Birds’ nests have evolved into many shapes and sizes, but they all function to provide a secure substrate for eggs and hatchlings, camouflage and defence from predators, as well as protect the eggs, hatchlings and incubating parent from harsh climatic conditions. My doctoral studies focused on understanding the factors influencing the structure and insulation of avian nests and hence the manner in which a nest may influence the energetic cost of incubation.
FACTORS INFLUENCING NEST SIZE AND SHAPE
Comparing the size and shape of nests of 36 Australian passerine species against parent mass reveals that nest surface area increases in direct proportion to the size of the parent. Nest diameter and height increase with parent mass but as nests become larger in line with increases in parent mass, the nest cup also becomes shallower and the opening becomes wider than expected, which allows for the space that the chicks will occupy.
Nest mass increases with parent mass at a rate that matches that of a supporting structure, suggesting that structural considerations of nest construction are of primary importance to nest design. The requirement for structural support is also evident for nest thickness, which increases more than proportionally expected as parent size increases. Structurally adequate nests become thicker than expected for their size in larger birds.
Of interest is how the size or number of eggs in a clutch relates to the size of a nest. The clutch surface area and the internal surface area of the nest increase simultaneously; and the clutch volume and volume of the nest cup are also associated. Since nest design for the majority of birds in the study is in part influenced by the male and egg shape is controlled by muscles in the pelvis of the female, it is likely that one does not control the other. However, nest and egg size/shape are influenced by body size and ancestry. Therefore, it is likely that the nest and clutch are in fact independent, yet matched secondarily due to the shared influence of body mass and genetic ancestry.
FACTORS INFLUENCING NEST INSULATION
As we know, the nest surface area increases in proportion to bird size, however nests become much thicker than expected as bird size increases. The thick walls provide structural support for the parent and clutch, with the consequence that structurally adequate nests achieve greater insulation than expected, as they increase in size. Nests are often viewed as objects that are designed to prevent heat loss from the clutch and incubating parent; however the requirement for adequate structural support is the primary selective influence on nest construction, not the requirement for insulation.
By assessing the insulation of Spiny-cheeked Honeyeater (Acanthagenys rufogularis) and Yellow-throated Miner (Manorina flavigula) nests under varying wind conditions, I found that wind enters the nest material and dissipates heat, resulting in a decrease in thermal insulation with greater wind speeds. The consequence of increased wind currents around and through the nests would be a near-doubling in heat production required by the parent when incubating.
While ambient temperature does not influence the structure of nests in my study, it does influence the insulation of nests and the thermal efficiency of the material. However, temperature and precipitation (henceforth referred to as climate) act in combination, indicating that the response of Australian passerines to one variable depends upon the level of the other.
In sites with low temperatures, nest insulation may be important to maintain an appropriate microclimate for offspring and therefore birds construct nests with good insulation, irrespective of the rainfall at the site. For nests constructed in warm climates but at the two extremes of rainfall, there is a pronounced decrease in insulation for nests built in areas with high rainfall, compared to areas with low rainfall.
The effect of climate extends to the thermal efficiency of the nest materials, indicating that not only the ambient temperature, but also the precipitation of the breeding site, influences material selection during the nest construction phase. Birds breeding in warm and wet climates construct their nests with materials that have a poor thermal efficiency compared to those in dry climates. The warm temperatures may cause a relaxation in the need for insulation, and poorly insulating materials (such as sticks and grasses, rather than fur and wool) are possibly less absorptive and able to dry out faster following a rain event, to restore the insulating function of the nest.
To determine the effect of water (from rain, dew or absorption from the nest substrate) on the heat loss from the nest, I measured Tawny-crowned Honeyeater (Gliciphila melanops) nests under varying water content levels (from dry to saturated). Water penetrating the nesting material increases conductance of G. melanops nests by up to two and a half times the rate seen in a dry nest – a consequence of the decreased thermal efficiency of materials in a wet nest. As a result, additional energy is required by the incubating parent to keep clutches warm when nests become wet. Individuals should be capable of obtaining additional floral resources to deal with an energy deficit in cold and wet conditions. However, if floral resources are poor and an individual is unable to meet such energy demands, it may abandon the nest altogether.
My studies highlight the importance of nest design and construction for the thermal properties of nests – small variations in nest design can have significant impacts on the insulation value of a nest, which will in turn influence the energetic cost of incubation. The effect of rain and wind on nest insulation, and the consequence of this for the energetics of the incubating parent, reinforces the view that appropriate nest site selection that provides additional shelter is crucial for avian reproductive success.
