Most of the blog
entries for this year have somehow focused on the fieldwork aspects of the research I have
been conducting focused on the impact of climate change on Fynbos
endemic birds, starting with the adventure by bicycle across the
biome.
At the beginning of
October I finished my winter survey across Protea, Erica and Restio
dominated habitats of the Fynbos biome. I spent most of October
entering data, and starting some preliminary analysis for a talk
presented by my supervisor Phoebe Barnard at the Pan-African
Ornithological Conference just finished in Arusha, Tanzania. Annelise
Vlok then invited me to give a talk at the Gouritz Cluster Biosphere
Reserve quarterly meeting, and knowing that she is concerned about
the fate of certain Protea species with frequently returning fire
intervals in the Boland area, I decided to push on with analysis of
the impact of fire on Fynbos birds. After all, climate change means
not only an increase in temperature, but also for the winter rainfall
areas we have already recorded a decrease in annual rainfall over the
last 15 years (although I'd be hard pressed to convince anyone of
that this year with record high rainfall! - but such the issue
between weather and climate). A drier climate means an environment
more prone to fire.
In fact, Tineke Kraaij,
who did her PhD at Port Elizabeth has recently published 2 papers on
fire and weather on the eastern Fynbos. There are her findings in a
nutshell:
1. Fynbos is fire prone
and fire adapted, with the frequency, season and intensity of fires
being important determinants of vegetation structure and composition
2. She cites a paper
that says fire return intervals are from 8 to 40 years
3. In western sections,
best fynbos recovery occurs after summer or autumn fire, while in the
eastern Fynbos fire patterns are aseasonal. However, existing
guidelines for the management of fire in fynbos are largely based on
research carried out in the west.
4. Lightning causes 59%
of fires, and she used data to calculate trends in a Fire Danger
Index (FDI).
5. Mean annual FDI has
increased since 1939
6. Large fires have
increased in the south - eastern CFK
8. Frequent recurrence
of very large fires and the virtual absence of vegetation in older
postfire age classes are potential causes for concern in achieving
fynbos conservation objectives
Basically, we have 2
nectarivores: Cape Sugarbird and Orange-breasted Sunbird; 2 seed
eaters: Cape Siskin and Protea Seedeater; and 2 insectivores:
Victorin's Warbler and Cape Rock-jumper. All of these are listed by
the IUCN as being species of Least Concern i.e. none are endangered.
However, a review of the South African Bird Atlas Project (SABAP2)
data shows that 2 species meet IUCN criteria for vulnerable – Cape
Rock-jumper and Protea Seedeater due to a decrease in reported range
>30% and this range is close to 20 000 square kilometers, another
criteria for vulnerable. The thing is, these are mountain birds, so
there is some concern that people who submit lists may not be getting
into mountains. However, since I am looking at similar protocols, why
were they reported for these sites previously? An article reviewing
the data can be read here:
http://oo.adu.org.za/content.php?id=36
So in order to really
understand what was going on, what was needed was a survey through
the mountains by one observer to avoid observer bias, with a
repeatable protocol. So I jumped on my bike and travelled 2500km to
check out the situation. The following is a map of the points I
conducted, highlighting the occurrence of Cape Sugarbird along the
way. I did over 800 points. The pink area are selected bioregions of the
Fynbos that includes mountain Fynbos, and excludes renosterveld
habitats. This area is around 56 000 square kilometers.
For the analysis on
fire, I use around 500 points that I had data for at the time I
started to analyse the impact of fire, so it is not the complete data
set. However, it does include points conducted in both winter and
summer surveys in some cases. I did this to improve the number of
encounters for calculating bird density in the Distance 6.0 program,
which needs lots of encounters to figure out how many birds there
are.
I should stress these
data are preliminary – they have not yet been peer-reviewed and a
final analysis will include all the data points, not just the data
that was ready at the time the first analysis were needed. However, I
feel the trends have been identified.
So the first chart is
the distribution of Fynbos age, as determined using growth rings on
Protea species. For simplicity, I've grouped the data into 4 age
categories, and a mixed category for points where different fire
histories were clearly present at a site. This chart shows that there
are fewer areas with old Fynbos – so few for 20 years or more I had
to lump them into the category of 15 years or more in order to run
the density analysis.
This chart shows the
average number of species I recorded per point. This was lowest for
the youngest age class, around 2, and higher for points were age was
greater than 10.
To show that these few
species are not dominating the landscape, the following chart shows
bird density for all the birds that were recorded during the survey.
Again, bird density was lowest for the youngest age class, and
greatest for the oldest age class.
Of all the over 3000
bird group encounters analysed, 12 species made up 62 percent of
these. So the Fynbos is dominated by a handfull of species. Of these,
four were considered Fynbos endemics. The following series of charts
shows bird density by species for these four – where there was
enough data to analyse. There were not enough group encounters to do
this analysis for Cape Rock-jumper and Protea Seedeater. The
strongest relationship is shown for Cape Sugarbird – where density
is strongly correlated to Fynbos age. Cape Siskins on the other hand
don't seem to care. Victorin's Warbler are happy once age since fire is greater than 5 years.
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| Orange-breasted Sunbird density in relation to fire age categories |
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| Cape Sugarbird density in relation to fire age categories |
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| Cape Siskin |
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| Victorin's Warbler |
Lastly, this chart
shows relative capture rates of birds in mist nets from Blue Hill
Nature Reserve grouped according to dietary guild. All bird groups
were captured less frequently, with nectarivores the most impacted.
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| Relative capture rates of Fynbos bird species in burnt and unburnt Fynbos (standardised by 1000meters of net hours). |
