Black-tailed Godwits signal drought resistant meadows in the hot summer of 2018

Ruth Howison, Jos Hooijmeijer and Theunis Piersma report:

The Netherlands is home to over 85% of the northwest European breeding population of the continental subspecies of Black-tailed Godwits Limosa limosa limosa (Fig. 1). Black-tailed Godwits are an iconic meadow bird and the national bird species of The Netherlands. The Dutch population originated in the wet grassland meadows created by many generations of Dutch dairy farmers (Beintema 1986). However, due to intensification of agricultural practices (Kentie et al. 2015, Howison et al. 2018), the population has declined by over 75% since the first population size estimates in the 1960s (Kentie et al. 2016)

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Figure 1. A Black-tailed Godwit, individually marked with colour-rings, issuing alarm calls to nearby chicks from an elevated position. (Photo: R.A. Howison).

For the past 15 years, the RUG team ‘Skries’ (most years consisting of ca. 10 paid field technicians and ca. 10 students and international volunteers) has carefully monitored godwit population events (establishment, nest locations, egg and chick production and postbreeding movements) within what is now a 11,400 ha study area in southwest Friesland (municipality Súdwest Fryslân). In addition, the locations of a small number of black-tailed godwits population have been tracked with solar PTT satellite transmitters (Microwave Telemetry, Columbia, MD).

In 2018, Europe experienced one of the hottest summers on record. Extreme temperature anomalys bring with them extreme weather as heat waves, droughts, and floods, which negatively impact agricultural as well as natural systems. For southwest Friesland, air temperatures in early March dipped below average, freezing most of the countryside (Fig. 2). However, soon May and June followed with maximum daily temperatures exceeding the upper limits of the long term average calculated over the past 28 years.

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Figure 2. Daily temperatures (oC) from 1 January until 24 August 2018 plotted against the long-term average ±SD (from 1990 to 2018), obtained from Stavoren, The Netherlands.

Using vegetation indices measured at 16-day intervals by satellite imagery (see Howison et al. 2018 for methods) at the level of fields, we tracked the response of the grassland habitat in the province of Friesland. We compared the situation on 10 May 2018 (Fig. 3a), the moment when grass biomass is high, i.e. just before the widescale mowing, with the situation on 14 August 2018 (Fig. 3b), i.e. when the negative impacts of the drought on the vegetation were most evident. Based on this comparison, we mapped (Fig. 3c) where the impact of drought was light or even absent, i.e. where plant growth increased (Green), where drought had a negative impact, i.e. the vegetation index had decreased (Red), and where vegetation showed little change (Yellow).

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Figure 3. Tracking habitat change with vegetation indices (MODIS EVI) between (a) 10 May 2018, (b) 14 August 2018, (c) Log change ratio between the two dates, where Red indicates a decrease in greenness, Yellow indicates little or no change, and Green indicates an increase, (d) The spatial distribution of Black-tailed Godwits, overlaying the log change ratio, during the postbreeding period 2018 (after 15 June 2018).

We then compared two measures of godwit distribution with this quantitative assessment of the impact of drought on the grassy vegetation. (1) By weekly counts of all godwits in all 3014 fields in our study area, we measured the godwit distribution during territory establishment, egg-laying and early incubation (26 March to 22 April 2018). (2) On the basis of the locations of individually colour-marked birds and godwits tagged with satellite transmitters, we quantified the distribution of postbreeding godwits fuelling up for southward migration from 15 June to 15 August (Fig. 3d).

During territory establishment and early nesting, when their movements are necessarily constrained, the godwits in southwest Friesland occurred on meadows which suffered slightly, yet significantly, less from drought than unused grasslands (Fig. 4). However, during the postbreeding period, the godwits concentrated at meadows where little change in plant growth had occurred during the drought (Fig. 3d & Fig. 4). We note also that southwest Friesland suffered more from the drought than Friesland as a whole (comparison of the two right bar in Fig. 4).

