bringing provisions to the nest. These birds were clearly struggling, making very few visits to feed their chicks, and I wanted to give them a helping hand.”
When the nestlings were a little larger, David provided a feeder with live mealworms near the box, a source of food quickly seized upon by the parents to provide for their hungry brood. The camera-box had space for a small video camera, which allowed David to spend several hours a day watching a live feed of the activity inside from a discreet distance. The scene was lit by a lamp inside the box, rather than a flash, to ensure the inhabitants were not disturbed, and the main camera was triggered remotely. These
intimate views of the nest activity revealed that the mealworms were well received, and the parents successfully raised all five chicks to fledging.
Great tits naturally nest in tree holes, filling the base of the cavity with a foundation of moss into which they build the nest cup. Sometimes they can misjudge the size of the space, as in the case of a pair of great tits found nesting in a large barn owl nestbox. The female, which is solely responsible for nest construction, had filled the whole box with an enormous amount of moss, dwarfing the tiny nest cup nestled in the top.
COMFORT ZONE
The cup is lined with soft materials to provide a cushion for the eggs and, later, nestlings. Unlike many other birds – including the closely related blue tits – great tits rarely use feathers for the nest lining, instead favouring animal fur and wool. Their efforts to obtain suitable lining materials were investigated in a study in Treswell Wood in Nottinghamshire, home to a long-running nestbox monitoring project.
Over 10 years, from 2000 to 2010, dispensers of artificial wool-like material, coloured red, white, green or yellow, were hung at various sites throughout the wood, and the resulting technicolour nest linings were recorded during routine nest checks. This study revealed that the birds didn’t appear to have any particular colour preference, but it did show that they travelled surprising distances when gathering nesting material. Birds were found to pass through the territories of several other great tits when visiting dispensers, and one nest was lined with yellow material despite being nearly a kilometre away from the nearest yellow dispenser.
There were no dispensers of nest lining material in David’s patch in Norfolk; his birds used a more natural resource. “I watched great tits visiting the carcass of a roe deer in the wood,” says David. “They would rip out chunks of the fur to line their nests, and, as the carcass decayed, they would even go right inside – I think they were feeding on the maggots.” This rather grisly behaviour should not come as a surprise, as great tits are famously adaptable foragers ( see
box, opposite) and have been shown to be one of the most innovative birds in the world at exploiting new food sources.
SMART THINKING
Great tits mainly feed on insects, as well as seeds and fruit in winter, but can turn their beaks to almost anything. They have even been observed using tools in the wild, extracting insect larvae from holes in wood with a conifer needle, and can pull up food suspended on a string. Blue and great tits learned to open milk bottle tops on doorsteps to drink the cream, a habit that started in the early 20th century and continued until the decline of foil-topped milk deliveries. This behaviour quickly spread through the population, in an example of what appears to be cultural learning.
Ornithologists at Oxford University investigated this transmission of information in a fascinating experiment, in which great tits were taken from the wild and taught to solve a puzzle to access food, pushing on either the red or blue side of a door to dispense a mealworm. The birds were released back into different local populations, accompanied by the puzzle boxes. The wild birds quickly learned from the trained birds how to open the doors – either pushing the red or blue side, depending on which trained bird they learned from, and then passing this technique on to others.
Despite this ability to exploit a wide range of food sources, during the breeding season only one kind of food matters: caterpillars. Moth caterpillars are abundant in deciduous woodland during their spring peak, and great tit nestlings rely on this source of nutrition to fuel their development. As with most birds, this growth is swift; the chicks hatch from tiny eggs as naked and blind pink scraps, but fewer than three weeks later they will leave the nest as fully grown birds. The amount of high-quality food needed to fuel this transformation is staggering, and it’s been calculated that the adults will deliver 10,000 caterpillars to the nest during this two-week period.
CHICKS HATCH AS NAKED AND BLIND PINK SCRAPS, BUT LESS THAN THREE WEEKS LATER THEY WILL LEAVE THE NEST FULLY GROWN.
