Interspecific competition between Helmeted Guineafowl and Cape Spurfowl at Zandvlei

Nature Reserve

C.Q. Sheasby

PO Box 30028 Tokai, Greater Zandvlei Estuary Nature Reserve, Cape Town

Abstract

From 2003 to 2005 ad hoc removal of Numida meleagris (Helmeted Guineafowl) was undertaken at Zandvlei Nature Reserve, Cape Town. From 2006 to 2009 intense removal efforts were undertaken and weekly counts from 2003 to 2009 were statistically analyzed to determine whether the removal of Numida meleagris had an effect on the population of

Pternistis capensis (Cape Spurfowl). In order to establish which resources these two species could compete for, a comparison matrix was compiled indicating possible competition for food, shelter and breeding habitat. A total of 334 bird counts were analyzed. From 2003 to 2005 a mean of between 6 and 9 showed an increase in the Numida meleagris population with a low mean increase of between 4 and 4.9 Pternisitis capensis per count for the same period. In

2006 to 2009 (intense removal period), the Numida meleagris population showed a strong decrease in mean from 6 to 2.5 birds per count and capensis showed a strong mean increase of between 5.5 and 11.5 birds per count. Annual means for the entire period show a strong inversely proportional relationship between the two species indicating the alien Numida meleagris could have a long term negative effect on the populations of Pternistis capensis in the

Western Cape.

Keywords: Helmeted Guineafowl, Numida meleagris, Cape Spurfowl, Pternistis capensis, gamebird, interspecific competition, exotic gamebird control, diet comparisons

Author: C.Q. Sheasby* email: [email protected]

Address: PO Box 30028, Greater Zandvlei Estuary Nature Reserve, Cape Town

*To whom correspondence should be addressed Introduction

The Helmeted Guineafowl (Numida meleagris) is an alien species to the Western Cape and is believed to have been introduced into the winter rainfall region initially by Cecil John Rhodes

(Clancey 1967) as well as being introduced to vineyards in the Western Cape in 1939 in an attempt to control fruit weevils Phlyctinus callosus (Little et Al., 1995). Available literature states that many species of exotic game have been introduced, most of these for aesthetic or hunting reasons. Alien gamebirds pose a conservation threat as the alien populations have fewer limiting factors or can overcome these factors in their new environment. This often leads to a population explosion. 74 species of terrestrial gamebirds have been introduced of which 33 have become established. Six species have become agricultural pests or conservation concerns as they hybridize with or out-compete native species (Johnson 1978: 46-50). The Cape

Spurfowl (Pternistis capensis) is regarded as the second most important gamebird in the Cape

Province (Heyl et al., 1988).

Numida meleagris has been widely introduced but has according to Johnson caused little damage. The fact that this widely distributed bird is a domesticated weaker version of the original wild stock seems to pose more of a threat in the scientific articles (Johnson 1978: 46-

50). In the Western Cape, no literature is available on the competition between Numida meleagris and Pternistis capensis and the implications this competition presents for the future of

Pternistis capensis in the Western Cape Province.

The Greater Zandvlei Estuary Nature Reserve (GZENR) has been monitoring bird numbers

(terrestrial and waterbird) since 2001. Individual bird numbers of Numida meleagris and

Pternistis capensis during weekly bird counts undertaken from 2001 to 2009 show indications of population fluctuations between the two species. Numida meleagris populations are controlled within City of Cape Town Biodiversity Management Nature Reserves as part of the conservation mandate. In Zandvlei from 1998 to 1999, extensive trapping was undertaken to remove Numida meleagris

(Dorse, Pers. Comm., 2009). From 2000 to 2005 removal was undertaken on an ad hoc basis when time permitted. From 2006 to 2009 it became an important focus for management to determine what impact this species has on the indigenous Pternistis capensis. The bird count data from 2001 to 2003 indicate for these species presence or absence leaving the data largely numerically unreliable; however the count data from 2004 to 2009 are numerically accurate and comparable.

Habitat and biology of the two species were compared to define which resources they may compete for and bird count data were collected and analyzed to show population changes between the two species in relation to control programmes to statistically test whether Numida meleagris has a negative impact on the breeding success of Pternistis capensis based on utilization of resources during critical periods.

Methods

Study Area

The northern section of Zandvlei Nature Reserve (S 34 04’ 55.5” E 18 28’ 0.13”) situated between Muizenberg, Marina da Gama and Retreat, Western Cape was used for this study as it is the largest natural terrestrial portion of the reserve where bird counts are undertaken weekly.

The terrain is flat with few contours that extend higher than 2m ASL. The vegetation is classified as Cape Flats Dune Strandveld and areas of disturbed vegetation. The northern portion was proclaimed as a Bird Sanctuary in 1980s and consisted of 22 hectares of land. The reserve was enlarged and reproclaimed in 2006 to include the estuary water body and rehabilitated areas adjacent to it. Comparison matrix

In order to show the similarities and differences between Numida meleagris and Pternistis capensis, various sources of information on the two species was collected and collated to describe the basis for competition of natural resources.

