A STUDY ON QUANTITIES OF BIRDS VISITING INVASIVE PROSOPIS
TREES COMPARED TO NATIVE TREES
The impact of prosopis
trees on Namibian bird life
Photos und text by Stefan Rust
2013
(In terms of the Geneva Convention the copyright of these texts belong to
Stefan Rust)
The ubiquitous
Prosopis tree
Preface
This study was carried out in Namibia. The necessary funds
for the field trips I draw from BirdsConTour (Birds Conservation &
Tourism), my own business. Some field works I did while being on tour as a guide
for Pack Safari and Chamäleon Reisen. I am grateful for this opportunity.
In particular I want to express my gratitude to my father,
Mr. Argo Rust. His interest and support throughout the entire research process
was of utmost importance for the outcome of this study.
I want to express my deepest gratitude to my life companion
Birgit, who has been a great support during the entire process. Her positive
attitude and encouragement enabled me to enjoy this study.
I dedicate this scientific work to my daughter, Leni, who
was born on the 16th of October 2009.
Windhoek, December 2013
Stefan Rust
Aim of the study
The aim of this study was to investigate and evaluate the
influence of the Prosopis tree on wild birds in Namibia, so as to provide
scientific research-based guidelines for management of the prosopis invasion.
Fact file
(Mesquite is) “the devil with roots. It scabs my cows,
spooks my horses, and gives little shade.”
This is the opinion of W.T. Waggoner, a pioneer northwest
Texas rancher, about prosopis trees.
This mesquite, as it is commonly known in America, is a
species of small to medium-sized flowering tree in the pea family, Fabaceae.
Prosopis, its generic name, means “burdock” in Latin.
Containing of about 45 species, they often thrive in arid
soil and are drought resistant and 90% of them are native to Latin America,
principally Argentina and Chile.
The southwestern Native Americans used the seed as a food
source. The seeds contain as much as 30% sugar and, when fermented, produce an
alcoholic beverage. A meal made from the seeds was also used by Native
Americans to make bread.
Prosopis were introduced around late 1800’s to South Africa
to provide fodder and shade for livestock. Most probably from 1920 onwards
mostly farmers from South Africa settling in Namibia brought several species to
Namibia.
- It adapts to almost any soil.
- Seeds can lie dormant for many years, up to 40 years,
until conditions are right to
sprout.
- Taproots seemingly can grow as deep as needed to reach the
water table. Incidents
of up to 50
meters in length occurred, and the lateral roots can fan out up to 20
- When seed is swallowed, the seed parasites die when
exposed to the animals’ gut
juices and the
seeds find moisture and nutrients in the animals’ dung – a perfect
formula for
expansion.
Problem statement
Overutilizing (overgrazing) and underutilizing, whether done
by cattle, sheep or goats, strips native grasses from the land, leaving it bare
and open to bush invasion. Over time prosopis even outcompete native trees and
bushes, leading to a mesquite (prosopis) encroachment.
Landowners are frustrated and consider it a noxious weed,
whose thorns injure livestock. Worst of all, its extensive root system uses
more than its fair share of water, which otherwise could grow livestock
nourishing grasses.
My saying is: Some landowners sow with mismanagement of
their land; now they are reaping thickets of bushes (in this case prosopis)
that are stabbing thousands of hectares of land into non-productiveness.
According to scientists prosopis flourishes on 10 000
hectares in Namibia and made it unusable for livestock. In Texas, the
ubiquitous prosopis grows on at least one-third of the land area of the state.
Under natural circumstances these trees do not provide much
shade. A traveler once said that “to find shade under a mesquite tree is like
dipping water with a sieve.”
Research methodology
In an effort to understand what influence the expansion of
the invasive prosopis tree has on local wild birds, this study concentrated on
the frequency of birds visiting (using) prosopis trees in comparison to native
trees for resting, sleeping, feeding, breeding, dust bathing (on ground under
tree) and socializing.
