Breeding patterns of "Canberra" birds
In answering a question on the COG Chat line about the timing of breeding of Crested Pigeons I developed a way of more or less automatically producing graphics illustrating this, using data from the COG Garden Bird Survey (GBS).
Since it isn't completely automated I have decided to produce graphics below for the 10 species most commonly reported breeding in the last 17 years of the GBS. (This time period has been chosen because the detail available for breeding activities in that period is far more comprehensive than the simple 'nest ' or 'fledgling' codes prior to that date.) Should anyone wish to obtain information for a wider range of species please contact me.
The interpretation of the breeding codes shown in the graphics are as follows: IH - inspecting hollow; Di - breeding Display; Co - Copulation; NB - Nest Building; NE - Nest with eggs; On - Bird seen on or leaving nest; NY - Nest with Young; CF Carrying food; DY -Dependent Young.
The column headings are GBS week numbers in which week 27 (the first column shown) is the week beginning 3 July: this reflects the desire of COG not to break the core breeding season between years.
The most important key is to the shading in the cells of the grid. A white square means that there are no records of that type of event in that week. A grey square indicates that the event was recorded in the week but less that 3% of that type of event occurred in that week. Finally, a black cell indicates 3% or more of that type of event occurred in that week. (The value of 3% was chosen subjectively as a small value which seemed to highlight the core period: lower values for this parameter tended to scatter as black cells throughout the chart.)
It was no surprise to find no records of this species inspecting hollows, since they do not nest in such locations. It was surprising to find no records of Display behaviour. The species account in the Handbook of Australian New Zealand and Antarctic Birds (HANZAB) indicates that very little breeding display behaviour has been observed.
Again not a hollow-nester. The image shows that it is a little earlier in nesting than the Magpie. I wonder if this is a way of timing the peak hunger of the nestlings to coincide with the ready availability of food in the form of nestlings of other species?
Although this species is a partial migrant to the region covered by the GBS it has quite an extended breeding season. Compare with the Noisy Friarbird below.
The first hollow-nesting species. The birds are reported inspecting hollows at most seasons, with a slight hiatus in Summer, when they are busy feeding the young, rather than working on the real estate. There are no records of Nest with Eggs and few of Nest with Young, since these are hard to detect from outside the hollow. Rather the proxy measure On Nest reflects adults entering or leaving hollows.
The core, nest related, breeding events are recorded in the expected spring periods. However this species more than any other appears to be hedonistic in that they display and copulate throughout the year.
The species seems to spend time throughout the year checking out hollows: this is quite possibly using hollows as a roost rather than a nest-site. It is pleasing to find the lateness of the breeding season confirmed by the HANZAB account which opens discussion of the Breeding Season for this species with "Breed later than other hollow-nesting species, ..."
This species makes a relatively early start on building its nest - possibly reflecting the scale of the edifices created!
Although a honeyeater like the Red Wattlebird illustrated above, this species is a full migrant and has a very tight breeding period in Spring and early Summer.
Since it isn't completely automated I have decided to produce graphics below for the 10 species most commonly reported breeding in the last 17 years of the GBS. (This time period has been chosen because the detail available for breeding activities in that period is far more comprehensive than the simple 'nest ' or 'fledgling' codes prior to that date.) Should anyone wish to obtain information for a wider range of species please contact me.
The interpretation of the breeding codes shown in the graphics are as follows: IH - inspecting hollow; Di - breeding Display; Co - Copulation; NB - Nest Building; NE - Nest with eggs; On - Bird seen on or leaving nest; NY - Nest with Young; CF Carrying food; DY -Dependent Young.
The column headings are GBS week numbers in which week 27 (the first column shown) is the week beginning 3 July: this reflects the desire of COG not to break the core breeding season between years.
The most important key is to the shading in the cells of the grid. A white square means that there are no records of that type of event in that week. A grey square indicates that the event was recorded in the week but less that 3% of that type of event occurred in that week. Finally, a black cell indicates 3% or more of that type of event occurred in that week. (The value of 3% was chosen subjectively as a small value which seemed to highlight the core period: lower values for this parameter tended to scatter as black cells throughout the chart.)
Australian Magpie
Pied Currawong
Red Wattlebird
Magpie-lark
Galah
Crested Pigeon
Common Myna
Australian Raven
Noisy Friarbird
Crimson Rosella
Another hollow-nesting species, although records of them inspecting hollows are much more restricted than for the Galah. While the core nest-related events are mainly in late Winter - Spring records of Dependent Young occur through to the start of Winter.
Comments
The Friarbird vs Crimson Rosella figures are strikingly different, aren't they?
Galahs and Common Mynas spend most of their lives inspecting hollows, seemingly.
Denis
I hadn't specifically looked at that comparison, but you are of course correct. This has stirred a thought in my mind to look at the species which seem to be "mainly migrants" such as Rufous Whistler and Dusky Woodswallow to see what their graphs look like.
Martin
Martin