This latest post has been written by Mo Verhoeven, RSPB Senior Research Assistant, as part of Project Godwit, and was first published on the Back from the Brink website.
On January 14th this year, Jelle Loonstra and I handed in our joint PhD on “The behaviour and ecology of the Black-tailed Godwit”. The next day, I was on an airplane to Chile with the mission of outfitting Hudsonian Godwits with transmitters to record their 14.000+ km migration from Chile to the North American Arctic. I was coming from winter, which was clear from my pale skin and a permanently smoky smell imparted by my woodstove. But suddenly I was in Chile, wearing shorts and freed from my PhD for the first time in months. A good start to 2020!
Blog author, Mo Verhoeven (taken by Rob Buiter)
A few weeks later (at which point I happened to be in the forests of Maine, wearing smoky snowpants), I received a job offer to work for the RSPB as a Senior Research Assistant on Project Godwit to monitor the Godwits nesting at the Nene Washes. I imagined the tumbling Lapwing, the whirring Snipe and the nesting Godwits. It was hard to say no.
On March 15th I arrived in the UK. It was sunny, the Washes were partly flooded and the first Godwits had returned! The stage was set for a beautiful spring. And a beautiful spring it was, with flowers blooming, nests being built, and chicks to come…but on the 23rd a nation-wide lockdown was announced and all fieldwork was cancelled! What to do?
Black tailed godwit (c) RSPB Images
Project Godwit had already collected data on breeding Godwits at the Nene Washes in 2015-2019, which meant I could start analysing some of that. First, I analysed data from the eight geolocators that had been retrieved in previous years. Geolocators are data-loggers that continuously log the ambient light-level.
Each geolocator is attached to a ring that is placed on a godwit’s leg. The Godwit then carries this geolocator with it throughout the year – on migration to the non-breeding grounds and back to the Washes again in the spring. Researchers then do their best to capture that same bird again; if they’re successful, they remove the logger and use the stored light-level data to establish the moment of sunrise, midday and sunset throughout the year.
When you know the length of each day, you can estimate the latitude (north/south), since this varies predictably with date across the world. Estimating longitude (east/west) comes next and this relies on a centuries-old technique. First you log the moment of midday at a specific location, usually Greenwich. From this you can calculate the shift in the time of midday relative to Greenwich, and therefore determine how much the godwit has moved to the west or east relative to Greenwich. This is why seafarers had chronometers and why precise chronometers were worth a lot of money.
Raw light-level data recorded on the geolocator carried by OB-OL(E)
Two of the geolocators I examined had logged especially interesting migrations (during my PhD, I analysed more than 300 migrations by Dutch godwits – these two were immediately distinguishable from the pack!). The first was from ‘Cornelia’, a head-started chick released at the Nene Washes in 2018 (also learn more here).
Black-tailed godwit chicks are being head-started to boost the number of Godwit chicks that survive to fledging age. Chicks are reared by our project partner the Wildfowl & Wetlands Trust (WWT) at Welney Wetland Centre and released once fledged. The nearly fledged chicks are fitted with a unique combination of colour-rings and some are also fitted with a geolocator. Cornelia was released on June 27th 2018. She left the UK on the evening of August 13th and arrived in Africa on the night of August 15th, having probably flown non-stop.
The other was from a male Godwit known as OB-OL(E). In 2018, this male left the UK on June 21st, went to the Balearic coast of mainland Spain, and stayed there for three months. That’s not very uncommon. But on October 2nd, he crossed the Sahara and went to the Inner-Niger Delta in Mali. This is very late in the season for such a flight – in fact, it’s the latest southward Sahara crossing on record for an adult Godwit! For context: some Godwits start migrating in the opposite direction, from west Africa back north, as early as the second week of September. Why do Godwits behave so differently, and how do these individual differences come about? Interesting questions that challenge current knowledge!
Map of the migration route of godwit ‘OB-OL(E)’
The other analysis I have worked on during lockdown is comparing adult, nest and chick survival rates between an earlier period of research at the Nene Washes, during which the Godwit population at the Nene Washes increased (1999-2003) and a more contemporary period (2015-2016) in which the population has declined. This work shows that nest and chick survival, but not adult survival, are low in the contemporary period compared to the early period.
The recent decline at the Nene Washes is therefore likely the result of lower reproductive success resulting in fewer birds recruiting at the Nene Washes. This study also indicated that nest survival was lowered because of an increase in nest predation. The reserve managers had already been thinking this was the case, and in 2017 started using special gates and electric fences to keep mammalian predators from depredating Godwit nests. My next task will be to evaluate whether and how effective those efforts were. I’ll keep you posted!
Project Godwit is a partnership between RSPB and WWT with major funding from the EU LIFE Nature Programme, the HSBC 150th Anniversary Fund, Natural England, the National Lottery Heritage Fund through the Back from the Brink Programme, Leica and the Montague-Panton Animal Welfare Trust.
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