Observation took place over a time span of one year and
allover Namibia, aiming to make this research as reliable and comprehensive as
possible.
To keep the necessary distance to the observed trees but
still be able to identify the different birds visiting, strong and reliable
optic was used. In this study I used a Swarovski EL 8,5 x 42 binocular and a
Hawke Nature spotting scope HT 3651
- 20 – 60 x 60 for
observation.
To reduce the irritation factor, only one person, the
observer himself (me), was on site.
This list shows all the studied sites in an alphabetical
order.
A-little-Sossus Lodge (Sossusvlei surrounding)
Avis (Windhoek)
Avis dam (Windhoek)
Avis Riding premises (Klein Windhoek)
Brent Carlsson Str. (Windhoek)
Harmony Centre (Aris, Windhoek)
Kalahari Anib Lodge (Mariental)
Kalahari Farmhouse (Stampriet)
Klein Aus Vista Lodge (Aus)
Lake Oanob Resort (Rehoboth)
UNAM (University of Namibia) (Windhoek)
Western Bypass (corner Kupferbergpass Road) (Windhoek)
At the Kalahari Anib Lodge I completed my very first field
study after this study kicked off. On that day the temperature was 42 degrees
Celsius
What was done and data collection
At all field study sites one prosopis and one native tree
were compared with each other over a certain time through counting how many
wild birds visited each of the two trees.
In choosing two trees to use for the study, some criteria
were taken into consideration. Both trees needed to have/be:
- growing more or less in neighborhood to each other.
- same circumference (height/size).
- same habitat.
- equal access by animals.
- equal treatment/management (e.g. bushfire etc.).
During the time of observation each individual wild bird
visiting one of the two chosen trees was noted by writing down the species name
and behind the name following quantities.
A bird qualified for a visit when it
- came to rest in the tree
- came to rest under the tree
- came to rest on top of the tree
- came to feed in the tree
- came to feed under the tree
- came to feed on top of the tree
- came to sleep in the tree
- came to sleep under the tree
- came to sleep on top of the tree
- came to breed in the tree
- came to breed under the tree
- came to breed on top of the tree
- came to perch in the tree
- came to perch under the tree
- came to perch on top of the tree
- came to sunbath in the tree
- came to sunbath under the tree
- came to sunbath on top of the tree
- came to socialize in the tree
- came to socialize under the tree
- came to socialize on top of the tree
- came to collect nesting material in the tree
- came to collect nesting material under the tree
- came to collect nesting material on top of the tree
- came to dustbath under the tree
- passed the tree nearby (±1m) to catch prey in the air
- passed the tree nearby (±1m) to catch nesting material in
the air
- passed the tree nearby (±1m) to chase another bird or
other animal away
- left the tree premise or tree periphery and returned
On some field study sites bird life was observed in dense
stands of prosopis trees and compared to bird life in dense stands of native
trees.
These three Crowned Lapwings qualify for bird visits because
they make use of the shadow of the tree on the ground
Analysis of the collected research data
Analysis of the collected material continued during the
whole period of the fieldwork. After the observation of each site a table was
established and a percentage of visits to the prosopis tree was calculated by
taking the amount of visits to the native tree (compared tree) as standard. For
the final results an overall average was figured to be able to pinpoint the
impact of the prosopis tree specie on Namibian bird life.
What was found (Results)
The tables show that local birds use prosopis trees only by
18% in comparison to native trees!