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Figure 4. The effect of the summer drought measured as a loss in greenness (y-axis) was less in fields in southwest (ZW) Friesland used by godwits in the establishment and early nesting period (first column) than in southwest Friesland as a whole (third column). This effect was quite a bit stronger in the distribution of postbreeding godwits (second column). Note also that the effects of drought were more severe in southwest Friesland (third column) than in Friesland as a whole (fourth column). If the capital letters above the bars are different, the categories are statistically significantly different from each other.

The preference of Black-tailed Godwits for fields in southwest Friesland that, later in summer, suffered the least from the drought of 2018, suggests that the godwits are indicating fields with healthy ‘working’ soils, where capillary processes allow the groundwater to reach the plants even when water tables are low. Godwits indicate drought-resilient grasslands.

References

Beintema, A. J. (1986) Man-made Polders in The Netherlands: A traditional habitat for shorebirds. Colonial Waterbirds 9, 196-202.

Howison, R. A., Piersma, T., Kentie, R., Hooijmeijer, J. C. E. W. & Olff, H. (2018) Quantifying landscape-level land-use intensity patterns through radar-based remote sensing. Journal of Applied Ecology 55, 1276-1287.

Kentie, R., Both, C., Hooijmeijer, J. C. E. W. & Piersma, T. (2015) Management of modern agricultural landscapes increases nest predation rates in Black‐tailed Godwits Limosa limosa. Ibis 157, 614-625.

Kentie, R., Senner, N. R., Hooijmeijer, J. C. E. W., Márquez-Ferrando, R., Masero, J. A., Verhoeven, M. A. & Piersma, T. (2016) Estimating the size of the Dutch breeding population of Continental Black-tailed Godwits from 2007 – 2015 using resighting data from spring staging sites. Ardea 104, 213-225.

 

 

 

Report published: Black-tailed Godwit Demographic Project – spring migration of Black-tailed Godwits in Iberia 2017

Jos Hooijmeijer reports:

In January and February 2017, our teams were present again in the Iberian ricefields to look for colour-ringed Black-tailed Godwits. And with great success: despite the lower total numbers, we never saw so many birds with colour rings.

More than 3842 resightings were done of 1187 individual birds; and that just of godwits from our own scheme…… That is an incredible 72% of our colour-ringed population that was alive at that time!

Some of you might have received re-sightings from your own scheme during this trip.

Please have a look at the report for an impression of the field work and the situation last winter. We hope to go back again in 2018; it is addictive you know…..

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Amalia is back in Africa – but what happened to his brood?

Jos Hooijmeijer reports on 7 September 2017:

Amalia is back in Africa! He is in Senegal, in the wetlands and rice fields of  the Casamance (see map).  Amalia is a satellite-tagged male Black-tailed Godwit who’s claim-to-fame is that we are now following him for four and half years!

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Amalia in March 2016: he has just arrived in The Netherlands and getting ready for the breeding season. Note the antenna of his solar-powered satellite transmitter. Photo: Ep van Hijum

He is carrying a transmitter since 2013, the longest of all godwits we track. He actually is a superstar in Friesland, The Netherlands, where his arrival each year is awaited and celebrated by the local community and school classes – including a contest to predict his arrival date. Through satellite tracking we are learning a lot about ‘our’ Godwits, and especially multi-years tracks such as from champion Amalia, are extremely valuable.

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This year Amalia again spent the breeding season in Friesland, The Netherlands. That was no surprise: he has come back to the breeding grounds in Friesland for five years now.

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Amalia in Friesland, The Netherlands on 9 May 2014. Photos: Jos Hooijmeijer

What was a nice development this year is that on 27 May 2017 Jos Hooijmeijer reported that Amalia was seen with very young chicks!. You can read about it here. He apparently found a mate and together they hatched a brood.

What happened to the precious brood Amalia was guiding in May?

