Unravelling the mystery of Shining (bronze) cuckoos' dark green eggs

This week we've had a paper published in Auk which marks a personal triumph!

In 2010, I travelled to Kaikoura, New Zealand, to do some pilot work as a Phyllis & Eileen Gibbs' Travelling Research Fellow (a one-year fellowship from Newnham College, Cambridge).  With the support of Rebecca Kilner  (U. Cambridge U.K.) and Jim Briskie (U. Canterbury NZ), I investigated whether the study population of Grey warblers (a.k.a. Grey gerygones) and Shining cuckoos (Chalcites lucidus a.k.a. Chrysococcyx lucidus... phew!) could help us to unravel why Shining cuckoo eggs are dark olive-green and to learn more about their chicks.  

Most species of cuckoos in the Chalcites genus lay dark green eggs, while their hosts lay eggs that appear very different.  Back in the 1980s, Marchant and the Brookers suggested that this might be to help hosts detect cuckoo eggs, or perhaps, to avoid other cuckoos from removing their eggs preferentially.  It wasn't until 2009 however, before Naomi Langmore and colleagues produced a nice comparative study using animal vision models which started to investigate these hypotheses. 

With the help of Justin Rasmussen, who was conducting experiments for his PhD on the cuckoos, I decided to test this hypothesis with an experiment: if cuckoo eggs are visible for hosts, do they show rejection behaviour?  Justin and I added a clay egg that was a similar hue to Shining cuckoo eggs (according to calculations from an avian vision model) to as many Grey warbler nests as possible. However, these varied in brightness - same as cuckoo eggs, twice as bright, or white (the maximum brightness possible).  Despite being highly visible, none of our hosts showed any sign of rejecting the eggs, and instead incubated them along with their own eggs.

Much to our surprise, however, four of the nests were parasitised naturally by cuckoos after we'd acted as cuckoos ourselves.  And, at three of these nests, our "cuckoo eggs" were taken instead of a host egg!  

A Grey warbler (Gerygone igata, Grey gerygone) nest after predation - see the hole in the roof.

Frustratingly, many of our host nests were eaten before or during our experiments - one peril of trying to conduct experiments with New Zealand birds at unprotected sites on the mainland!  New Zealand birds just aren't adapted to coping with the hunting strategies of rats, stoats, weasels, possums, and cats that have been introduced (intentionally or otherwise) by humans.  Despite our best efforts, this kept our sample sizes smaller than we would have liked.

Luckily for us, four years later Ros Gloag, Naomi Langmore and others conducted a similar experiment with the closely related Little bronze cuckoo and its Gerygone host in Cairns, Australia.  With a great sample size, they showed that cuckoos do indeed appear to remove foreign eggs preferentially over host eggs, and at far greater rates than hosts.  The publication of this paper gave our results greater weight, because the two studies produced similar results.

So, six years later almost to the day, our efforts have finally paid off!  I also learned a valuable lesson - without pest control or physical protection, we are unlikely to learn much more about cuckoos and gerygones in New Zealand. Grey warblers inhabit scrubby edge habitats.  Unfortunately, Grey warbler habitats are rarely the types of forest chosen to be protected in conservation projects. The future might lie in finding as many nests as possible across the country. This will only be possible with citizen science projects like this one started by Michael Anderson (Massey University NZ).  

Do mothers bias offspring sex ratios in carotenoid-rich environments?

2nd hihi paper for 2016 out @ Behavioral Ecology!

Kirsty J. MacLeod, Patricia Brekke, Wenfei Tong, John G. Ewen, Rose Thorogood

Behavioral Ecology (2016) 28 (1): 131-137.

Here we've proved that non-significant results can be published!  As part of a wider supplementation experiment investigating the effects of carotenoids (a dietary biochemical responsible for birds' pigmentation and implicated in their immune systems) on hihi, we determined the sex of as many eggs laid as possible.  By following these nests closely in the field, (including hunting tirelessly for dead nestlings thrown from the nest by tidy parents!) we managed to collect a dataset to test whether mothers invest more in sons when these are likely to become sexier adults relative to daughters.  There is some evidence that hihi males with greater access to carotenoids when young achieve greater reproductive success in adulthood (see nice work by Leila Walker during her PhD here and here).  Therefore, we surmised that mothers better able to provision sons with carotenoids might invest in producing more of them to improve their fitness.  Data from two field seasons however failed to find any evidence for this, and provides more evidence that sex-ratio manipulation by mothers is difficult to detect.

