Each 'X' on the plot represents the reporting rate in each pentade. The red line is the smoothed average reporting rate through the year. The smoothed line is not a formal model, it is simply designed to lead the eye through the data - but it is a sophisticated smoother (thanks to Les Underhill who in fact produced these plots for us).
Starting with a common species which gives an idea just how the
data will show what would be an expected pattern - the Common
Bulbul, a common resident. Here, the reporting rate is high
(65-70% of cards have the bulbul reported on them) and is
consistent throughout the year - i.e. it is resident, numbers
don't fluctuate - just as you would have thought!
A similar pattern is shown by the Woodland Kingfisher - but here the reporting rate is much lower (2-3%) as it is a far less common species than the bulbul:
Looking at well-known migrants, here is a not very surprising overall pattern for a common Palearctic species, the Willow Warbler, but with some very sweet detail within it:
What this immediately tells us is that this is a migrant that
during the middle part of the year (June-Sept) it is entirely
absent from Kenya, that there is a rapid arrival in Oct to late
November with a slight peak in numbers in early December. During
the heart of the northern winter, Willow Warblers are not too
hard to find (c.20% reporting rate) but there is a clear arrival
from the second half of February, presumably of migrants from
the south, when they then become definitely more common in the
northward migration in March / early April before a rapid
departure with all gone by the end of May (and the steepness of
the slope tells us the departure is more rapid than the arrival
in October - i.e. the birds disappear in a shorter period than
they arrive).
These are awesome results showing in hard figures that Willow Warblers are most numerous during the northward migration - something any of us who've done any serious brrding in Kenya will know... but to have hard data showing it is superb. This suggests that on their way south a number must either overfly Kenya without stopping or migrate farther west - as is known to happen strongly in other species such as Red-backed Shrike. An area for more study...
Another really interesting pattern of a migrant, this time an Afrotropical species, is for the Red-capped Robin Chat:
This is the opposite pattern to the Willow Warbler as it
migrates south to breed during our summer - December-March -
when you can see it is absent. One or two start to appear in
March but there is a rapid arrival in May and apparently a
second arrival in July - or, given it comes to a sharp peak
towards the end of August, this would appear as a passage of
birds since the reporting rate then drops off steadily through
to the end of the year. An awesome picture of this species'
seasonality, no? It raises interesting questions for further
research - e.g. if there is a passage of birds, where are they
on passage from?
Some may know that there are, in fact, resident populations of
Red-capped Robin Chat as well, mostly inland - which has not
been picked up by the data. This is because they are far
commoner on the coast where they are a clear migrant and so
these are the ones that have been reported so far. For the
inland resident populations you have to go looking hard to find
the species and so we need more observations, more records to
show this - i.e. more birders out there joining in on what is
definitely going to be the key bird conservation project of the
next 10 to 20 years for Kenya.
These results have been produced from what are actually
relatively very small amounts of data - which shows the huge
strength of the bird atlas protocol - simple, yet tight,
producing very analysable data. The protocol is simply: within a
single atlas square, min of 2 hours focussed birding over a five
day period (a pentade...) and record all species in the order
you encounter them noting the total seen after each hour of
birding.
The potential for digging out a wide range of extremely
relevant and important patterns for bird conservation is
enormous - with sufficient data you can produce the same plots
as above but annually to see any changes in migration pattern
over time (possibly caused by climate change, for e.g.); species
that are under threat - e.g. vultures - will show over time an
overall decrease in reporting rate, proving beyond doubt that
there IS a problem..., when government takes action and they
start to recover (here's hoping!), then the atlas data will pick
this up and show it.
These plots are taking data from the whole of Kenya - with
sufficient data, you can do the same analysis for a given area
(e.g. a ranch, a conservation area), even just a single pentad
and see local patterns of phenology (e.g. dry season movements).
The possibilities go on and on. If you are at all interested in
birds and their conservation in Kenya, please do join us in this
exciting project. The protocol is simple and actually a heck of
a lot of fun to do, it hones your birding skills even further
and gets to be quite addictive (perhaps there should be a
warning put on it?!).
Write to Sidney at kenyabirdmap@naturekenya.org to register or
for more information.
And THANK you to all those who have contributed so far for
being a part of this awesome project!
Colin