Snowy Plover females have a very peculiar behaviour: they frequently desert their broods leaving back their young chicks. Their male partner then has to deal with the offspring alone, an example from nature for a modern single parent family. After abandoning their broods, Snowy Plover females quickly re-mate and start a new breeding attempt with a new partner. This can happen in the same breeding area or the females can travel up to 1000 km and try their luck elsewhere, which has also ramifications for the genetics of the species.

This unusual emancipation enables the plover female to have a lot more chicks than when staying with the brood and caring for the young. Deserting the brood though is a delicate balancing act as the abandoned chicks receive less parental care and as a consequence may not survive as well as if the female would have stayed around. Fortunately, plover chicks are nidifugous meaning that they can already run and search for their own food within a few hours after hatching from the egg. The parents are mainly required to brood the chicks when it’s cold, warn them from predators and protect their offspring from rival plover families. Yet, a few years back we observed at our site that in families, in which the female deserted, the chicks did not survive so well as in families where the mother stayed around to care. Could this strange behaviour perhaps explain why Snowy Plovers are threatened and their numbers are going down in many places? Are the females doing something that may have been good in the past but is now rather hurting their own reproductive success.

Kriszti Kupán decided to look at the dynamics of female desertion in more detail. She re-analysed the previously published data, where we had established that single parent families have reduced chick survival. She used our well curated data on Snowy Plover brood care and chick survival for the years 2006 until 2012, published as part of the CeutaOPEN data base. To make this happen, Kriszti showed incredible dedication and persistence: she started the analysis in 2015 during her maternity leave and from late 2017 she continued this part-time whilst raising her (full disclosure here: ‘her’=’our’) own three kids. You can imagine that we are really happy that the study got finally published in the journal Behavioral Ecology this week and it also received some nice media attention.

So what do we describe in this paper? Kriszti, first found that the length of female care in Snowy Plovers is, as in other plovers, related to seasonality and brood size. Early in the breeding season almost all females desert their broods shortly after hatching. Later in the season, they stay longer and a few stay then even until the chicks are independent. This makes sense: early in the season, chick survival is very high and females have lots of remating opportunities because there is still enough time to finish a new breeding attempt successfully. Also, in our population there are almost always lonely males available as for every adult female there are about two adult males. She also found that females would stay longer when their broods were larger whereas when there was one chick only, they quickly left the brood. Snowy Plover clutches contain most of the time three eggs but we had previously experimentally reduced and enlarged broods, which came in handy here. Also, in nature occasionally chick adoption occurs. She also found that the present brood size, the brood size on a given day was a very good predictor whether a female would continue to care or not. Previously, researchers had mainly looked at the initial brood size. Yet, if the initial brood size would be so important for females when deciding how long to care, they would have little flexibility and ride out their decision to care all the way through the end.

This was clearly not the case. Instead, Kriszti found that when the brood size would drop because a chick died, the female often deserted shortly after. This resulted in a very strong temporal relationship between chick death and female desertion. Right before or after a chick died, the female was much more likely to desert than when all chicks would survive. To us this shows that Snowy Plover females are incredibly sensitive to the condition of the chicks and they flexibly adjust their parental care accordingly. But there is more to it: there was a strong seasonal pattern for this association. Early in the season, when conditions were good enough for one parent to raise the brood successfully alone, females always deserted. We assume that most of these females re-mated quickly, for a bunch  of them we actually were able to confirm this as they stayed at our site. Conversely, late in the season when there was not enough time to have another successful breeding attempt, the female would stay with the family. In the middle of the season, the females committed themselves first to care but when things with their brood seemed to go South and chicks started to die, they abandoned the sinking ship and looked for new mating opportunities. Because there are many more males than females in our population, the males don’t have the re-mating option. A deserting male would struggle to find a new mate and so they are better off caring for the chicks alone no matter what.

It seems after all that the Snowy Plover females are doing the very sensible thing: they leave the brood when they are not needed because the chicks survive anyway or the chicks die despite the female caring for them. Hence the deserting females are certainly not to blame for the decline of Snowy Plover populations.       

Snowy Plover chicks are adorable fluffy little critters. At least for us – we enjoy watching them bumble around at our study site. For others, these flufflings are more than food for the eyes, quite literally, perhaps the next snack – a few welcome extra calories that can become crucial in their daily struggle for survival. As the chicks can’t fly yet and most predators will outrun them, especially when they are young, they rely on camouflage to avoid detection by their foes.

