Blog by Derek Gruar, Senior Research Assistant, RSPB Centre for Conservation Science
Here at RSPB Hope Farm we undertake a summer monitoring programme every year to measure how our bird and butterfly populations change in relation to our wildlife friendly farm management. Bird monitoring begins at the end of March and runs until the first week of July, with between 8 and 12 surveys of the whole farm completed. For each survey, I walk every hedgerow and field boundary on the farm and map the locations of all bird activity (singing, alarm calls, nest building) using Common Bird Census (CBC) methods.
Surveying starts 30 minutes after sunrise and can take 3-5 hours depending on bird activity, to cover the 180ha of the whole farm it takes two mornings. Therefore, on one morning I survey the north of the farm and the next day the southern section. In addition to all the resident birds on the farm, I am occasionally lucky enough in April and May to find some passage migrants heading further north, in 2017 these included several ring ouzels, redstarts and wheatears.
At the end of the survey season, I produce territory maps for all species seen on the farm. Each of the different survey visits are designated a letter A to L (for 12 visits) and on each species map, I allocate the associated letter code to where that individual bird was seen. The map below shows an area with several yellowhammer territories. Letters in circles are singing males, dotted lines indicate two different birds recorded simultaneously and a solid line indicates the movement and direction of the same bird.
Image: An area with several yellowhammer territories monitored at Hope Farm
From these maps, we determine the number of territories for every bird species on the farm each summer. We specifically monitor a group of species designated as Farm Bird Index species by DEFRA; here we combine the individual species trends into a single index to give a figure of average change in these species compared to the first year we owned the farm.
226% average increase compared to 2000
This summer we recorded 271 territories of 16 farm index species (see table below), compared to only 117 territories of 10 species in 2000. Over the past 17 years, we have seen increases in all index species with grey partridge, lapwing and corn bunting colonising the farm during this time. Turtle dove used to occur on an irregular basis but has been absent for a few years. The only declining species is greenfinch, probably because of the Trichomonas gallinae infection that has affected the population nationally. The Hope Farm population after a decline seems to have stabilised over the past few years.
Table: Species in red text are those that have declined nationally by over 50%, amber are relatively stable species and green are increasing since the 1970’s.
The Hope Farm Bird index for 2017 now stands at a record high of 3.26 (or equivalent of 226% average increase compared to 2000).
Graph: The Hope Farm Bird index for 2017 now stands at a record high of 3.26
Butterflies on the farm: 213% increase
As explained in a previous blog, our butterfly monitoring involves walking three set routes across Hope Farm once a week for a 26-week survey season. Surveys start from 1st April and all butterflies in a 2.5-metre radius of the survey route counted. We submit our data to Butterfly Conservation as part of the national butterfly monitoring scheme.
The 2017 season had a slow start with just a few peacock, small tortoiseshells and brimstones on the wing during the cool early surveys. In May, the weather prevented some surveys and this had a knock on effect that butterfly numbers remained low until mid-June, with lower than average counts of early season species such as orange-tip. The summer then decided to appear from late June and for an 8-weeks period butterfly numbers on the farm increased massively; at times, it appeared there were butterflies everywhere.
The summer heat saw very high counts of ringlets, meadow browns and gatekeepers and on 26th June, I found a Purple-Hairstreak a new species for the farm. Other species that seemed to respond well to the warm weather included brown argus, common blue and marbled white these are species that have colonised the farm over the past 17 years and were seen in record numbers. Late summer saw cooler conditions compared to recent years and butterfly counts were subsequently lower with small white being the main stay of counts in August and September. A few of the earlier and later emerging species such as peacock and speckled wood were at lower levels than expected.
As with the bird monitoring data, we produce an index figure that gives a measure of the average change for 24 species found in the wider countryside as determined by DEFRA. The Hope Farm Butterfly index for 2017 now stands at a record high of 3.13 (or equivalent of 213% average increase).
Graph: The Hope Farm Butterfly index for 2017
After such a fantastic summer with record numbers of both birds and butterflies it will be interesting to see what our winter bird counts will yield and we look forward to what we will find in 2018! For further information on Hope Farm monitoring work contact email@example.com
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