Table No. 1
Location of site:
Kalahari Anib Lodge, Mariental
Date of observation: 27th
January 2013
Time of observation:
11:00
Weather conditions:
Sunny, 42 degrees Celsius
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Lark-like Bunting
1
2
resting under
tree
Marico Flycatcher
1
Grey-backed Sparrow-lark
2
resting in tree
Total
Species: 4
Native tree: 22
Prosopis: 4
Result:
------------
% 18,18 bird
visits to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------
Location of site:
Brent Carlsson Road, Windhoek
Time of observation:
11:35 – 11:50
Weather conditions:
Sunny, 35 degrees Celsius
Trees compared:
Black-thorn Acacia and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird Amount
of bird visits to
Reason for visit
Black-thorn Acacia
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
White-browed Sparrow-weaver 2
Cape Glossy Starling
2
Black-chested Prinia
1
perching on top
of
tree
Total
Species: 3
Native tree: 4
Prosopis: 1
Result:
------------
% 25 bird visits to Prosopis
tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 3
-------------------------------------------------------------------------------------------------------
Location of site:
UNAM (University of Namibia), Windhoek
Date of observation:
1st February 2013
Time of observation:
12:35 – 13:35
Weather conditions:
Sunny, 35 degrees Celsius
Trees compared:
Black-thorn Acacia and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Black-thorn Acacia
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Fork-tailed Drongo
1
2
perched in tree
Black-chested Prinia
2
perching on top
of tree
Dusky Sunbird 4
4
feeding
Scarlet-chested Sunbird
1
Long-billed Crombec
1
Southern Masked-Weaver
2
2
brief
rest
White-browed Sparrow-weaver 12
7
resting in and
mainly feeding
under
tree
Pale-winged Starling
2
White-backed Mousebird
2
Rock Martin
3 1
feeding over
Tree
African Red-eyed Bulbul
2
Total
Species: 11
Native
tree: 30
Prosopis: 18
Result:
------------
% 60 bird visits to Prosopis tree
in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 4
-------------------------------------------------------------------------------------------------------
Location of site:
Western Bypass corner Kupferbergpass Road, Windhoek
Date of observation:
3rd February 2013
Time of observation:
9:10 – 9:20
Weather conditions:
Sunny, South wind
Trees compared:
Umbrella Thorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Umbrella Thorn Prosopis to
Prosopis
-------------------------------------------------------------------------------------------------------
Black-faced Waxbill
2
Total
Species: 1
Native tree: 2
Prosopis: 0
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 5
-------------------------------------------------------------------------------------------------------
Location of site:
Harmony Centre, Aris, Windhoek
Date of observation:
3rd February 2013
Time of observation:
10:00 – 10:30
Weather conditions:
Sunny, South wind
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
White-browed Sparrow-weaver 2
Total
Species: 1
Native tree: 2
Prosopis: 0
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 6
-------------------------------------------------------------------------------------------------------
Location of site:
Klein Windhoek Riding premise, Avis, Windhoek
Date of observation:
5th February 2013
Time of observation:
11:45 – 12:20
Weather conditions:
Sunny, South wind
Trees compared:
Sweet thorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Sweet thorn
Prosopis
to Prosopis
-------------------------------------------------------------------------------------------------------
Long-tailed Paradise-Whydah 1
1
perching briefly
on top of tree
Rock Martin
1
Violet-eared Waxbill
1
White-browed Sparrow-weaver 4
feeding under
Tree
Laughing Dove
1
Southern Masked-Weaver
1
Total
Species: 6
Native tree: 5
Prosopis: 5
Result:
------------
% 100 bird visits to Prosopis tree in
comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 7
-------------------------------------------------------------------------------------------------------
Location of site:
Avis, Windhoek
Date of observation:
5th February 2013
Time of observation:
12:40 – 13:00
Weather conditions:
Sunny/Cloudy
Trees compared:
Black-thorn Acacia and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird Amount
of bird visits to
Reason for visit
Black-thorn Acacia
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Chestnut-vented Tit-babbler
1
Total
Species: 1
Native tree: 1
Prosopis: 0
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 8
-------------------------------------------------------------------------------------------------------
Location of site:
Avis dam, Windhoek
Date of observation:
6th February 2013
Time of observation:
08:15 – 09:25
Weather conditions:
