If August was a good month to get out birding, then September is more of the same but better! Better perhaps for two reasons: firstly, the sheer volume of birds on the move means that encountering good numbers of any species is far more likely. 
Perhaps instead of a single Wheatear or Whinchat you might find a whole party of them – maybe strung along a fence wire or dotted atop weeds in a field.
Secondly, towards the end of September, the first winter visitors begin to arrive so there is a fair chance of an early Redwing or Fieldfare. The month also sees the arrival of huge numbers of Meadow Pipits, many of which will stay for the winter. They become standard fayre for ‘vismiggers’ and on some mornings hundreds can be counted flying over, usually headed in a south-westerly direction.
As the month goes on,
Rock Pipits may be picked up with the Meadow Pipits and, of course, Tree Pipits are still a possibility along with Woodlark but both a scarce migrant in Herts. More likely are wagtails with Grey Wagtails on the move along with departing Yellow Wagtails. The latter species can sometimes be found in large flocks in cattle fields at this time of year or collecting together on telephone wires prior to roosting.
A key bird to look out for this month is the Wryneck – one of the most elusive birds that can pop up almost anywhere, even in gardens! 
They love to find anthills to feed on so looking where the ants are may lead to success. Checking the small birds making their way through bushes and trees should be second-nature by now and both Sedge and Reed Warblers are apt to pop up in mixed flocks of warblers and tits.
While Redstarts and flycatchers will still be passing through our Swifts will, by and large, have gone. Instead, the southerly passage of hirundines will peak with Swallows and House Martins being the last to leave our skies. Often pursuing them are Hobbies hoping for a quick snack and there’s always a chance that a scan of the sky will reveal a passing Osprey. Occasionally, Ospreys will linger at prime fishing spots such as Panshanger Park or the Lea Valley giving the opportunity to see them taking fish from the water.
As in the previous month, waders also continue to move through, and waterbodies may see a passage of terns. Common Terns depart this month and there is a fair chance of a rarer tern such as a Black Tern or Sandwich Tern. In line with the general trend of the month, Black Terns may occasionally pass through in small flocks but rarely hang around long.
Birding in September is about connecting with the huge movement of birds overland and in the air. It can be an exciting time to look for something unusual or just to simply witness the passage of birds. The month has good precedent as far as rare birds are concerned so keep your eyes (and ears) peeled!
Pallid Harrier – Therfield Heath (2018)
Spotted Crake – Rye Meads (2017) & Tring Resevoirs (2018)
White-winged Black Tern – Tyttenhanger (2017)