Construction and thermal insulation of Ethiopian Bush-crow nests

The main function of bird nests is to provide shelter for eggs and nestlings in order to support optimal offspring development. While this basic condition applies to all nests, an enormous constructional variety in nests has evolved. Regarding its thermal properties, the avian nest construction generally represents a compromise between heat conservation,heat dissipation, and protection from external heat.

The Ethiopian Bush-crow is an endemic Ethiopian bird species which has a very small and climatically distinct range that is cooler, dryer and more seasonal than the surrounding areas. Bush-crows build large domed nests made of thorny twigs with comparatively thick walls and a soil-lined bottom. In a preliminary study* we studied the thermal properties of a bush-crow nest with the aid of IR thermography. Our results show that there was no heat emission in the early morning and that nest surface temperatures clearly corresponded to the temperature changes during the day. Therefore we hypothesise that the nest construction provides substantial thermal insulation during the night time and presumably also delays temperature increase in the internal nesting chamber during the day time. We suggest that the bush-crow’s specific nest construction may have contributed to its persistence in the climatically unique south Ethiopian conditions.

* Töpfer, T. & K. Gedeon 2012: The construction and thermal insulation of Ethiopian Bush-crow (Zavattariornis stresemanni) nests: a prelimary study. Avian Biology Research 5 (4): 198-202.

Thermographic image of a bush-crow nest just before sunrise (a) and at noon (b).

Why share Ethiopian Bush-crow and White-tailed Swallow an identical range in spite of a very different history of colonization?

Distribution map of the three Hirundo species

There are two endemic bird species in southern Ethiopia which live in almost an identical range: Ethiopian Bush-crow and White-tailed Swallow. But apparently their respective ancestors come from very different parts of the world. The closet relatives of Zavattariornis - ground jays of the Genus Podoces - live in Central Asia, whereas the relatives of Hirundo megaensis are all from Africa. Dor et al (2010) describe the relationship of the swallows as follow:

"...the ‘Pearl-breasted Swallow’ clade, is comprised of the Pearl-breasted (Hirundo dimidiata), White-tailed (H. megaensis) and Pied-winged swallows (H. leucosoma). ... Phylogenetic relationships of the White-tailed Swallow, a species endemic to a small region in southern Ethiopia, have not been previously examined, but based on plumage traits it was expected to be close to the Pearl-breasted Swallow  (Sibley and Monroe, 1990; Turner and Rose, 1989), and our analysis confirmed this affinity. Indeed, the genetic divergence between H. megaensis and H. dimidiata (0.7%) is by far the smallest existing among species in the genus (otherwise, range = 2.0–11.6%) and is equivalent to the divergence among populations of the polytypic H. rustica (range 0.25–1.6%). H. megaensis and H. dimidiata inhabit similar habitats, but are separated by a range disjunction of about 1,500 km..."

It remains one interesting question: Why share Zavattariornis stresemanni and Hirundo megaensis a nearly identical tiny range in spite of a very different history of colonization?

Masked Lark records 2011 in southern Ethiopia

Singing Bush-lark (Miafra cantillans) in Sarrite, Southern Ethiopa 

According to Ash et al. (2009) there have been only 5 Masked Lark Spizocorys personata records (altogether 18 birds) in Ethiopia in more than 110 years. In Kenya only 3 sites are known. That's worldwide only 9 known locations with four subspecies. The range is said to be 73,300 km², but probably much smaller and fragmented. Nevertheless, the BirdLife model map shows a nearly coherent and widespread distribution, which does probably not exist in this way. There is a need for research, not least because the future outlook for this species seems to be very critical due to climate change.

In southern Ethiopia the subspecies Spizocorys personata yavelloensis has been scientifically described around 70 years ago. Since then apparently no other reliable data exist on the presence of this subspecies near the place of origin.  A search in June 2011 provided, however, positive results. An encouraging large number of Masked Larks were found in an area about 80 km west of Yabello. The area is also habitat for Grevy's Zebras and intended to be part of a prospective National Park. The most common lark in the area, however, is the Singing Bush-lark (figure).

Avifauna of Ethiopia: A new approach in conservation

Harenna Forest (Bale Mountains, Oromia Regional State)

In Ethiopia, there are currently seven national parks, wildlife sanctuaries as well as several other protected areas. The conservation status is unsatisfactory in most of these sites. There are several reasons, but one of the challenges is without question the tremendous population pressure. For example, large parts of the Harenna Forest (Bale National Park) is used today by settlers. The decline in dense forests 1973-2000 was 15% between 1973 and 2000. About 4% of the forest disappeared completely (Pinard et al, no date).  After restrictive protection measures and bans have failed in recent years, one focuses on a more collaborative approach that incorporates the interests and knowledge of the local population.

This corresponds in principle to the efforts of IUCN to establish so-called "Indigenous and community Conserved Areas" (ICCA) - a so far unconventional reserve category (Kothari 2009). It remains to be seen whether and to what extent this concept is successful. For the Borana territory in southern Ethiopia Bassi and Tache (2011) have demonstrated the possibilities, but also the limitations of such an approach. Practical obstacles existed, especially in the massive immigration of settlers from other areas, political marginalization of pastoralists, and a de facto privatization of formerly communal land.

The range of the Ethiopian Bush-crow in southern Ethiopia

Ethiopian Bush-Crow (Zavattariornis stresemanni)

In July 2010 we made a survey on the endemic Ethiopian Bush-crow Zavattariornis stresemanni in southern Ethiopia (Oromia Regional State, Borana zone). Along a 2,500 km-long track about 500 GPS-based records on birds and nest sites were collected. We counted a total of 2,600 birds or nests. Previous studies on the range of the Ethiopian Bush-crow were largely limited to countings along the paved roads and on random observations. With the data now available, it is possible to estimate the range of the species more reliably. We found birds or nests in 81 grids (5x5 minutes fields). This corresponds to an area of ​​approximately 7,000 sq. km. Thus, the range of the species is larger than thought. Previous estimates were 4,600 sq. km (BirdLife International species factsheed, July 2011). The results can be found in the following maps.

Map of the track and records
Distribution map (grid map, with a grid size of 5 minutes)
Map of the main breeding areas
Density map 

We are currently working on a model that explains the limited range of the species based on data on climate and vegetation. A publication is being prepared. I am grateful to Deutsche Ornithologen-Gesellschaft (DO-G) and Gesellschaft für Tropenornithologie (GTO) for funding.