Department of Statistical Sciences
University of Cape Town
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Avian Demography Unit Department of Statistical Sciences University of Cape Town |
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| BIRD NUMBERS | Volume 8 Number 1, June 1999 |
6. Hosts of the Pintailed Whydah (Vidua macroura) in southern Africa
Ben M. Mines The whydahs and widowfinches (Vidua spp.) are brood-parasitic finches found across sub-Saharan Africa. The viduine finches exclusively use estrildid finches (Estrildidae) as their hosts, with each species usually parasitizing only a single estrildid finch. Such species-specificity has promoted close co- evolutionary relationships between the parasites and their hosts. The parasite nestlings are raised alongside the host young and mimic the appearance of the foster nestlings, including their complex mouth markings. Adult males mimic the songs of their specific host species, and female viduines, having also learnt the same song when raised by the foster species, seek out males singing the same host song (Friedmann 1960; Nicolai 1964; Payne 1973a,b, 1997a,b). Four species of whydah and three species of widowfinch regularly occur in southern Africa. The widowfinches use firefinches (Lagonosticta spp.) as hosts; the Paradise Whydah V. paradisaea and Broadtailed Paradise Whydah V. obtusa use Pytilia species and the Shafttailed Whydah V. regia uses the Violeteared Waxbill Uraeginthus granatinus. In contrast to the other viduines, the Pintailed Whydah V. macroura is generally regarded to parasitize a number of different hosts. For example, Roberts' notes that as well as its main host, the Common Waxbill Estrilda astrild, the Pintailed Whydah also uses Bronze Mannikin Spermestes cucullata, Orangebreasted Waxbill Amandava subflava, Redbilled Firefinch Lagonosticta senegala, Swee Waxbill E. melanotis, Neddicky Cisticola fulvicapilla and Tawnyflanked Prinia Prinia subflava as hosts. Older reports (e.g. Friedmann 1960) provide an even longer list of possible hosts. On the other hand, the Complete Book of Southern African Birds (Ginn et al. 1989) considers the Common Waxbill to be the only host and considers other records to be misidentifications or accidental. This article aims to address this confusion. Host use by the Pintailed Whydah in Africa Observations in West and East Africa now demonstrate a clearer picture of host use by the Pintailed Whydah, revealing that it generally parasitizes only waxbills of the genus Estrilda (Goodwin 1982; Payne 1985, 1997a). This includes the Common Waxbill, as well as several other Estrilda waxbills: primarily Blackrumped E. troglodytes, Orangecheeked E. melpoda, Crimsonrumped E. rhodopyga and Fawnbreasted E. paludicola Waxbills (Payne 1985, 1997a). The nestlings of these waxbills have reasonably similar mouth patterns: five spots on the upper palate and characteristic gape swellings (Goodwin 1982). The Pintailed Whydah mimics this pattern to some extent (Skead 1957) but does not exhibit the song mimicry so characteristic of the other viduines. There is some evidence to suggest that estrildid nestlings that do not exhibit the species-characteristic mouth pattern are discriminated against by the parents (Reed & Freeman 1991). This should confine the Pintailed Whydah to those Estrilda waxbills with a similar mouth pattern. A number of other estrildids have been considered as hosts, such as Swee Waxbill, Orangebreasted Waxbill and Bronze Mannikin (Friedmann 1960; Neuby-Varty 1970; MacDonald 1980; Martin 1983; Payne 1997a), yet these do not have the familiar five-spot pattern of the other hosts. Host use in southern Africa: evidence from SABAP and NERCS For southern Africa the status of hosts is unsure. Of the Estrilda hosts mentioned above, only the Common Waxbill occurs in the region. The only other Estrilda with a fairly similar mouth pattern is the Blackcheeked Waxbill E. erythronotos, but there is little overlap in range with the Pintailed Whydah. The lack of other suitable hosts suggests that the Common Waxbill is probably the major and only host of the Pintailed Whydah in southern Africa. Les Underhill and I used SABAP data to compare the similarity of all the viduine distributions with that of their hosts. As expected the parasite distributions were most similar to that of their specific hosts, and their distributions were not influenced by any other estrildid distributions. This was also true of the Pintailed Whydah and the Common Waxbill, with the parasite distribution almost identical to that of the host. This suggests that the Common Waxbill is the major host of the Pintailed Whydah in southern Africa, with other estrildids seemingly not affecting the distribution of the Pintailed Whydah. However, I noticed from ASAB2 that the Pintailed Whydah seems to be more common than its host in the area around Gauteng and eastern North West Province (extending to Rustenburg and Potchefstroom), which suggested that another host might be utilized here. I also noted that in the same area the Orangebreasted Waxbill has a particularly high density. This prompted a search of the records of the South African Nest Record Card Scheme and an investigation into the hosts used by the Pintailed Whydah in southern Africa. I located 79 records from the entire period of NERCS, from 1900 until the present day, but with the majority of records from the 1950s and 1960s. Ten species were recorded as hosts (Table 1). The Common Waxbill was by far the most numerous and represented about two-thirds of all records in southern Africa, confirming its status as the major host. While the Orangebreasted Waxbill provided about one-fifth of all records, the remaining eight species (five species of estrildid finch, two warblers and a widow) yielded only 12 records. The non-estrildid records are somewhat doubtful as viduines exclusively use estrildid finches. The prinia and cisticola records may be accounted for as eggs of the Cuckoo Finch Anomalospiza imberbis which regularly parasitizes these species. Another possibility is that some species of finch (Cutthroat Finch Amadina fasciata, Redheaded Finch A. erythrocephala and the Orangebreasted Waxbill) often use disused nests, rather than constructing their own (Goodwin 1982; Colahan 1982). The adopted nests often contain eggs of both the original owner and the usurper. The eggs of these three species could easily