With autumn in full swing and the second wave of migration well underway, changes are visible as the final marked lapwings leave the Czech Republic. Remarkably, some lapwings previously settled in France have also return to migratory mode. For example, Kikina and Prskavka have already made it to Spain, hovering around the Portuguese border. Meanwhile, Nerea and Lulu have been spotted together in a field near Le Mans, France. Although they likely aren’t aware of each other, based on the radio data, it’s an interesting coincidence worth noting.
In contrast, woodcocks have remained silent (last signal received on October 2 from Turbo). This isn't surprising based on past observations. We know from experience that we’ll hear from them again when they exchange their forested surroundings for the sunny Mediterranean. Sometimes we receive updates around Christmas or during their return from wintering grounds. Fingers crossed we’ll hear from them sooner this year!
While we will have to wait a while for the woodcock, as well as for the completion of the second wave of lapwing migration and their final distribution around the wintering area. There are some highlights that we would like to share with you, but it will be good to let them mature for a while. Therefore, we have a bit of a free time in studying the current events brought by the mobile signal from the tags, so this time we will focus our blog on a phenomenon that is completely non-autumn, an activity in the life of lapwings that is exclusively spring, namely egg incubation. However, it is a topic for which we don't have to rely solely on data from our radio-tagged lapwings. Indeed, we have been studying the incubation behaviour of plovers for many years.
Although lapwings can be observed in our fields sometimes as early as the end of January and the beginning of February in recent warm years, they usually start nesting in early April. In some years, new clutches may appear until mid-June. 1 During this time, some females may of course lay more clutches, but these are usually replacement clutches, resulting from the loss of a previous clutch or small chicks. Since incubation of eggs lasts approximately 27 days in the lapwing, there is room for more attempts during the relatively long Czech spring. Sometimes they renest in the same location, but often they will move several kilometres. In the nesting trials of the females monitored this year, the females nested in the same location in three cases, while in seven cases they moved 2-42 km. A curiosity in this respect was Drahuš, who probably needed to clear her head a bit after losing her second nest at Třesovice. Before her next nesting attempt at Světí, less than seven kilometres away, she made a ten-day trip to Austria and Slovakia, during which she flew nearly 500 km!
But let us now concentrate more on the actual care of the chick's parents for the eggs. These are warmed by either parent about 87% of the time. 2 Most of the incubation care is done by the females, who on average are responsible for more than 80% of the entire incubation portion. However, the degree of parental care tends to be highly variable among fathers! While some share parental duties with the female quite equally, we did not see others on the nest at all during several days of camera-recorded incubation. On the one hand, it's not surprising when a third of the male lapwings have two females and now and some manage even more! 3 On the other hand, it should be mentioned (before we start blaming everything on those polygamous guys) that some polygamous males manage to incubate more on all their females’ nests than other monogamous ones on a single nest. 4
However, one of the things our research has shown is that the female has to negotiate the care of the nest properly with the male. 5 In fact, camera footage of incubation often clearly shows the female calling loudly before leaving the nest, and several cues clearly indicate that she is calling to the male. For example, the probability that a male will come to exchange the female increases about fourfold after such a call. This may explain another important feature of lapwing family habits, namely that the male's involvement in incubation is almost exclusively a matter of daytime. Nocturnal incubation is usually left entirely to the female, even by the most incubating fathers. We assume that this is due to the female's fear of calling the male at night. This is because the vast majority of nest predation takes place at night, and the movement of predators around the nest can pose a danger even to the incubating adult if it is inattentive. This is supported by the fact that on the rare occasions when a female has dared to call for a change during the night, the male has often came and exchanged her on the nest. 5
The importance of the male's help in incubating the nest is not only reflected in the increased quality of care for the offspring (nests with more incubating males tend to incubate more 2). In fact, further research has shown that it also has a significant effect on the comfort that the female can afford during incubation 6. In the first place, a female who can rely on more significant male involvement in incubation logically has more time away from the nest and can spend it not only foraging for food but also, for example, by preening her plumage. This has the advantage, among other things, that conspicuous movements during feather preening do not attract the attention of potential predators during incubation and thus do not draw their attention to the nest. Therefore, we were not so surprised to find that females with more male support spent less time tending to their plumage while sitting on the eggs. It was a surprise, however, when we focused on how much the female slept during incubation. It turns out that females who get a lot of help from males with incubation sleep more on the nest. So the poor female "self-incubators" probably almost don't sleep at all during the nest care period. In fact, they cannot be expected to sleep on those rare occasions when they do leave the nest for a while. Why, then, are females with more male support able to sleep more than those who do not have as much male help with incubation? We don't know, but we assume that responsibly incubating males will be highly responsible also in other aspects of nest care, specifically guarding the nest from potential predators. Thus, the female may have more confidence that a responsible male will alert her in her sleep if the nest is in danger.
And how did we find all this out? Over the years, we have used and developed a variety of different technologies and methods to study nest behaviour. Starting with miniature cameras placed near the nest, to temperature and humidity sensors that allow detection of egg heating when compared to ambient temperature, to the sensing of RFID transponders placed in the flag on the lapwing’s leg by a coil around the nest. So, actually, sort of like the entry registration system at the incubation workplace (incidentally, the same technology is used by many of us to get to the house, the workplace, or to prove in the cafeteria that we ordered food on time).
And in fact, the radios we use to monitor the lapwings now allow us to monitor the incubation as well. And not only thanks to GPS, which, due to the high frequency of recordings, allows us to precisely specify the position of the nest. But the transmitter also records activity, using an accelerometer. And it is this sensor that allows us to detect the incubation behaviour of the monitored lapwings very accurately. If a lapwing is incubating, it will show up beautifully in its activity - by clearly showing regularly alternating periods of high and low activity during the day and virtually no activity during the night (see Figure 1).
Figure 1: A day of incubating Belinda. In the left part we can see the movement of the female around the nest site and surrounding fields during the incubation breaks, but also the highest concentration of points indicating the presence of a nest. In the right part we can see the alternation of high activity (incubation breaks - we can see that Belinda clearly had a lucky hand in choosing the male!) and low activity - incubation of the nest. Then at night we see, with a few exceptions, a continuous presence on the nest.
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