What adaptations have chicks evolved to stand a chance in this game of hide and seek? This is a question of life and death and provides these tiny Snowy Plover chicks with an extraordinary challenge as they live on the salt flats where there are little places to hide. It’s no rocket science to assume that their feathers will provide some protection. The chicks’ mottled plumage, which features many colours of the soil, helps them to blend into the background. Yet, right now we actually only presume that this is the case - there is a dearth of studies on camouflage of chick plumage; not only for Snowy Plovers but pretty much for all precocial chicks.

The colours are not the only way how the chicks can use their feathers to evade predators. When you look closer at a plover chick, you will notice that there are tiny feathers sticking out from the chick in regular irregularity. This is a common theme for almost all chicks of shorebirds and other precocial birds. A very cool example for this is represented by Golden Plover chicks, which might be easily mistaken for a moss. Appendages are not restricted to birds alone, strange skin elements that stick out of the body are actually a common theme of a number of prey species. Prominent examples come from frogs, cuttle fish and of course, hairy caterpillars. Often these appendages have been heavily implicated in serving masquerade, another important camouflage mechanism where animals imitate in an inedible object. Yet, we wondered whether the tiny feathers actually help the small chicks to hide, and in particular, they serve to conceal the chicks outline when there is no place to hide.

Vroni Rohr took the lead for this study and investigated whether and how appendages such as neoptile chick feathers reduce detectability for her master thesis. She first tested the principle with an artificial object: a simple circular shape on a plain monochrome background to which she added ‘appendages, simple lines sticking out with varying density. In this process Vroni created a lot of digital images and measured contrast and luminance of the area surrounding the circular object with appropriate image analysis software. The first results were promising. She found that the appendages indeed reduced the contrast between the outline and the background and led to a transition zone of luminance. Both results were in the predicted direction suggesting that the appendages helped to make the outline of the object harder to detect. Over the course of her digital experiment, Vroni then varied various parameters of appendages and background to capture some real-world characteristics of feathers, habitat and also predator visual system. She found that the appendages actually had the largest effect when accounting for spatial acuity, a key property of the visual system of the predators. Spatial acuity is the ability to resolve two points in space, the higher it is the better the eye sight. Mammalian predators that are commonly eating plover eggs and chicks have a rather low acuity and here the results suggest that appendages made the biggest difference and helped to conceal the outline of the object the most.

In a second step, Vroni then took images from real Snowy Plover chicks in their natural hiding places, cropped them and then put them back at exactly the same place on a second picture that we had taken from the empty background and included the chosen hiding spot of the chick. However, before doing so, she digitally shaved off the tiny feathers in the treatment group whereas she transferred the chicks with their protruding feathers in the other group. These feathers were protruding only for a few millimeters from the chick and Vroni then compared contrast and luminance of the region around the chicks. Amazingly, the shaving treatment actually had an effect. Without the feathers sticking out, the outline of the chick had a higher contrast to the background suggesting that the shaved chicks would be more likely found. The shaving, however, made no difference for the luminance in the transition zone, so the concealment is more likely to work through reducing outline contrast.

Based on these results, we argue that this function of the chick feathers has so far been overlooked. The study was recently published in Scientific Reports. Now, whilst we are excited about these findings, it is important to put things into perspective and not get carried away too far. The better outline concealment alone will not be enough for the chick to escape the predators’ notice. There is no doubt that the main protection is most likely coming from the cryptic plumage colouration. (Interestingly, the camouflage of cryptic eggs has been studied alot more in detail already probably because it is an immense effort to locate precocial chicks and keep them still for the picture, as we learnt during our study.) Also, mammalian predators most likely rely on their noses to find the chicks although their eye sight might be important. Still every little helps in the race of survival and the protruding feathers contribute their little bit. We also noted that the juvenile shorebirds (and other baby birds!) keep these protruding feathers pretty much until the age when they can fly giving more credibility to our hypothesis that this is an adaptation to avoid detection by ground predators.

Clearly, chick camouflage deserves a lot more attention and future studies.   

We did it. We have made 11 years (2006 to 2016) of Snowy Plover data freely available here. The data are described in a publication in Scientific Data. Observations of 1,647 individually marked Snowy Plovers. Monitoring of 794 nests and tracking of 415 broods. Pretty powerful stuff when you are bird- or data-enthusiast. Putting this together was a huge effort lead by Luke Eberhart-Phillips – it took him the best part of a year to get everything into shape.