be misidentified as eggs of the Pintailed Whydah (all are white eggs) and could account for the widow and some of the other records. The estrildid records are probably reliable, though only records where the parasite egg or nestling can be positively identified are definitely genuine. The Redbilled Firefinch is the host of the Steelblue Widowfinch V. chalybeata, so the three records may be misidentifications of the eggs of this species. The other estrildids have very different mouth patterns to the Pintailed: for example, the Swee Waxbill has no mouth-spots on the upper mandible at all, whereas the mannikins have horseshoe-shaped bars instead of spots (Goodwin 1982). Despite the non-matching mouth patterns, these records are most likely reliable but may be examples of female whydahs mislaying in the wrong nest. Payne et al. (1993) noted that about 1% of widowfinches mimic the song of an estrildid that is not the usual host, suggesting that eggs had been mislaid but were successfully raised. It is likely that because of the low frequency of occurrence, these estrildid records are accidental records, rather than regular host use. However, the high proportion of parasitism records on the Orangebreasted Waxbill (about 20%) suggests it is a regular host in southern Africa. A further analysis of the nest records (Table 2) confirmed that, in the area of Gauteng and eastern North West Province (25º30'-27º00'S, 26º30'-30º00'E), the Orangebreasted Waxbill was the significant host, as the majority of parasitism records by the Pintailed Whydah in this region were of this species rather than the Common Waxbill. The remaining two Orangebreasted records are from Harare but the parasitism rate is low (0.5%), suggesting it is a rarely used host there. Around Harare the Common Waxbill is relatively common, so it would seem unlikely than an alternative host is required. I found 13 records of parasitism of the Orangebreasted Waxbill in Gauteng and the surrounding region (eight are from the Witwatersrand area, three from Pretoria and two records from Potchefstroom). By comparison, there were only eight records of parasitism of the Common Waxbill. In this region, the reporting rate of the Common Waxbill is relatively low (Table 3) when compared to a similar region directly to the north (24º00'-25º30'S, 26º30'-30º00'E), and to the mean reporting rate for its whole range. By comparison the reporting rate of the Orangebreasted Waxbill is relatively high in this region, being almost as high as for the Common Waxbill. The higher parasitism rate of the Common Waxbill in this area (35%) suggests that it is the preferred host, but owing to the relatively low density of the Common, the Orangebreasted, which has similar habitat preferences, is regularly used. Density would therefore appear to be a key factor in determining host use by the viduines. Where the density of the usual host is low, an alternative host, if available, may be used. The fact that the Common Waxbill is common in this area, although less so than in neighbouring areas, suggests that the use of two hosts allows a significant increase in the density of the parasite. The Orangebreasted Waxbill therefore constitutes a significant host of the Pintailed Whydah in southern Africa, in at least one area where the density of the Common Waxbill is comparatively low. This may be the first evidence for the regular use of a non-Estrilda host by the Pintailed Whydah. The mouth-pattern of the Pintailed Whydah enables it to parasitize a range of Estrilda hosts and allows it to colonize areas where its major host is not present. For example, in southern Ghana the Common Waxbill does not occur, but the Blackrumped and Orangecheeked Waxbills do, and these are used as hosts (MacDonald 1980). In southern Africa, in areas where the preferred host occurs at relatively low density, the lack of an alternative Estrilda host has meant that the whydah has colonized a host with unsuitable mouth markings. The mouth pattern of the Orangebreasted Waxbill has 16 mouth spots (Colahan 1982; Harrison 1962), which is vastly different from that of the Pintailed Whydah or its regular Estrilda hosts. It has been shown that nestlings with non- mimetic mouth markings are discriminated against when conditions are unfavourable, but when food is plentiful such nestlings can be raised successfully by foster parents. (Reed & Freeman 1991). The Orangebreasted Waxbill is parasitized in West Africa by the Goldbreast Indigobird V.˙raricola (Payne & Payne 1994) which does not have a mimetic mouth pattern. This suggests that parasitism of this species is certainly possible, even without similar gape markings. Conclusion and request for further records I suggest that in southern Africa the Common Waxbill is the primary host of the Pintailed Whydah. The Orangebreasted Waxbill is a regular secondary host in areas where the density of the Common Waxbill is comparatively low. Alternative estrildid hosts such as the Swee Waxbill and the Bronze Mannikin may also be used, but not regularly. It must be noted that the evidence for this is suggestive, based on an informal comparison of distributions of parasite and host (which may not necessarily indicate host use) and from nest records which have not necessarily been substantiated. The only certain way to establish the status of the Orangebreasted Waxbill as a significant host of the Pintailed Whydah in southern Africa is by positively identified cases of parasitism. Such confirmation would require identification of parasite nestlings rather than just foreign eggs or associations of fledgling parasites with family parties of Orangebreasted Waxbills. I therefore make a request for any confirmed records of parasitism by the Pintailed Whydah, both on the Common Waxbill and the Orangebreasted Waxbill and for any other hosts. This will help to establish the true status of host use by the Pintailed Whydah in southern Africa. Acknowledgements I thank Les Underhill for the Atlas analysis, James Harrison for access to the nest records and Bob Payne and Mike Brooke for comments. Thanks to Kgorogoro Game Reserve for accommodation in South Africa. I would like to acknowledge the support of the Natural Environment Research Council, UK. References
Colahan, B.D. 1982.
The biology of the Orangebreasted Waxbill. Ostrich 53: 1-30.
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Document posted: 26 January 2000