Data and statistical methods ( = Cape Spurfowl Pternistis capensis in graphs)

The weekly bird count data from 2001 to 2009 for the two species were collated and compared to ascertain population changes in Pternistis capensis in response to removal efforts of Numida meleagris. Data from 2001 to 2002 revealed only presence or absence of the two species and were inadequate as they did not reflect numbers of birds present. Data for a total period of 334 weeks from 2003 to 2009 were analyzed. For each month a population index was calculated for each species. This index is the total number of birds recorded divided by the number of bird counts undertaken during that month. This index is used as a population estimate for the month assuming that these numbers birds are counted as a reflection of the population utilizing the area. Bias is low as the bird counts are done in the same manner, using the same method, at the same time of the day and same day of the week throughout the year. The index was then used in a line chart and linear regression lines were added to show population trend over time

(12 months). The individual years’ counts and means were first analyzed, then the years 2003 –

2005 and 2006 – 2009 analyzed respectively and finally the annual means were plotted for the entire period. The correlation coefficients for counts and means were also plotted on separate graphs for the two species to show relationships. Results

The comparison matrix (Table 1) of Numida meleagris and Pternistis capensis showed high degrees of similarity. Numida meleagris diet revolves around seasonal variations, mainly rainfall. Rainfall provides larger invertebrate populations around which both species base their reproduction as the protein intake determines the reproductive success rate. This is a trait exhibited by most francolin species (van Niekerk, 2001) as well as by Numida meleagris (Crowe

& Elbin, 1987).

The linear regression analysis for individual years (figures 1 to 7) show detailed trends for the year based on the mean number of birds of the two species seen.

In 2003 the Pternistis capensis population mean was between 3.7 and 5 birds per month increasing where the Numida meleagris population mean was between 6 and 4.8 birds per month decreasing (Figure 1).

In 2004 both species showed increasing population mean trends with Numida meleagris between 8 and 10 birds per month and Pternistis capensis between 4.7 and 5.7 birds per month

(Figure 2).

In 2005 the Numida meleagris population showed a negative (decreasing) trend with bird means per month between 11 and 6 birds per month. The Pternistis capensis population means per month showed a slight decreasing trend between 4.9 and 4.8 birds per month (Figure 3).

In 2006 the negative Numida meleagris trend continued with bird means per month between 9 and 5 birds per month. The Pternistis capensis population means per month showed a slight increasing trend between 4.8 and 5 birds per month (Figure 4).

In 2007 the Numida meleagris population trend showed low numbers (means) of birds per month between 2.5 and 1 bird per month compared with a decreasing trend of Pternistis capensis between 10.5 birds and 6 birds per month, much higher than the previous means

(Figure 5).

In 2008 the low means of Numida meleagris continued to decrease slightly from between 2.5 and 1 bird (same as previous year) but the Pternistis capensis population although also decreasing, ranged between 15.5 and 7 mean birds per month (Figure 6).

In 2009 the Numida meleagris numbers were higher due to breeding success but removal forced a decreasing trend from between 14.5 and 0 birds per month. The Pternistis capensis population showed higher mean numbers but also a decreasing trend of between 11 and 9 birds per month, the highest range of Pternistis capensis means from 2003 to 2009 (Figure 7).

It was calculated that from 2003 to 2005 the Numida meleagris population was readily increasing from a mean of 6 birds per count to a mean of 9 birds per count and the Pternistic capensis population trend was much straighter with a mean of 4 to 4.9 birds over the 3 year period (Figure 8). From 2006 to 2009 however, the population trend changed dramatically in both species due to the removal of Numida meleagris. The population trend for Numida meleagris started at a mean of 6 birds at the beginning of 2006 but dropped to a mean of 2.5 birds by September 2009 (Figure 9). The population of Pternistis capensis took advantage of this and the trend shows a strong positive correlation to removal of Numida meleagris with the population mean starting at 5.5 birds and increasing to 11.5 mean Pternistis capensis during the period. This is further supported by the figures showing the correlation between Numida meleagris and Pternistis capensis that for the means and the counts of 2003 to 2005 (Figure 11 and 13), the Pternistis capensis population sat between 3 and 7 birds(means) and 4 and 7.5 birds (counts) respectively but between 2006 and 2009 (Figure 12 and 14) the population sat between 8 and 9 birds (means) and 9 and 11 birds (counts) respectively showing a large population increase after intense removal of Numida meleagris had commenced. The population means plotted on Figure 10 clearly indicates the inversely proportional relationship between the population size of Numida meleagris and that of Pternistis capensis, the latter decreasing as a result of pressure and competition from an increasing population of

Numida meleagris and increasing when the population of Numida meleagris decreases.

