Sunday 5 January 2014

175 | THE IMPACT OF PROSOPIS TREES ON NAMIBIAN BIRD LIFE




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.

Prosopis history

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.


Prosopis tree survival tactics

- 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


  meters in all directions.
- 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
-------------------------------------------------------------------------------------------------------

Sociable Weaver                            20
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)
------------
-------------------------------------------------------------------------------------------------------



Table No. 2
-------------------------------------------------------------------------------------------------------
Location of site: Brent Carlsson Road, Windhoek
















Date of observation: 1st February 2013
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