Read more about this paper, and Kirsty's companion paper on how mothers manipulate hatching asynchrony, in this nice blog post on her site.

Informed birds visiting Antzz in Helsinki

Although our work focusses mainly on birds, and the consequences of their information use for others, some of the best examples of how social behaviour evolves are to be found in invertebrates.  From August, I'll be a long-term visitor to the ANTZZ team at the University of Helsinki, led by Prof. Liselotte Sundström.  Lotta is one of the directors of the Centre of Excellence for Biological Interactions (our collaborator Prof Johanna Mappes, in Jyväskylä, is another), and being here offers a really exciting opportunity to learn more about social evolution from the view point of Formica ants.  Vix and Liisa will be visiting regularly from Cambridge, and I'll be visiting them often too. 

See here for more about Team ANTZZ

Join us for ISBE bingo!

We've been inspired by Bree Rosenbaum's excellent Graduate Student Bingo for Evolution 2016 - and with her gracious permission, we've copied and pasted, and come up with some new challenges (to avoid a complete Melania Trump-ing), and now have an ISBE-specific version.  

Read instructions and download bingo card here

Then come along and join us at ISBE in Exeter (28 July - 2 August, 2016).

Enjoy!

Kirsty's first hihi paper accepted in Animal Behaviour!

Great work Kirsty - her first hihi paper has just been accepted for publication in Animal Behaviour.  

Kirsty took advantage of data collected in the field over ten years ago, and combined this with our long-term breeding records for the Tiritiri Matangi population. Some hihi can live for around 10 years so this was perfectly timed!

Science Cafe kicks off 2016 Cambridge Science Festival

Kirsty and Rose are running the Science Cafe event again as part of this year's Science Festival.  Despite pretty awful weather conditions on Saturday March 5th (gales, rain, and hail!) we reached over 70 people during the 3-hr event in the Cambridge Market Square.  Our goal is to communicate how exciting science is to an audience who perhaps wouldn't normally come to the Science Festival - fingers crossed for better weather next weekend! 

Latest research: how hosts assess parasitism risk

The outcome of two years of field experiments has been published today in Scientific Reports.  Our previous work has shown that reed warblers are much less likely to reject an odd egg from their nest than they were in the past, and that this correlates well with the local risk of parasitism.  But, how do they assess this risk?  

The decision to remove an egg is not without its own risks - hosts may remove the wrong egg, or break their own by mistake.  Close surveillance of their nests to attack a laying cuckoo is also risky because of the cuckoo's similarity to a hawk - attacking a 'cuckoo' could end up being a deadly mistake.  

Here we show that reed warblers only reject an egg when they can combine information gathered from seeing a cuckoo at their nest, with that gained by observing their neighbours mobbing a cuckoo next door.  In other words, neither social nor personal information is sufficient - instead a wide source of information is required.

See the press release here

(Image by Richard Nicoll www.richardnicollphotography.co.uk)

Liisa Hämäläinen begins her 1st field season

Liisa is now spending her time out in Madingley Woods, collecting data to compile a social network for the blue and great tits.  Her first experiments will combine captive experiments with specific birds that she'll be removing (temporarily!) from the woods.  It will be a busy few months, good luck Liisa!

Good luck for the field season on #Tiritirimatangi @VixFranks

Victoria is on her way to New Zealand for her second field season.  She'll be based at Tiritiri Matangi Island until April 2016, and manipulating the ways that juveniles learn about their environment.  If you're visiting New Zealand, make sure you include a trip to Tiritiri to visit Vix and our hihi!

Congratulations @VixFranks on a job well done!

Vix is now officially a PhD student after flying through her 1st year viva today.