Black Larks use animal dung to buffer nest temperatures and avoid nest trampling by livestock
Functions of extensive animal dung “pavements” around the nests of the Black Lark (Melanocorypha yeltoniensis). Fijen, T.P.M., Kamp, J., Lameris, T.K., Pulikova, G., Urazaliev, R., Kleijn, D., & Donald, P.F. 2015. The Auk 132(4): 878-892. DOI: 10.1642/AUK-15-38.1
The addition of objects such as stones or flowers to bird nests is widespread, with bowerbirds as famous examples. A number of desert species create ramparts of stones around their nests. The use of animal dung is rare. Here we report on dung use in Black Larks, who assemble large structures around their nests. We conducted a number of field experiments to shed light on possible adaptive reasons for this behaviour.
Black Larks Melanocorypha yeltoniensis breed on the Eurasian steppes, and over 90% of their population is concentrated in Kazakhstan. Many aspects of their life remain a mystery. Why is there such a strong sexual dimorphism (unusual for a lark), with pitch black males and dull brown females? Why do males stay in the breeding areas in the bitterly cold and snowy winter (Urazaliev et al. 2012), while females wander to warmer countries in the south of Central Asia? And is the strongly skewed sex ratio (Krivitskii 2007, with perhaps 8-9 males on one female according to our data) somehow related to the divergent migration strategies? During research on the species’ breeding ecology in 2011 (Kamp et al. 2012), we stumbled upon another mystery. When searching for nests, we soon realised, that after flushing a female we would just need to look for horse and cattle dung piles at the flushing spot that looked slightly ‘arranged’. Amidst these dung ‘pavements’, we usually found the nest.
We watched females flying back to nests, carrying dung pieces in their bills. The largest pavements contained over 130 pieces of dry dung, weighing on average 3.8g (about 10% of the female’s body weight) – clearly some investment was needed to build these structures, thereby increasing exposure to predators.
This soon brought up the question what the adaptive functions of these dung pavements were. Two motivated Dutch students teamed up with two Kazakhstani counterparts and returned to the study site in 2013 to investigate. More nests were found, resulting in a total of 220 nests whose fate could be related to dung pavement size and characteristics. This allowed us to test if nests with larger pavements had a higher probability to survive, perhaps by deterring mammalian predators by smell or a camouflaging effect of the dung. Alternative hypotheses were formulated: dung could shelter the nest from cold spring winds and insulate against frozen ground, dung might attract invertebrates and thereby increase prey availability near the nest, and dung could even protect the nests from being trampled by livestock, as cattle and horses avoid to step into their own faeces.
We set out to test some of these hypotheses: data loggers were installed that recorded nest cup temperature in active nests and in a controlled experiment with artificial nests, adding varying amounts of dung. Pitfall traps were buried at nests and random locations to assess spider and beetle numbers. But how to test the idea of the dung pavements acting as ‘anti-trampling devices’? Nothing easier than that – just ask a local shepherd to lend you their cattle herd for a few days and set up a large-scale trampling experiment. An extensive grid was prepared in the steppe, and clay disks that mimicked nests and would break when stepped on were placed at 100 grid nodes in a regular manner. Half of the artificial nests were fitted with dung pavements resembling those of the Black Larks, and half were left blank without dung. The amused 92 research cattle were then driven onto this grid on six days, and remained there grazing for one hour. Afterwards, the frequency of broken artificial nests with and without dung was calculated.
While analysing the data, it became clear that the dung is unlikely to deter (or attract) hungry foxes and other mammalian predators – nest survival rates were independent of dung presence or dung pavement size. There was also no support for the hypothesis that the dung lures in larger numbers of arthropods. However, dung clearly buffered temperature extremes under controlled conditions. Large pavements increased the minimum daily temperature in the nest cup by 0.5°C, suggesting an insulating effect in cold nights. Interestingly, the maximum nest cup temperature, reached during the hottest hours of the day, was decreased on average by 1.8°C when a large pavement was present. Data logger and camera use in the field showed that females leave the nests for periods of up to three hours in the morning and afternoon, so the temperature buffering capacity of the dung might allow them to forage longer without risking the eggs and chicks to get cold or overheat, or collect more food for the nestlings. An analysis of chick growth parameters measured in the field did reveal some support for faster chick growth in nests surrounded by more dung, but a larger sample size is needed to confirm this.
In the trampling experiment, the probability of a nest being trampled was lower for those situated in dung, suggesting that dung pavements might indeed stop grazers from stepping on nests. Even more interesting, Black Larks scaled the size of the pavement to perceived trampling risk: in areas with higher levels of background dung (and therefore higher grazer density), pavements were larger. This was not a simple expression of dung availability, as at every nest enough dung was available within a radius of 8 m to build a pavement of the observed size.
The dung pavements described here resemble in function and structure the stone ramparts and pavements found in various desert species and the Horned Lark (Cannings and Threlfall 1981, Yosef and Afik 1999). Their potential to preclude livestock trampling might be an additional benefit, and they so illustrate the close functional links between large grazers and birds in the Eurasian steppe ecosystem.
References and further reading
Cannings, R. J. and W. Threlfall (1981). Horned lark breeding biology at Cape St. Mary’s, Newfoundland. The Wilson Bulletin 93:519–530. View
Kamp, J., Siderova, T.V., Salemgareev, A.R., et al. (2012) Niche separation of larks (Alaudidae) and agricultural change on the drylands of the former Soviet Union. Agriculture, Ecosystems and Environment 155:41–49. View
Krivitskii, I.A. (2007) Notes on the biology of the Black Lark Melanocorypha yeltoniensis. Selevinia 15:131–137.
Urazaliev, R.S., Iskakov, T., Kamp, J. (2012) Aggressive intraspecific behaviour among male Black Larks in winter. British Birds 105:37.
Yosef, R. and D. Afik (1999). Function of stone carpets at the nest entrance of Blackstarts Cercamela melamira. Vogelwelt 120:155–161. View
Dung piles are important requisites in Black Lark territories © Maxim Koshkin; © Johannes Kamp; © Johannes Kamp; © Thomas Lameris
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