 This is a big step for us, so I want to briefly outline why we did this and what the ramifications are. The main motivation for our work is understanding our beloved plovers better. Ultimately, we want to figure out why females desert their broods and mate with other males whereas their first males are left to look after the chicks alone. We also want to improve their conservation, which means we need to figure out why chick survival at our site is so poor and what management actions are necessary to improve this. All this requires a lot of detailed field observations and hence a lot of work to collect and curate the database. Over the years we have invested thousands of hours into this data collection. This is not only our own work, but also countless hours committed by students and volunteers who have been part of the journey. There is more to it than the nearly 20,000 observation hours. First, our fieldwork required a lot of preparation: chasing funding, preparing permit applications, getting the equipment and the team ready and so on. This is followed by three months of fun chasing and watching wild animals, and, of course, enjoying Mexico. Fieldwork is why we are biologists in the end. Once the fieldwork is done, a lot of more work is needed: the data have to be entered and curated – meaning many revisions of the database. We then use some of the data for our own research purposes, but since we are only a small team, there is only so much that we manage to analyse.

 Sitting on so much data after so many years is somewhat frustrating because there are countless projects that we simply do not have time to do. So, we have thought long and hard about how to change this limitation. Eventually we determined that the way forward is to get you involved – with no strings attached. I admit it is occasionally scary: we feel somewhat naked and vulnerable at the thought of having our science scrutinized even further. However, we are confident that this is the right decision and excited about where this will lead us in the future. We realize that there are lots of ways to analyse and wrangle the database, and hence other users may produce slightly different results from us. Perhaps in a few years we have another brilliant idea for a high-profile science project, yet somebody may have then done it already thanks to our data. But ultimately, we decided that the benefits will outweigh the costs. We are confident that we are doing robust science, but like any long-term field project, there will be the occasional mistake in the data base that despite our best efforts we have overlooked. These mistakes will be corrected in future updates of the data base, while keeping tidy version control in the database’s GitHub repository. We hope that future users will utilize CeutaOPEN to address cool questions about ‘our’ Snowy Plovers that will stimulate new research projects that we would have otherwise have never thought of. Certainly, getting more people interested in our plovers and getting more and better science done will only benefit the birds.  

 Publishing these data was also meant to reward the people who were involved in their collection. Many field assistants, collaborators, and students who helped with permitting and worked for more than a year with us have become authors on the data descriptor. We have been incredibly lucky with them: without them we could not have done this. Most field assistants worked as volunteers very long hours under challenging conditions. They put in a lot of enthusiasm and effort and were in for research or training – but never for the money. (In science there is not a lot of money, especially when you work for your degree.) The field assistants can now see that the data they have collected are part of a big study and hopefully will be used for a long time. They can be proud of their contribution!

 So far, we also have been in the fortunate situation to have had always financial support to cover most of our basic costs. Without those public and private organizations (listed here) the data collection would not have been possible for so many years. Government agencies have trusted us and permitted us to conduct our studies for the best of the birds and the people. With all this trust comes responsibility and hence we want to make sure that we make the best use of the resources given to us. Making the database freely available means that our past, present and prospective funders can see for themselves how we have spent their contribution to our work.

 One important consideration in deciding to make the data publicly available is also an awareness that academic life is dynamic and constantly changing. Today’s science is often a huge collaborative effort. Academic life does provide a lot of freedom but most people, including ourselves, are on temporary contracts with high employment uncertainty. Furthermore, life and research careers evolve. Sometimes, professional relationships turn sour and there is a high potential for conflict about the data use. This brings up a lot of questions: Who owns the data from a long-term collaboration? Can someone actually ‘own’ data collected from wild animals? There are a lot of stake-holders with a claim on the data. 1) The students who spent countless hours in the field to collect them. 2) the supervisors who provided guidance and resources. 3) The universities/funders who provided the money to do the research. 4) The countries and local communities where the research has been conducted. Disagreements among stakeholders about data usage could mean that the data become locked up until conflicts are resolved. We don’t have the answer to the complex issue of data ownership, but by making the data open-access we aim to ensure that they are not lost and that their potential use is maximized.