A Variegated Fairy-wren (Malurus lamberti) was snapped in a compromising position at the Land for Wildlife office. A group consisting of one male, a female and many juveniles (being a highly sociable species, this group structure is quite common) were seen fluttering about in a Witchetty Bush (Acacia kempeana) and Old Man Saltbush (Atriplex nummularia subsp. nummularia) in search of a drink and bath. Hot tip: The juveniles are characterised by a pink-orange eye ring. Within moments of the birdbath getting topped up, the family made a rushed and chattering B-line to the water source. The male, however, managed to stay clear of the camera (see the December Newsletter for an image of the male at the Water Stabilisation Ponds). You can head to our YouTube channel to see the video of a juvenile making a splash and below for the snapshots.
See the Back Roads episode from Hermannsburg to see the Ntaria Junior Rangers at Palm Valley. LFW was there but missed the cut (we are in the background being semi-famous though). Great to support such a great ranger team! Head to ABC iView and *View the Episode.
Birdlife Central Australia ran a summer Shorebirds count at the Alice Springs PowerWater stabilisation ponds on the weekend. The surveys are a part of the Shorebirds 2020 program, which aims to raise awareness about how incredible shorebirds are by engaging the community to participate in gathering the information required to conserve shorebirds, by conducting national shorebird population monitoring at over 150 key sites around Australia. You can follow Birdlife Central Australia on Facebook to see what other birds they find around Alice Springs.
Barb Gilfedder, who was organising the event, states that the Bar-tailed Godwit (Limosa lapponica) was the most significant bird seen on the day, with the Grey Teal (Anas gracilis) coming out on top as most common (500!) and runner up of White-headed Stilt (Himantopus leucocephalus; marked on the graph under the previous name of Black-winged Stilt, Himantopus himantopus).
My personal favourite was a toss-up between the Red-necked Avocets (Recurvirostra novaehollandiae) that were swooping overhead, and the Variegated Fairy-wren (Malurus lamberti), which is of course not a shorebird but is utterly delightful. Plus, there were a couple of visiting reptiles, such as the Long-nosed Dragon (Gowidon longirostris)… not a bird at all!
As coordinator of Land for Wildlife, which is hosted by Low Ecological Services P/L, I am fortunate to enjoy visits to the PowerWater stabilisation ponds on a somewhat regular basis to conduct water testing. It’s difficult to stay focused on the task at hand when there is such an amazing array of birds around. A few chicks have been making their way into the world of late (see last month’s Bird Breeding Bonanza post and the October/November newsletter).
Birdlife Central Australia has also helped me to identify some of the more common species that I have noticed around the ponds, including the Wood Sandpiper (Tringa glareola) and the Common Sandpiper (Actitis hypoleucos). A large Wedge-tailed Eagle (Aquila audax) is sometimes seen at the ponds (see the video), along with many Whistling Kites (Haliastur sphenurus). If you want to visit the ponds for birdwatching, see the PowerWater factsheet for more information.
Batchelor Institute Alice Springs camera trapping session in November 2016 shows a cat going into a trap for a feed and a couple of inquisitive crows.
Wedge-tailed Eagle (Aquila audax) seen feeding on some kill at the Alice Springs wastewater treatment ponds.
Many avian species are breeding in town at the moment, with young chicks and fledglings making their way out into the world. Several Masked Lapwing (Vanellus miles) chicks and Black Swan (Cygnus atratus) cygnets have been seen at the Alice Springs sewerage treatment ponds over the last couple of months.
In my own yard, I have had a pair of young Magpie-lark (Grallina cyanoleuca) that recently fledged their sturdy mud nest and the family of four have been busy catching tasty insects in the lawn ever since. There is also a diligent Crested Pigeon (Ocyphaps lophotes) sitting on a nest with its chicks and other young nearby – who look rather gangly and awkward but delightful none the less! The White-plumed Honeyeaters (Lichenostomus penicillatus) reported in the last newsletter are still hanging around and are now just as vocal as their parents, though no doubt they will eventually go off to find their own territory.
What have you got breeding in your area? Send your photos in to share with the members!