Sunny, a few raindrops last night
Trees compared:
Sweet thorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Sweet thorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Swallow-tailed Bee-eater
2
perching on side
of
tree
Marico Sunbird
1
Rock Martin
1
Greater Striped Swallow
1
Rattling Cisticola
3
2
chasing each
other through
tree
Grey Go-Away-Bird
1
Total
Species: 6
Native tree: 7
Prosopis: 4
Result:
------------
% 57,14
bird visits to Prosopis tree in comparison to standard tree (native
tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 9
-------------------------------------------------------------------------------------------------------
Location of site: Lake
Oanob Resort, Rehoboth
Date of observation: 22nd
March 2013
Time of observation:
17:15 – 18:15
Weather conditions:
Sunny, a few clouds
Trees compared:
Worm-cure tree and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Worm-cure tree Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Dusky Sunbird
1
1
perching on side
of
tree
Southern-masked Weaver
1
feeding on tiny
Buds
Rock Martin
1
Total
Species: 3
Native tree: 2
Prosopis: 2
Result:
------------
% 100 bird visits to Prosopis tree in
comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 10
-------------------------------------------------------------------------------------------------------
Location of site:
Lake Oanob Resort, Rehoboth
Date of observation:
23rd March 2013
Time of observation:
15:30 – 16:00
Weather conditions:
Sunny, cloudy
Trees compared:
Black-thorn Acacia and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Black-thorn Acacia
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Dusky Sunbird
1
Southern Grey-headed
Sparrow 1
Total
Species: 2
Native
tree: 2
Prosopis: 0
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 11
-------------------------------------------------------------------------------------------------------
Location of site:
A-little-Sossus Lodge, nearby Sossusvlei
Date of observation:
8th April 2013
Time of observation:
14:45 – 15:30
Weather conditions:
Sunny
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Laughing Dove
2
Common Fiscal
1
Dusky Sunbird
2
2
feeding in tree
Total
Species: 3
Native tree: 5
Prosopis: 2
Result:
------------
% 40 bird visits to Prosopis
tree in comparison to standard tree (native tree)
------------
Table No. 12
-------------------------------------------------------------------------------------------------------
Location of site:
Kalahari Farmhouse, Stampriet
Date of observation:
13th April 2013
Time of observation:
6:00 – 6:30
Weather conditions:
Cloudy
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
African Red-eyed Bulbul
7
Acacia Pied Barbet
5
Pearl-spotted Owlet
1
House Sparrow 1
perching and
singing
Total
Species: 4
Native
tree: 13 Prosopis: 1
Result:
------------
% 7.69 bird visits to Prosopis tree in
comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 13
-------------------------------------------------------------------------------------------------------
Location of site:
A-little-Sossus Lodge, nearby Sossusvlei
Date of observation:
7th May 2013
Time of observation:
17:00 – 17:30
Weather conditions:
Sunny and thin clouds (like mist)
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits
to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
African Red-eyed Bulbul
1
perching
Familiar Chat
1
Dusky Sunbird
4
2
perching and
squabbling
Total
Species: 3
Native tree: 5
Prosopis: 3
Result:
------------
% 60 bird
visits to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 14
-------------------------------------------------------------------------------------------------------
Location of site:
A-little-Sossus Lodge, nearby Sossusvlei
Date of observation:
3rd June 2013
Time of observation:
16:00 – 16:30
Weather conditions:
Sunny and windy, slightly cooler
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Fork-tailed Drongo
1
Rock Martin
1
Total
Species: 2
Native tree: 2
Prosopis: 0
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 15
-------------------------------------------------------------------------------------------------------
Location of site: Kalahari
Anib Lodge, nearby Mariental
Date of observation: 7th
of June 2013
Time of observation:
16:15 – 16:45
Weather conditions:
Sunny and windy
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Black-chested Prinia
3
Pririt Batis
2
Rock Martin
2
Total
Species: 3
Native tree: 7
Prosopis: 0
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 16
-------------------------------------------------------------------------------------------------------
Location of site: A-little-Sossus
Lodge, nearby Sossusvlei
Date of observation: 14th
of August 2013
Time of observation: 15:00
– 16:00
Weather conditions:
Sunny and slightly windy
