The breeding ecology of Breckland Tree Pipits: Niall H K Burton

The breeding ecology of Breckland Tree Pipits Anthus trivialis Report for 2019

Niall H.K. Burton (niall.burton@bto.org) British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU

Report to the Forestry Commission East England Forest District Bird Group Meeting, Santon Downham February 2020

This report presents the latest results of a continuing study of the breeding ecology of Tree Pipits Anthus trivialis undertaken in and around Thetford Forest. The study has encompassed five main elements:

• Territory mapping to assess habitat preferences and monitor numbers; • Nest finding to monitor breeding success; • Colour-ringing to monitor adult survival rates and movements; • Acoustic recording to assess individual variation in song and so also monitor adult survival rates; • A geolocator study to determine the species’ migration routes and wintering areas.

Monitoring breeding success

Year Nests found Young ringed Year Nests found Young ringed

1998 7 11 2009 30 93 1999 27 83 2010 23 67 2000 28 104 2011 28 70 2001 29 121 2012 24 77 2002 27 110 2013 18 42 2003 24 87 2014 24 107 2004 20 61 2015 37 116 2005 16 45 2016 28 95 2006 19 53 2017 30 71 2007 20 66 2018 34 109 2008 33 80 2019 32 114

TOTAL 558 1782

Nest totals include nests found by Ashley Banwell, Gavin Chambers, Greg Conway, Paul Dolman, John Dries, Allan Hale, Ron Hoblyn, Mark Hulme, Simon Pickett, John Secker, Kerry Skelhorn, Mike Toms, John Walshe and Lucy Wright, and data from the BTO’s Nest Record Scheme.

Monitoring survival – colour-ringing and acoustic monitoring

A colour-ringing project was begun in 2009, to look at within- and between-year site-fidelity and survival. To date, 200 adult birds have been colour-ringed: 177 males and 23 females.

Complementing the colour-ringing study, a new study (funded by Mark Constantine) in collaboration with Charles University, Prague, was initiated in 2016 aiming to evaluate the recording of song as an alternative approach to monitoring annual survival.

Existing study has highlighted the variability of Tree Pipit song repertoires, and that individuals can be reliably identified from recordings of ca. five minutes (containing 20+ songs), and thus the potential for acoustic monitoring of movements and return rates of territorial males (Petruskova et al. 2016. Methods Ecol. Evol. 7: 274-284).

The study’s aims are: • To monitor independent samples of individual male Tree Pipits through colour-ringing and acoustic recording; • To use standard mark-recapture analyses to generate and compare annual survival rates from the two approaches.

Study plots within the forest have thus been divided into those in which birds are being monitored by acoustic recording alone and those in which birds are being monitored through colour-ringing. Since 2016, 86 individuals have been identified through acoustic recording alone on acoustic recording plots.

Apparent annual adult survival for male Tree Pipits in Thetford Forest, based on colour-ring re-sightings (black) and acoustic recording (red) Male Tree Pipit ‘LBW,C;RBP,M’ King’s Forest 17.04.2018

Migration routes and wintering areas

The Tree Pipit is red-listed on the latest list of UK Birds of Conservation Concern (Eaton et al. 2015) and is also listed as a species of principal importance in England under Section 41 (S41) of the Natural Environment and Rural Communities (NERC) Act. However, there is limited information on the wintering grounds of the British population.

To better understand the migration routes, timing of movements and wintering grounds of British-breeding Tree Pipits and thus potential pressures outside the breeding season, a pilot geolocator project was initiated in Thetford Forest in 2016 with funding from Mark Constantine. In total, 21 geolocators were deployed (14 on males, seven on females). Eight of these birds (six males, two females) returned to the forest in 2017 – a similar return rate to that of colourringed control birds – and geolocators were recovered from four of the males. Data from these geolocators were presented in the report for 2017 and indicated wintering grounds in west Africa, centred on Guinea, Senegal and western Mali.

A further six geolocators were deployed on male Tree Pipits in Thetford Forest in 2018. Support was also provided in 2018 to a project to fit 20 geolocators to Tree Pipits (17 on males, three on females) in the Forest of Dean (funded by the Heritage Lottery Fund). Two of the Thetford Forest birds returned in 2019 and the geolocators were recovered from these birds. Eight tagged birds also returned to the Forest of Dean in 2019 and three further geolocators were recovered. Data from these geolocators indicate that Thetford Forest and Forest of Dean birds winter in approximately the same region of west Africa.

The data have also been used in a paper looking at the desert-crossing strategies of ten AfroPalearctic migrant species across Europe (Jiguet et al. 2019). By looking at the light intensity data recorded by the geolocators, this study has shown that, both in autumn and spring, most individual Tree Pipits stop migrating during the day while crossing the Sahara. However, the majority of individuals prolong their nocturnal migration flights into the morning, while a few may perform non-stop flights across a full day.

Day and night light intensity data (X-axis) from geolocators deployed on two Tree Pipits, showing autumn and spring crossings of the Sahara. Smooth patterns in light intensity indicate periods when birds were migrating. In the first figure, nocturnal migration flights extend into the morning for two successive days. In the second figure, migration flight extends across one and a half days.

From Jiguet et al. (2019)

With particular thanks to Greg Conway, Ian Henderson and Justin Walker, and, in 2019, Mike Toms and Jeff Riches.

Publications:

• Burton, N.H.K. 2009. Reproductive success of Tree Pipits Anthus trivialis in relation to habitat selection in conifer plantations. Ibis 151: 361-372. https://doi.org/10.1111/j.1474919X.2009.00915.x • Burton, N.H.K. 2007. Influences of restock age and habitat patchiness on Tree Pipits Anthus trivialis breeding in Breckland pine plantations. Ibis 149 (Suppl. 2): 193-204. https://doi. org/10.1111/j.1474- 919X.2007.00737.x • Burton, N.H.K. 2007. Intraspecific latitudinal variation in nest orientation among groundnesting passerines: a study using published data. Condor 109: 441-446. https://doi.org/10.1093/condor/109.2.441 • Burton, N.H.K. 2006. Nest orientation and hatching success in the Tree Pipit Anthus trivialis. Journal of Avian Biology 37: 312-317. https://doi.org/10.1111/j.2006.0908-8857.03822.x • Eaton et al. 2015. Birds of Conservation 4: the population status of birds in the Uk, Channel Islands and Isle of Man. Brit Birds 108: 708-746 • Jiguet, F., Burgess, M., Thorup, K., Conway, G., Arroyo Matos, J.L., Barber, L., Black, J., Burton, N., Castelló, J., Clewley, G., et al. 2019. Desert crossing strategies of migrant songbirds vary between and within species. Scientific Reports 9. https://doi.org/10.1038/ s41598-019-56677-4