 Finally, we want to inspire others to conduct similar studies and share their own data. It has been a lot of work to collect these data, and it feels as if we are publishing a big part of our professional lives. But now we are excited to see what will happen next! We hope that this endeavor can kickstart new collaborations and we plan to make more data from subsequent years available after careful curation and after current student projects are finished.

 We invite you to dive into CeutaOPEN. We are convinced that going open access will make our own science better and more transparent – a move that can only benefit conservation of  Snowy Plovers.

Yet, reading through my last blog entries from 2012, it is very fitting to continue with a very basic but important problem: how do breeding plovers deal with the changing tides?  Plovers are habitat specialists that often nest in intertidal habitat. This has many advantages, as in these open areas approaching predators can be spotted early, so that the nesting plovers can leave their nests and stay safe somewhere until the predator is gone. From their safe spot they can then watch how their expertly camouflaged eggs are overlooked by hungry predators - more often than not. But living in intertidal habitats brings up a new set of differently challenges. Probably the biggest one is the periodically changing water levels that shift the shoreline throughout the lunar month. From egg- laying to nesting each Snowy Plover nest will experience 2 to 3 spring tides that could flood the precious nests and kill their eggs. Unlike other salt marsh specialists, plover embryos cannot endure nest flooding that last longer than a few hours. And once the eggs are laid the plovers cannot really change the nest location, so this is an important decision. On the one hand, they need to choose the nesting spot wisely otherwise the nest is flooded. On the other hand, they want to nest close to the water as water means food especially for their chicks once they have hatched. How do they deal then with the risk of nest flooding? I was very lucky to recruit Silvia Plaschke, a bright student from University of Graz, back in 2016 to work with me on this for her Master project. 

The observations of 2012 suggested they should take the flooding risk seriously as back then a lot of nests failed due to flooding. In fact an entire cohort was wiped out in this year, not a single offspring fledged. But then 2012 seemed an exceptional year for our local Snowy Plovers, we had not witnessed such a devastating flooding event in any of the seasons before. A first question then is, how big is the threat of flooding? To investigate this we gathered nest fate and nest initiation patterns from ten breeding seasons and compared the differences between flooded and not flooded nests. First, we found that actually very few nests are flooded by the tides. From about 750 nests monitored, only 6% were flooded over the years. However, we found that in two of the ten seasons nest flooding was actually the second most important reason for nest failures. We also discovered that nest flooding ware much more likely to happen late in the season. Nearly all flooded nests were initiated in the second half of the season. Tropical storms in our population preferably occur at the end of the season. At this time the tides are already getting higher again and the two factors probably contribute to the higher rate of nest flooding then. One wonders, how the climate change will impact the timing of the storms and then how the plovers will deal with this.    

Finally, we found that the timing within a spring tide cycle was important. This required the use of circular statistics to model the periodicity of the spring tide cycle. A simple linear model cannot deal with this variation. I’m glad that our colleague Martin Bulla took over this task. The models showed that nests initiated around neap tides had a 50% higher risk to be flooded than nests initiated around spring tides. From this we concluded that timing of nest initiation was really important. One reason why spring tide nests do better than neap tide nests could be that the plovers experience how far the highest tides during the month reach into the salt flat and can comfortably pick a safe spot. By contrast, Snowy Plovers that initiate their nests during neap tide do not have this information. 

Following this we asked whether Snowy Plovers then do the sensible thing and initiate their nests during spring tide. The answer for this is a confident ‘possibly’. Indeed, we did find that more nests were initiated during spring tides than during neap tide but not overwhelmingly more. Plovers might also take other measures to ensure that the nests are not flooded. For example, they might instead nest on an elevated spot. However, many of these alternative mechanisms have disadvantages because nesting on an elevated spot in an otherwise flat area means also that their nests will be more conspicuous to predators. In our paper we therefore argue that actually adaptive timing could be a cheap mechanism to deal with the risk of tidal flooding effectively.

Strikingly, when one looks at the maximum high tides over the years, the plovers have picked exactly the time when the high tides are the lowest. Of course, only then much of their nesting habitat becomes available but it also helps to reduce the risk of flooding. This seems to be common also in other coastal bird populations from temperate zone but there during the rest of the year the conditions for rearing offspring are not great. In Mexico, I sometimes wondered why the plovers do not simply start earlier as temperatures are warm. Our study suggests that the tides could hold the keys for understanding why plovers breed when they breed at our site too.