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Familiar Chat
3
1
perching
Rock Martin
2
Total
Species: 2
Native tree: 5
Prosopis: 1
Result:
------------
% 20 bird visits to Prosopis
tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 17
-------------------------------------------------------------------------------------------------------
Location of site: Klein
Aus Vista Lodge (Aus)
Date of observation: 15th
of August 2013
Time of observation: 15:00
– 16:00
Weather conditions: Sunny,
windy, chilly
Trees compared: Camelthorn
and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Layard’s Tit-Babbler
2
Mountain Wheatear 4
Laughing Dove
1
Cape Sparrow
2
White-throated Canary
4
Total
Species: 5
Native tree: 13 Prosopis: 0
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 18
-------------------------------------------------------------------------------------------------------
Location of site: Kalahari
Farmhouse, Stampriet
Date of observation:
18th of August 2013
Time of observation:
16:45 – 17:30
Weather conditions:
Sunny, slightly cloudy, chilly
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Laughing Dove
39
House Sparrow 9
Golden-tailed Woodpecker
1
African Red-eyed Bulbul
1
Yellow Canary
1
Briefly sitting
Total
Species: 5
Native
tree: 50
Prosopis: 1
Result:
------------
% 2 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 19
-------------------------------------------------------------------------------------------------------
Location of site: A-little-Sossus
Lodge, nearby Sossusvlei
Date of observation: 30th
of September 2013
Time of observation: 15:00
– 17:00
Weather conditions:
Sunny, strong eastern wind
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount
of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Rock Martin
1
Sabota Lark
1
Southern Masked-Weaver
3
Pale-winged Starling
1
Total
Species: 4
Native tree: 6
Prosopis: 0
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 20
-------------------------------------------------------------------------------------------------------
Location of site: Kalahari
Farmhouse, Stampriet
Date of observation:
4th of October 2013
Time of observation:
17:30 – 18:15
Weather conditions:
Sunny
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Laughing Dove
23
House Sparrow
12
1
Common Scimitarbill
1
1
Rock Martin
4
Cape Sparrow
7
Marico Sunbird
1
Black-throated Canary
1
Southern Masked-Weaver
1
1
African Palm-Swift
7
Total
Species: 9
Native tree: 55
Prosopis: 5
Result:
------------
% 9.09 bird visits to Prosopis tree in comparison
to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 21
-------------------------------------------------------------------------------------------------------
Location of site: A-little-Sossus
Lodge, nearby Sossusvlei
Date of observation:
8th of October 2013
Time of observation:
18:00 – 19:00
Weather conditions:
Cloudy and windy
Trees compared:
Camelthorn and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn
Prosopis to Prosopis
-------------------------------------------------------------------------------------------------------
Cape Sparrow
4
Total
Species: 1
Native tree: 4
Prosopis:
Result:
------------
% 0 bird visits
to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Table No. 22
-------------------------------------------------------------------------------------------------------
Location of site: A-little-Sossus
Lodge, nearby Sossusvlei
Date of observation: 17th
of November 2013
Time of observation: 17:00
– 18:00
Weather conditions: Sunny
and windy
Trees compared: Camelthorn
and Prosopis
-------------------------------------------------------------------------------------------------------
Visiting bird
Amount of bird visits to
Reason for visit
Camelthorn Prosopis to
Prosopis
-------------------------------------------------------------------------------------------------------
Cape Sparrow
4
Dusky Sunbird
1
Laughing Dove
2
Cape Turtle-Dove
2
Total
Species: 4
Native tree: 9
Prosopis:
Result:
------------
% 0
bird visits to Prosopis tree in comparison to standard tree (native tree)
------------
-------------------------------------------------------------------------------------------------------
Total overview calculation
All Prosopis visit percentages added
% 18,18
(Table 1)
%
25
( 2)
% 60
( 3)
% 0
( 4)
% 0
( 5)
% 100
( 6)
%
0
( 7)
% 57,14
( 8)
%
100
( 9)
% 0
( 10)
% 40
( 11)
% 7,69
( 12)
% 60
( 13)
% 0
( 14)
% 0
( 15)
%
20
( 16)
% 0
( 17)
%
2
( 18)
% 0
( 19)
% 9.09
( 20)
% 0
( 21)
% 0
( 22)
––––––––––
499,10
divided through numbers of tables
22
––––––––––
gives % of bird visits to Prosopis trees
in comparison to native trees
% 22,69
––––––––––
Why do birds prefer visiting native trees instead or
equally prosopis trees
Native trees offer:
- Stronger top twigs that makes perching on them more
comfortable.