Based on Jos’ visit in May we estimated that the laying date has been around 25 April . That is quite early and probably this was his first clutch in 2017. Jos again visited the breeding site of Amalia in Friesland on 9 June 2017, when the chicks would be about 20 days old.

Jos found Amalia only a few hundred meters from where he saw Amalia and his family on 27 May. Amalia’s mate was leading two or three chicks through a pasture grazed by horses and Amalia was sitting on a pole, a good lookout to watch over them.

The chicks were not captured and ringed, so we cannot say with 100% certainty whether they fledged or not. However, if indeed on June 9th there were two or three chicks that survived for 20 days, there is a fair chance that at least one will have survived for 25 days, to the age of fledging.

Amalia sites 2017One of the last observations of Amalia in The Netherlands was on 15 July 2017. That day he was seen by Jelle Loonstra near the town of Jeth, in a group of nine adults and 12 recently fledged juvenile birds. Maybe one of more of these fledglings were his own chicks!

The next day, Amalia was still in Jeth, but he left soon after because on the 18th he had arrived in SE  England, in the estuary of the River Alde (NW of Ipswich). The same day he flew back to the mainland, to the Hoge Plaeten in de Westerschelde bij Breskens (The Netherlands).

From Breskens, he started his southward migration. On 20 July, he was in the vast “marais” wetlands south of Rochefort in Charente Maritime (France), a well-known stopover for Black-tailed Godwits, especially in spring. There he stayed until the end of July or early August (he was 10 days of the radar), to fly to the Casamance in southern Senegal where he arrives on August 12, as in previous years. He is not only faithful to his Friesian breeding area but also to his Senegalese wintering area.

Amalia in Senegal11-9-2017
Amalia is his wintering area in Casamance in southern Senegal, where he arrives on August 12, as in previous years.

 

 

 

Amalia has chicks!

Jos Hooijmeijer reports on 27 May 2017:

After 4 years without breeding success, there seems to be a chance that Amalia will successfully raise young. Amalia is the most famous Black-tailed Godwit in Friesland, or even The Netherlands. In 2013, he was issued a satellite transmitter in the town of Amalia in Spain, and since then we have known his whereabouts from day-to-day (see Follow the Godwits). He probably has been breeding his entire life on the same field on the farm of the Stremler family at the Froonackerdyk in the town of Easterlittens.

This afternoon I again visited the farm and as usual I asked the farmer for permission to look for Amalia. Of course permission was granted, the farmer and his family know I show up every year. When I walked into the field it was fairly quiet; only a single pair of godwits was chasing a crow and approached me, loudly alarming. Unfortunately neither of  the birds had a visible antenna, so they certainly did not carry a satellite transmitter. I walked through the high grass with patches of flowering Meadow Buttercups Ranunculus acris and a some late Cuckoo Flowers Cardamine pratensis. I even saw a Small Heath Coenonympha pamphilus, a sign that the management of this field has no negative effects on butterflies and other insects as in many other places.

At the far end of the field, suddenly three pairs of godwits emerged from the high grass and one of them was Amalia! The transmitter on his back was still in place and the bird looked great. Looking at the colour rings on his legs I could confirm  that this really was Amalia. With the typical fluttering flight of godwits guiding broods he indicated, with hanging legs, where approximately his chicks would be hiding. But I did not get to see them. The grass was high and probably the chicks were still very small.

This encouraging observation is no guarantee that Amalia will end this breeding season with a successfully raised brood. The naked numbers show that only one out of 20 chicks will fledge and survive the difficulties of their first year of life. Mowing machines, the lack of insects and a wide range of predators make life a challenge for chicks growing up in farmland. Fortunately, the breeding site of Amalia has not been mowed yet , and in the immediate vicinity of this field there is still a lot of non-mowed land, and fields with grazing live stock. Will Amalia and his partner succeed? After a day or ten we look again!

Amalia