The Ceuta Snowy Plovers are back strongly. Actually they were never really gone. Rather they decided to delay their breeding start and have just begun to nest madly because the season has already advanced. Over the last 24 hours we found 11 new nests which means our total nest count for this year is already 17. This is about 70% short of our usual figures around this time. But it looks a lot better than we thought about a week ago. What happened?

The Snowy Plovers moved North. Some are still nesting at the abandoned salt works where all the water is gone. These are the conservatives. They just seem to like the salt works and can’t leave it even if conditions there are catastrophic. About a third of them decided to nest around a tiny puddle of water. We called it Arroyo de Esperanza (Pond of Hope). It dried out on Friday.

I’m afraid all these families will have a hard time. There is no accessible water because between them and the water front is a 500 m stretch of thick mangrove forest. And Snowy Plover families usually don’t pass through mangroves. They could also make it to the beach but again there is mangrove forest between the nests and the beach. In a few weeks we will see what trick they will pull off again.

The other half, the adventurous plovers, decided to leave the salt flats this year and nest around a massive lagoon about 500 m North. This lagoon is slowly drying out and the plovers are quick to put their nests into the dry areas. We found nine nests there alone and haven’t searched the area properly yet. I wouldn’t be surprised if we would find 20 more nests in the lagoon. They are currently nesting in high densities and there are a lot of plovers around. The lagoon breeders look like the winners at the moment. Once the chicks hatch in three weeks the families should be able to find water even if it means that they have to walk a few kilometers because the water will retreat further. At least if there are no drastic changes with tide or weather. But they don’t have a mangrove obstacle to cross.

The problem with the lagoon breeders is that their nests are vulnerable to flooding. Fortunately the monthly high tide has just passed and should only come back once their chicks have hatched in 25 days.  Nevertheless, all we know is that  conditions are volatile, so keep your fingers crossed.

Another promising observation of today was that many of the lagoon breeders seem to be Ceuta chicks that hatched here last year. Of the nine nests at least six have one parent who hatched in the salt flats last year. So the population has not disappeared. We will see whether it pays off to be conservative or adventurous as a plover. I would put my money on the adventurous plovers. But then again, I don’t have any money and the plovers continue to surprise me every year…

Now we have some catching up to do. Nests everywhere want to be marked and the parents are waiting for us to take pictures of them and give them new color bands. Lots of work to do over the next few days.  Good that more help will arrive in a few hours.

Rain, heat, mud and more sand flies. The rain means that the breeding season for Snowy Plovers and the other ground nesting shorebirds and terns is ending now. Last week some heavy down pours flooded the last dry parts of the nesting area. Everything was covered by 10 cm of water. All remaining active Snowy Plover and Least Tern nest were lost and the chicks died in the eggs.

The end of the season is unpredictable for us as well as the plovers. At Bahía de Ceuta the rain season usually starts around already 24 June, but during the first three weeks there are often only showers. Nowadays global climate changes makes predicting the date more difficult even the local shamans struggle to forecast the beginning. Over the last few days many plovers started to gather in flocks or moved to other beaches or other wetlands, a clear sign that breeding is over. We had hoped that at least some more of the Snowy Plover nests would get lucky and hatch because the breeding season this year started very late but it didn’t work out in the end.

Working in a wetland during the rain season is very exhausting. Everything is muddy and slippery, it is hard to move around. Even plain walking requires some effort. The ground is pure, deliciously smelling mud and with every step one sinks ankle deep into it. There are mosquitoes and sand flies everywhere. The repellent does not help anymore because of the high humidity. Even the muddy roads are not safe after rainfall and we have to be careful not to get stuck with the car. Temperatures at night rarely fall below 25°C and without air condition (which does not exist at the field station) it is hard to catch sleep.

We will terminate our intensive fieldwork this weekend. After more than 80 days without a break everybody is tired. The heat, mosquitoes and the long working hours day and night have taken their toll. We love field work but during these days everybody is glad once we can call it a day. At the moment we tie up the loose ends. We have to clean up, prepare the equipment for storage until next season, enter the data into spread sheets and tables. Field work is reduced to the only remaining task: trying to locate and follow the remaining families and identifying the color banded plovers that are still around. A few more chicks will hopefully fledge, so this season will not be regarded as a complete disaster.

We will check the site and the progress of the remaining families once more on one of the next weekends.