- Better nesting possibilities equally for hole or other
nesting birds.
- More horizontal growing branches that are more convenient
for our birds in all
aspects of
their life in a tree (nesting, perching etc.).
- More shade and combined with their more often umbrella
shape
- higher attraction rate of animals and they in return serve
as
- attraction of more insects for birds through the dung and
various animal impact.
- Familiar fruits and flowers for birds directly or they
again attract prey items for
birds.
- More chipped bark. This is living space for insects and
reptiles, also prey for birds.
- More protection with their thorns.
- Familiar browsing possibilities for mammals, once again
causing animal impact etc.
- Better vegetation on ground beneath the tree because of
better animal impact. This
vegetation
attracts birds because of food or/and nesting material.
The more chipped bark of the native trees (left) offer
better living space than the more smooth bark of the prosopis tree (right)
Native trees offer better nesting possibilities and better
and more shade for animals
Conclusion
An 82% preference of native trees by local birds means that
this percentage of birds, if not more, will be affected negatively in areas
where the prosopis tree suppresses the by 82% favored native tree.
The results of this study suggest that both the total number
and species richness of wild birds in Namibia have been reduced by the
expansion of prosopis into native vegetation.
In summary it is proven that their presence is having a
pronounced negative effect on Namibian bird biodiversity.
What can be done
First of all the cause and effect test needs to be done. To
take a decision to address the prosopis invasion situation, the cause and
effect test needs to be completed. This enables one to sort out tools, actions
and policies that oppress symptoms instead of correcting the cause.
Following the procedure of the test one asks: Do the actions
such as cutting or chopping, bulldozers scraping or dragging heavy chains,
chemical sprays, burning and root plowing really address the root cause of this
situation?
The following illustrates my point.
If you periodically bang your head against a wall, you
sooner or later will develop headache. In todays life you will say the headache
is a problem, but in the matter of fact it is a symptom caused by the banging
of your head against the wall. In todays way of living you might take some
aspirin to ease the symptom and then even stronger painkillers. In addition yet
more treatments for the side effects produced by the medicine. Or you just stop
the banging and therewith address the cause.
By asking a series of “why” questions, one finds out that
prosopis encroachment is in fact a symptom, underlying the problem (cause) of
unhealthy soil produced through overutilizing (overgrazing) with animals or/and
underutilizing (overresting) of the vegetation without animals. Both cases
(over- and underutilizing) lead to bare soil that offers good conditions for
the seeds of the prosopis trees and bushes and trees in general to germinate.
There is no competition for moisture, light and air from fibrous-rooted grass
vegetation for the tap-rooted bush or tree.
If instead attacking the symptom (effect) with poisoning,
chaining, rooting or burning out the prosopis, sooner or later the treatments
need to be repeated. Prosopis encroachment will come back until the cause
(unhealthy soil) is addressed and cured.
Simultaneously individual prosopis trees need to be removed,
preferably not chemically.
Soon the black-thorn acacia will be
To avoid prosopis
encroachment,
suppressed by the prosopis tree
proper soil management needs to be
practiced and individual prosopis trees
must
be removed
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