The statistical findings from 2003 to 2009 are located in Table 2 and 3 for Numida meleagris and Pternistis capensis respectively. These further support the hypothesis that the Numida meleagris population had an impact on the Pternistis capensis population and the population mean fell between 3.45 birds and 4.82 birds prior to removal of Numida meleagris, but increased to between 7.56 and 9.66 birds after removal had been sustained from 2006 to 2009.

The removal of Numida meleagris between 2006 and 2009 removed close to 100 birds from the area including 13 from Westlake Wetlands. This had an impact on the population bringing it down to 7 birds in 2008. These birds were able to breed successfully during that season, but further removal efforts brought this down to 3 birds in late 2008.

Figure 15 shows the predicted growth and trend pattern of Pternistis capensis at the population indicated by counts of Numida meleagris for the period 2003 to 2006. Although the population is still expanding (and does not account for natural predation), the population growth range is from

(and) between 4 and 7.5 birds. Figure 16 uses the count data of Numida meleagris from 2006 to

2009 to predict the population growth of Pternistis capensis and shows that the range was between 8 and 12 birds, almost double that of the previous time period when removal of Numida meleagris was not an intense management practice.

Discussion

The removal of natural vegetation and changes to the environments over vast tracts of land has led to a decline in many species of including birds. While some birds have been able to adapt to these changes and thrive, others have fared poorly and are now further restricted in range due to habitat fragmentation. Pternistis capensis already confined to the Cape Floristic Region is found in the coastal and coastal areas is already under pressure.

In 1988, Heyl et. Al. had already stated that the range of Pternistis capensis had decreased and the bird numbers in the populations had declined. Since 1988 severe land transformations have taken place and the range and population of Pternistis capensis is now more than likely even more vulnerable.

Bothma (2006) reported that many heated arguments have raged over the introduction of exotic wildlife and its possible effects on indigenous species. He claimed that short term economic gain was the reason for many introductions and due to the short time span of man, we do not see the long term effects that these species can have. The Rule of Gauss says that two species with similar life histories and characteristics cannot occupy the same land and habitat indefinitely without the one causing the decline of the other. Most times it is the indigenous species that is out-competed.

Johnson (1987) explained the ecological problem that the domesticated Numida meleagris now poses to the wild stock which differs to a large extent, however no mention of it being a competitor to indigenous game birds was mentioned, only that the domesticated version is weaker in some cases and the fact that it is a poor parent is the cause for this bird not being classed in that time as a conservation threat. This may have been prior to the indication that it could become a serious competitor and threat to the indigenous Pternistis capensis. Wolf &

Milstein (1987) stated that alien species often adapt to new surroundings quickly and have a range of tolerance to adverse conditions which may make it better at surviving than indigenous species, especially if it has been changed by manmade or artificial interventions. Reference to the domesticated versions of Numida meleagris was again made by Wolf & Milstein (1987) but no reference was made to the potential threat these birds have on indigenous game birds.

Little et. Al., (1995) reported that Numida meleagris studies in the fruit farms showed it having a large impact on the total number and diversity of invertebrates available through direct consumption or changes in the vegetation. Between 5 and 38 % of the food eaten by Numida meleagris on these farms consisted of invertebrate matter. These “farm birds” were reported to exhibit the same feeding patterns as wild Numida meleagris and changing from a vegetable dominant diet in the non breeding season to an invertebrate dominant diet leading up to and during the breeding season. This would no doubt impact the amount of invertebrates available to Pternistis capensis.

Removal efforts of Numida meleagris of approximately 100 birds from 2006 to 2009 had positive effects on the populations of Pternistis capensis. During the period 2003 to 2005 the removal of

Numida meleagris was an ad hoc management practice which was only undertaken when large numbers of Numida meleagris were seen. From 2006 to 2009 the intense removal showed an increasing trend of the Pternistis capensis population and a higher prediction of growth in the future if this practice is continued.

Artificial breeding of Pternistis capensis has showed low rates of survival (22.3%) and low egg fertility (57.7%) even though wild birds were used to stock breeding cages. Low survival rates were attributed to close proximity of birds causing stress and the spread of diseases in chicks, however released birds bred died within six months attributed to possible high competition with other birds indicating a high mortality rate in this species under stressful environs (Heyl. Et al.,

1988).

Conclusions

From these data, it shows that Numida meleagris numbers have a definite negative impact on the populations of Pternistis capensis and competition between the two species for similar resources exists. Conservation of this indigenous species can be improved by removal of

Numida meleagris by all land owners and management authorities and trap success is high.

