Nesting and Boat Disturbance Studies of Colonial Birds in the Okavango Delta, Botswana

Colonial waterbirds nesting at the Okavango Delta have been subjected to different forms of human disturbances. Motor boat disturbance is one main example of these disturbances. The objectives of my study were to: (I) obtain baseline data on the nesting success and nest height in colonial waterbirds of the Okavango Delta, (2) evaluate the reaction of nesting target species to motor boat disturbance, and (3) evaluate nesting success in relation to vulnerability to boat disturbance and nest height. The study occured in the Moremi Wildlife Reserve (Okavango Delta), Botswana. The study objectives relate to the following target species: African Spoonbill (Plata/ea alba), reed cormorant (Phalacrocorax africanus), purple heron (Ardea purpurea), darter (Anhinga melanogaster), marabou stork (Leptoptilos crumeniferus), and yellow-billed stork (Mycteria ibis). The target species were monitored between July 1993 and March 1994. Yellow-billed storks had the largest mean nest height of 3 .98 m (n = 20) followed by marabou storks (3 . 8 1 m,n=46) and African spoonbills (3 .05 m, n = 40). Reed cormorants had the lowest mean nest height of 1 . 74 m (n = 67), followed by purple herons and darters at 2. 1 7 m (n = 3 5) and 2.74 m (n = 1 0) respectively. The number of eggs and nestlings were recorded during each nest visit. I used a modified Mayfield method (Mayfield 1 975, Johnson 1 979) for estimating survival of nests. The following nest survival rates were determined for the target species: African spoonbills= 0.69%, reed connorants = 1.65%, purple herons= 16.71%, darters= 32.86%, marabou storks= 35.47%, and yellow-billed storks= 6 0.84%. Nest height was not positively associated with nest survival within the target species. However, nest height was positively associated with nest survival across the target species (R2 = 87.53%; Pearson correlation). The high positive correlation between mean nest height and overall nest survival of target species indicated that mortality was higher in nests located at a lower stratum in multi-species colonies. In hatched clutches, nest survival was positively associated with number of eggs hatching in African spoonbills, reed connorants, purple herons, and darters according to logistic regression (SAS 1989a). Experiments with motor boat disturbance were conducted with respect to purple herons, marabou storks and yellow-billed storks. The mean flush rate for birds (3 species combined) without boat disturbance (254 birds /30 min) was significantly lower than flush rates (23,536 birds /30 min) (P< 0.05) with boat disturbance. Purple herons (749.44; P < 0.0001) were more vulnerable to boat disturbance than marabou storks (363.08; P < 0.0001) and yellow-billed storks (0.68; P = 0.7 11) according to standardized disturbance flush rates (flushes/30 min with boat disturbance were divided by reference flushes/30 min without boat disturbance). Continued monitoring of colonial waterbirds in the Okavango Delta is recommended because of their vulnerability to human disturbance.

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Thesis - University Access Only

Discipline thesis:degree_discipline

Wildlife and Fisheries Science

Year

1996

Author dc:creator

• Motalaote, Seteng

Contributors dc:contributor

• Lester D. Flake

• Natural Resources and Conservation

Statement dc:rights

• Copyright © 1996 Seteng Motalaote All rights reserved.

Language dc:language

en

Repository record dc:identifier

https://openprairie.sdstate.edu/etd/553

OAI identifier oai:identifier

oai:openprairie.sdstate.edu:etd-1553