The problem with caterpillars, however, is that they are not around for long. Their job is to hatch, eat, grow and then develop into their adult form, and all this is timed to coincide with the first spring burst of new leaves, upon which they feed. Great tits therefore need to fit into a delicately timed system. If the weather turns cold, caterpillars won’t grow as fast, and won’t be big enough to be a good food source. The timing of the caterpillar peak can be very different from year to year, and what’s amazing about great tits is that they can be flexible in their behaviour in order to match this peak.
BOLD OR SHY?
Ella Cole, a research fellow at Oxford University, is working on the woodland populations of great tits that featured in the puzzle box experiments. She says: “They will choose the time to lay their eggs depending on the stage of leaf development of the trees around their nest site, and if there’s a cold snap once they have already laid their eggs, they will take breaks from incubation in order to delay hatching.”
This behavioural flexibility is crucial to allow great tits to take advantage of the movable feast of moth caterpillars, but they don’t just respond to external cues. Another strand of the Oxford research is investigating the innate ‘personalities’ of great tits – specifically, whether they are ‘bold’ or ‘shy’. Birds are tested in captivity to see how they respond to new environments, and it’s clear that individuals have set, permanent character traits. They may be quick to explore and investigate, following a high-risk, winner-takes-all approach, or more cautious, preferring to ‘live to fight another day’.
The findings from the research suggest that one approach isn’t fundamentally better than the other. What works best will vary from one situation to another, or one year to another, depending on the conditions, so both personality types survive in the population. ‘Bold’ female great tits were more likely to return quickly to their nestbox when a ‘suspicious’ object – a small flag – was placed on top of the box. This clearly demonstrates the risks of over-reacting to a perceived threat, versus under-reacting to a real threat.
One of the benefits of this kind of detailed, long-term study is learning exactly how individuals are related to each other. Some of these findings may come as a surprise to casual observers of the domestic bliss of nesting birds – particularly the fact that around 10 per cent of great tit chicks are fathered by a male other than their mother’s partner. Different personalities come into play here: it appears ‘bold’ males are more likely to look for opportunities to mate with other
‘BOLD’ FEMALE GREAT TITS WERE MORE LIKELY TO FUTURE SUCCESS WILL RETURN TO THEIR NESTBOX DEPEND ON ACHIEVING WHEN A ‘SUSPICIOUS’ OBJECT GOODWILL ACROSS A WIDER WAS PLACED ON TOP OF THE BOX. SWATHE OF THE LANDSCAPE.
females, while ‘shy’ males are more likely to stay with their own mate during her fertile egg-laying period. This ensures she can’t mate with other males, and therefore ‘shy’ males tend to father more of the chicks in their own nest. Overall, this averages out, with both bold and shy males having roughly the same level of reproductive success.
Identifying individual birds also reveals high ‘divorce rates’. Sometimes one member of a pair will die over the winter, but even if both survive they won’t necessarily pair up again. In up to 50 per cent of cases they will take a new mate. Experienced breeders are more likely to stay together, while birds with a chance of getting a better deal will move on.
EVICTIONS AND TAKE-OVERS
Getting to know these birds intimately reveals other sides to their nature. Nestboxes are extremely valuable resources, and the larger, more aggressive great tits have no qualms about violently taking over boxes from smaller blue and coal tits. “We find cases where a nest started by blue tits has been taken over by great tits,” says Cole. “Normally we can’t tell exactly how this has happened, but sometimes we find evidence that the original occupant has been killed.” In one case, Cole and her colleagues found one female great tit sitting on a nest of eggs, and next to her was a female blue tit, her head crushed, woven into the nest lining.
A side effect of these forcible evictions are ‘nest takeovers’, where great tits move in after a clutch has already been started, and add their own eggs to the existing nest. In these cases, the blue tit chicks hatch and are raised along with the great tits, and the end result is a number of rather confused young blue tits that don’t know, at least for a while, what species they are meant to be.
Many of us don’t give the great tits in our gardens a second glance. So it’s worth taking the time to really appreciatetheir beauty, and to remember that the secret lives of these charming, carefree visitors to our bird tables are full of drama, struggle, problem-solving, death and intrigue.