The species should be classified in the Western Cape as a listed invader and control methods should be enforced. As Numida meleagris move around and tend to set up flocks around areas that have sufficient watering holes, a province wide control programme is necessary to ensure that this species impact on the indigenous Pternistis capensis is kept to a minimum. If this is encouraged and enforced, a difference in numbers could be visible in 3 to 5 years as was the case with this study.

In order to ensure that the species does not bounce back, the control efforts need to be sustained and the population pushed past its threshold of predation so that the numbers will remain low and cannot reach the levels they were at previously.

Due to the fact that in urban areas few predators exist in this scenario, the control efforts would have to be maintained to mimic this. The numbers of birds should be counted regularly to ascertain if the Pternistis capensis populations in other areas re-establish themselves as they did at Zandvlei or if they are facing other competitive forces.

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Table 1: Comparison matrix of Numida meleagris (Helmeted Guineafowl) and Pternistis capensis (Cape Spurfowl)

Comparison Numida meleagris Pternistis capensis

Matrix Helmeted Guineafowl Cape Spurfowl

Insects in summer (protein)

Insects in summer (protein) Vegetable matter most of the other Food and seasons but also includes various Vegetable matter most of the other nutrition invertebrates (Clancey, 1967 & Little et. seasons (Clancey, 1967)

Al, 1995)

More extensive than Cape Spurfowl due Restricted to Cape Floristic Region Distribution to translocations for hunting purposes (Clancey, 1967) 1800s

Monogomous, breed on ground in Monogomous, breed on ground in dense scrub dense scrub

Breeding needs Sept – Dec Aug – Nov and biology (Liversidge, 1987; Crowe & Elbin, 1987)) (Liversidge, 1987 & van Niekerk, 2001)

Clutch size: between 6-8 and 26-38 eggs Clutch size: 6 -14 eggs (Clancey, 1967) (Clancey, 1967)

786 young produced in breeding year 74 young produced in a breeding year Success of species Can breed all year round in good (Liversidge, 1987) conditions (Liversidge, 1987) Table 2: Statistical findings of Numida meleagris counts 2003 to 2009

2003 2004 2005 2006 2007 2008 2009

Mean 5.2 9.11 8.46 7.3 2.1 1.84 4.58

Guineafowl N=51 N=51 N=45 N=47 N=52 N=50 N=39

Numida meleagris

Standard 9.8481533 7.8279534 9.4612506 2.9890462 2.9759559 7.5956341

Deviation 6.9611458

Variance 48.457551 96.986122 61.276855 89.515264 8.586727 8.8563135 57.693657

Range 0-31 0-31 0-26 0-38 0-12 0-11 0-20

Dispersal 9.022281 10.638781 index

Standard 0.707961248 0.479978323

Error

95% 6.56 and 3.45 birds confidence 9.33 birds and 4.82 interval birds

Table 3: Statistical findings of Pternistis capensis counts 2003 to 2009

Mean 4.34 4.77 4.5 4.8 8.34 10.8 7.49

Spurfowl n=51 N=51 N=45 N=47 N=52 N=50 N=39

Pternistis capensis

Standard 3.418139 4.923911 4.098321 4.754568 7.877838 8.22868 6.744118

Deviation

Variance 11.68367 24.2449 16.79623 22.60592 62.06033 67.71118 45.48313

RAnge 0-15 0-25 0-17 0-24 0-28 0-35 0-27

Dispersal 3.58044 6.336006 index

Standard 0.34908354 0.534341467

Error

95 % 3.93 birds 7.56 birds and 5.81 and 9.66 confidence birds birds interval

Figure 1: 2003 Population indices plotted as mean number of birds per month

Figure 2: 2004 Population indices plotted as mean number of birds per month

Figure 3: 2005 Population indices plotted as mean number of birds per month

Figure 4: 2006 Population indices plotted as mean number of birds per month

Figure 5: 2007 Population indices plotted as mean number of birds per month

Figure 6: 2008 Population indices plotted as mean number of birds per month

Figure 7: 2009 Population indices plotted as mean number of birds per month

Figure 8: Linear trend of the two species 2003 to 2005 (before intense culling)

Figure 9: Linear trend of two species 2006 to 2009 (after start of intense culling)

Figure 10: Linear trend of two species over entire period (2003 to 2009) showing inverse relationship between two species

Figure 11: Guineafowl to Spurfowl correlation 2003 to 2005 (based on mean birds per month)

Figure 12: Guineafowl to Spurfowl correlation 2006 to 2009 (based on mean birds per month)

Figure 13: Guineafowl to Spurfowl correlation 2003 to 2005 (based on counts of birds)

Figure 14: Guineafowl to Spurfowl correlation 2006 to 2009 (based on counts of birds)

Figure 15: Prediction of Spurfowl population growth based on Guineafowl population size 2003 to 2005

Figure 16: Prediction of Spurfowl population size based on Guineafowl population size 2006 to 2009