Eagle breeding fails

ALTHOUGH the Klipriviersberg Verreaux’s eagle pair were observed refurbishing their nest a few months ago and the female laid two eggs in it, no live baby eagles have been forthcoming.

Odette Campbell (member of Klipriviersberg Verreaux’s Eagles, incorporating Wits Bird Club) noted that the eagles’ first visit to the nest was on February 23 this year. Three days later the first observations of nest refurbishment were recorded by Les Morris (member of Klipriviersberg Verreaux’s Eagles, incorporating Wits Bird Club) on February 26.

By March 1, large sticks were being delivered to the nest by both eagles. Nest refurbishment and the delivery of leafy green sprays to line the nest cup was made by both eagles during the entire month of March, stretching into the first week of April. On April 6 Les observed that Khetiwe (the female eagle) had laid her first egg; her second egg was presumably laid four days later on April 10.

“This is quite early in the season, if we compare to the eagles’ other cousins, namely the Wonderboom (Pretoria) eagle pair that laid their clutch on April 25 and 29 and the Roodekrans (Roodepoort) pair, which laid during the second week of May. The latest recording of laying by the Klipriviersberg pair was during 2008 in mid-June, which is indicative that laying dates may vary considerably,” said Les and Odette.

Project members were invited to take part in a session to provide their opinions pertaining to the failed breeding attempt and, interestingly, a varied response was received. The adverse weather conditions were blamed, as heavy thunderstorms with lightning, hail and torrential rain were recorded on April 6, 7, 11 and 13, precisely during egg-laying and the early incubation period. There was also frequent crow harassment, with the eagles being relentlessly plagued and dive-bombed, some days by as many as 23 birds – forcing the eagles to retaliate and leave the nest exposed for 20 minutes or more, which is unacceptable.

Another reason given for the failed breeding attempt was the decline (compared to previous years) in the eagles’ natural prey – which is mostly dassies and to a lesser extent guinea fowl. This results in prey stress, making the eagles incapable of hunting frequently and successfully. Also recorded is that dassies are feeding nearer to residential homes, making them more difficult to hunt successfully. Increased bush density may also have contributed to reduced prey prevalence; temperature and drought during the preceding years of 2015/2016 may have resulted in diminished prey availability. However, the rainfall recorded during the 2016/2017 season was excessive and especially extraordinary during April. Inclement weather patterns impact upon prey and scavengers and a change in their behaviour will impact upon the eagles’ ability to adapt. The question remains: Are the eagles adapting fast enough to adapt to the change in weather patterns?

Also, the possibility exists that only one egg may have been laid (as has previously been recorded elsewhere) and that this egg may have addled; human disturbance and aircraft flying lower than usual may also have caused the eagles stress during the crucial incubation period. Stress could have impacted negatively on the pair, causing the breeding attempt to fail. Of paramount importance would be to retrieve the egg(s) from the nest immediately after the eagles have aborted incubation and to have the eggs sent to the Onderstepoort Veterinary Institute for analysis to determine when the embryos died and/or what caused the eggs to addle. This information will further assist the project members to be more vigilant in their protection of the eagles during their ultra-sensitive incubation period and to reduce disturbances to the absolute minimum.

“We remain hopeful yet that the eagle pair will contemplate a second breeding attempt this season, which is not abnormal and as there is some time yet, they may just surprise us all,” said Bo van der Lecq, Project Manager, Klipriviersberg Verreaux’s Eagles (including WBC).

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