By John Tyne
On September 28th, eight volunteers assisted Parks and Wildlife to conduct a census of introduced Rainbow Lorikeets in Alice Springs. The volunteers came from a number of organizations including Birdlife Central Australia, Alice Springs Field Naturalist Club and Land for Wildlife. Thirty nine locations were surveyed for rainbow lorikeets, with volunteers recording the times, location and number of birds seen and heard at each survey point. Despite the damp conditions many birds were out and about. After reviewing the data, I would conservatively estimate that there are at least 17 individual birds. The main population of birds appears to be focused in the Gillen area near the local primary school, which then probably disperses throughout Alice Springs during the day to feed. What is especially concerning is that two nesting hollows in the Todd River and a third in town are currently being used which may indicate an imminent increase in bird numbers. I would like to thank everyone very much for their help with this survey, and please keep the sightings coming in! They can be submitted to the NT Wildwatch website (http://root.ala.org.au/bdrs-core/nt-dlrm/home.htm), E-bird (http://ebird.org/content/ebird/) or submitted to me directly (John Tyne, John.Tyne@nt.gov.au ).
~ John Tyne, Parks and Wildlife NT
By John Tyne, Wildlife Ranger, Parks and Wildlife Commission of the NT
Over the last six months I’ve been monitoring the feral Rainbow Lorikeet population around Alice Springs. Most of these Lorikeets are likely to have escaped or been released from aviaries over the years, but recently they have been spotted nesting in hollows around town. I’ve got a decent handle on where they are now, but it’s been difficult to determine how many there are. I’m putting together a group of volunteers to help conduct a census to get an estimate on how many of the birds are out there. If any Land for Wildlife or Garden for Wildlife members are interested, please get in touch via email (John.Tyne@nt.gov.au) by Sunday the 25th of September to express interest. The time and date for the survey will be from 6:30-8am Wednesday the 28th of September.
Once I have participant numbers, I will print up a map with locations for the individuals to take observation from. I’m planning on meeting at 6:15 am, at the Town Council carpark to distribute the maps, pencils, etc. From the observation locations, I’ll ask that people listen and look for the lorikeets. If they are seen, the observer will need to record the time and a count of individual birds. If they are heard, they can try to move to where they can be seen, then take the time, a count, and record the new location. If the birds are moving, they can draw a line on the map indicating the direction of travel. When an observation is made, or you don’t hear or see anything after 10 minutes, participants can move on to the next location. At 8 am we can all meet back at the Town Council carpark, and I can collect the maps and observations.
There is no control work planned for the birds at the moment. This survey is really just a baseline so I can gather some data on how many birds are out there. If no control work is undertaken, it will be useful to see if there is any change in the population. If there is control work undertaken, it will help to determine if or how successful the work is.
Get in touch if you are willing to assist with the survey!
~ John Tyne
Garden for Wildlife signs around Alice Springs stand out for their colour – containing a representation of the Rainbow bee-eater (Merops ornatus). This week marked the first sighting of the Rainbow bee-eater for this spring! Winter has been quiet without their scissor-grinder trill, but it seems a few individuals have returned. The seasonal movement patterns of Rainbow Bee-eaters are complex and understanding their movements is a work in progress.
While northern Australian populations are resident throughout the year, there may be some movement from riparian breeding areas to more open areas for the non-breeding season. Southern populations, on the other hand, are migratory and travel north to Australia’s top end, Papua New Guinea and Indonesia for the Australian winter. Movement begins in February following the breeding season and they remain in warmer climates until the southern-Australia weather begins to warm in October. Central Australian populations also seem to head north from mid-April to early September, though Alice Springs residents may see individuals passing through from southern regions until June.
Southward movements begin in late August, passing over the Timor Sea, Arafura Sea or Torres Straight in their passage home. Migrating flocks travel high above the ground while on passage, with populations assembling before migration and travelling in groups of hundreds or more. Read more on the seasonal movements and habitat of Rainbow Bee-eaters at the Australian Government website.
The Red-capped Robin (Petroica goodenovii) is a gorgeous little bird that can be found through much of semi-arid and temperate Australia within woodland habitats. A juvenile and two adults was snapped by the Land for Wildlife coordinator at Newhaven Wildlife Sanctuary, while on a trip with the Alice Springs Field Naturalists Club last month.
The Red-capped Robin breeding season extends from June to January each year, with females producing two to three small eggs, which are incubated over a 14-day period. Breeding territories are established and defenced by the male, who also feeds the female during the nest construction and incubation process. While the female takes the sole responsibility of incubating, the male assists with feeding the young.
The juvenile in the video sat quietly for some time calling for food and ate enthusiastically when fed by two very busy parents. Do you love birds? Newhaven Wildlife Sanctuary has a huge diversity of habitats and is a renowned arid zone bird watching destination, supporting over 170 species – head up there for a visit, it’s well worth it!