Marie Read / Common redpoll (Carduelis flammea), male perched in alder (Alnus rugosa) during a snowstorm in winter, New York, USA, January.

Markus Varesvuo / Female Black grouse (Tetrao / Lyrurus tetrix) perched in Willow feeding, Utajarvi, Finland, May.

Alex Hyde / Peacock butterfly (Inachis io) feeding on Goat Willow catkins (Salix caprea), an important food source for pollinators in early spring. Peak District National Park, UK. April.

Jussi Murtosaari / Scarce tortoiseshell butterfly (Nymphalis xanthomelas) on pussy willow, Luhanka, Keski-Finland, April. / Central Finland, Finland, April.

Ammonite / Close-up of a Buff-tailed bumble bee (Bombus terrestris) feeding from Willow (Salix) catkins, before flying out of frame, France, March.

Ammonite / Mining bee (Andrena apicata) flying and feeding from Sallow (Salix caprea) catkins, with pollen sacs on hind legs, France, March.

Guy Edwardes / 2020VISION / Pussy willow catkins (Salix caprea), Somerset Levels, Somerset, England, UK, April

Colin Varndell / Hazel catkins (Corylus avellana) releasing pollen. Dorset, England, UK February

Alan Williams / Blue tit (Parus caeruleus) perched on twig with catkins, Essex, UK, February

Ross Hoddinott / Pussy willow / Sallow (Salix caprea) catkins, Cornwall, UK. April .

Ross Hoddinott / Close-up of Hazel inflorescence (Corylus avellana) in spring, with both male catkins and female flower visible, near Bradworthy, Devon, UK. March 09.

Andy Sands / Male Greenfinch (Carduelis chloris) amongst Pussy willow catkins, Hertfordshire, England, UK

Ross Hoddinott / Sallow / Pussy willow {Salix caprea} catkin, Cornwall. UK

Ross Hoddinott / Coal tit {Periparus ater} Cornwall. UK

Ross Hoddinott / Blue tit {Parus caeruleus} with hazel catkins, Cornwall. UK

Markus Varesvuo / Lesser Whitethroat (Sylvia curruca) with yellow pollen stain on head from willow catkins. Porvoo, Söderskär, Finland. May

Ross Hoddinott / Common alder (Alnus glutinosa) catkins silhouetted. Cornwall. UK

Dave Watts / Two Great tits with willow catkins in snow, France {Parus major}

David Kjaer / Bullfinch male {Pyrrhula pyrrhula} with Pussy willow catkins (Salix) Yorkshire, UK

David Tipling / Willow warbler singing, early spring, New Forest, Hampshire, England,

David Kjaer / Brimstone butterfly on Pussy willow catkins, UK

Fabrice Cahez / Catkins on Cottonwood (Populus nigra) Loire, France, April.

Paul Harcourt Davies / Downy birch (Betula pubescens) catkins. Dolomites, Italy. June.

Paul Harcourt Davies / Swiss willow (Salix helvetica) catkins.Dolomites, Italy. June.

Nick Upton / English / Pedunculate oak (Quercus robur) flowers and newly opened leaves, Wiltshire, UK, April.

Nick Upton / English / Pedunculate oak (Quercus robur) flowers and newly opened leaves, Wiltshire, UK, April.

Nick Upton / English / Pedunculate oak (Quercus robur) flowers and newly opened leaves, Wiltshire, UK, April.

Jussi Murtosaari / Honey bee (Apis mellifera) with laden pollen sacs flying towards Pussy willow (Salix caprea) catkins. Jyvaskyla, Central Finland. April.

Nigel Cattlin / Male catkins on a walnut tree (Juglans regia) with young leaves in spring, Berkshire, England, UK, May

Nigel Cattlin / Male catkins on a walnut tree (Juglans regia) with young leaves in spring, Berkshire, England, UK, May

Linda Pitkin / Weeping willow (Salix sepulcralis), male catkins. South West London, England, UK. April.

Linda Pitkin / Goat willow (Salix caprea), male catkins along the River Thames Path, Richmond , England, UK. April.

Nick Upton / Pussy willow / Goat willow (Salix caprea) tree flowering, with mass of male catkins, Cornwall, UK, March

Nick Upton / Hazel (Corylus avellana) catkins, Wiltshire, UK, February.

Nick Upton / Hazel (Corylus avellana) catkins against a blue sky, Wiltshire, UK, February.

Adrian Davies / Pussy / Goat willow (Salix caprea) male catkin shedding pollen. Surrey, England, UK. March.

Adrian Davies / Pendulous sedge (Carex pendula) releasing pollen in breeze. Surrey, England, UK. April.

Adrian Davies / Common oak (Quercus robur) fowers shedding pollen. Surrey, UK. April.

Linda Pitkin / Walnut (Juglans regia), catkins and young foliage, at edge of field, Surrey, England, May.

Colin Varndell / Portrait of female Goat willow (Salix caprea) catkins. Dorset, England, UK April.

Will Watson / Grey Sallow / Willow (Salix cinerea subspecies oleifolia) female catkins releasing pollen, kettle hole pond, Herefordshire, England, May.

Will Watson / Alder (Alnus gluntinosa) catkins and cones, Lower Brockhampton, National Trust, Herefordshire, England, March.

Nigel Cattlin / Goat willow (Salix caprea) male catkins. Kennett and Avon Canal, Berkshire, England, UK. April.

Hanne & Jens Eriksen / Eurasian blue tit (Cyanistes caeruleus) perched in tree amongst catkins. Denmark, February.

Heather Angel / Goat willow (Salix caprea) female catkin in UV light, fine hairs and nectar fluroescing. Surrey, England, UK. Focus stacked.

Heather Angel / Hazel (Corylus avellana) catkins dispersing pollen with female flower above on branch. Controlled condition.s Surrey, England, UK.

Heather Angel / Cedar (Cedrus sp), male catkins releasing pollen. Surrey England, UK.

Jussi Murtosaari / Lesser whitethroat (Sylvia curruca) covered in yellow pollen, Finland, May.