Migrants: theory and practice

When setting up my database to record the birds of Carwoola I included a field 'Migrant' in which a tick meant the bird was so described in the Annual Bird reports of the Canberra Ornithologists Group (COG).  38 species are identified as migrants.

The catalyst for this post was a desire to indicate to observers in Carwoola (and anyone else who is interested) which species were likely to arrive/depart in the "change-over seasons".  My method of operating was to record the number of years in which a species has been reported for each month.  Rather than there being a simple binary (Present/Absent) condition I found there were 4 patterns evident as described below.

1  Traditional migrant
These are species which are present in Summer but absent in Winter.  This pattern is exemplified by the Leaden Flycatcher.

I have categorised 20 species in this group.   It includes 4 species - I will term them partial migrants -in which an occasional Winter sighting has been made, as exemplified by the Tree Martin.

 The set of species are ('partial migrants' are in red) :

White-throated Needletail; Horsfield's Bronze-Cuckoo; Shining Bronze-cuckoo; Pallid Cuckoo; Fan-tailed Cuckoo; Brush Cuckoo; Sacred Kingfisher;  Dollarbird; Western Gerygone; White-throated Gerygone; Noisy Friarbird; White-winged Triller; Rufous Whistler; Olive-backed Oriole; Dusky Woodswallow; Leaden Flycatcher; Australian Reed-warbler; Rufous songlark; Fairy Martin; Tree Martin.

2 Reverse Migrant

Two species arrive in this area in Autumn and depart in Spring/Summer.  This is exemplified by the Australian Shelduck

The other species is the White-naped Honeyeater.  In both cases they depart to breed in the higher Ranges to the West of Canberra (although I have seen fluff-ball Shelduck in this area).

3 'Not-really' migrants

This group are 6 species which COG categorise as 'migrants, but which are observed in this area more or less evenly through the year.  The pattern is exemplified by Grey Fantail.

The full set are:

Collared Sparrowhawk; Australian Hobby; Spotted pardalote; Striated pardalote; Yellow-faced honeyeater; Grey fantail

The two raptors are not commonly recorded here, but the number of reports is 'flat(ish) through the year.

4 Less common species.

In the Carwoola area this group of 10 species are more notable for their rarity than their seasonal pattern and are included here for the sake of completeness, rather than any commentary on their migration pattern. 

Fork-tailed swift; Eastern Koel; Channel-billed Cuckoo; Black-eared Cuckoo; Rainbow Bee-eater; Masked Woodswallow; White-browed woodswallow; Rufous Fantail;Satin Flycatcher; Brown Songlark