Guest Blog Post – Hoopoe

Salford Swift Street Initiative

Placed on the IUCN Red List in 2021, Swifts are now recognised as one of Britain’s most endangered bird species, having suffered a staggering population decline of around 60% in just 25 years. These incredible birds return to the same nesting site each year after migrating from a summer in Africa, however due to urban development and land use changes, their natural nesting sites are rapidly disappearing, which is accelerating their already concerning population decline.

Suzanne and RSPB Community Engagement Officer Roshni Parmar Hill on installation daySuzanne and RSPB Community Engagement Officer Roshni Parmar Hill on installation day. — Suzanne and RSPB Community Engagement Officer Roshni Parmar-Hill on installation day.

In 2024, over 40 residents of two neighbouring streets in Swinton, Salford decided to take action and create their own ‘Swift Street.’ This community-led project saw the creation and installation of over 100 specialist nest boxes, providing essential nesting spaces for their local swift colony. The Swift Street initiative is part of a wider effort to transform Manchester into a Swift City and ensure the long-term survival of these endangered birds.

In this blog, resident Suzanne Pendleton and RSPB Community Engagement Officer Roshni Parmar-Hill tell us about their journey to create the largest Swift Street in the north-west of England.

My Swift Street Experience – Suzanne Pendleton

My name is Suzanne Pendleton, and I am a mum to two girls, Molly and Tess. I have lived in Houghton Lane in Swinton, Salford with them and my hubby for 30 years, and have been involved in the Greater Manchester Swift Street initiative since August 2024.

During lockdown, I started to value spending more and more time in our little garden as so many people did, and whilst I was outside, I spotted a number of birds zooming around, screaming and flying over our house. At first I wasn’t quite sure what they were, so I asked my friend Kathleen and she enlightened me that they were Swifts! Swifts are migratory birds, so when summer ended they left Swinton and headed back to Africa, but every year I eagerly anticipate their return.

Over time, my understanding of this species grew, and I learnt of their declining population numbers – whilst also developing a stiff neck constantly looking up to the sky to watch their incredible manoeuvres! I am privileged to live in a friendly community on Houghton Lane, so I messaged our community group and asked if anyone knew about our Swift population, or where they may be nesting. Initially we were unsuccessful in locating their nesting sites, however we struck gold in Spring 2024 with the help of the Swift Mapper app and discovered we had four nest sites on Houghton Lane and its surrounding roads.

In this time, I’d also discovered that there was another small colony located less that 1/4 mile away, and a resident of this local road got in touch to tell us that Roshni from the RSPB had been to visit their colony and help establish their Swift Street – she then asked if we would be interested in developing our own Swift Street on Houghton Lane. I think we are so privileged that these incredible urban birds choose to nest on our lane, and as their nesting sites are often threatened by redevelopment, having the means to install boxes provides us with a wonderful opportunity to support them.

Residents Suzanne Pendleton and Kathleen Sides holding up the Swift boxes made by The Skills Company, Trafford.

This project has been a whole-community effort, superbly guided by the wonderful Roshni. With her incredible support and guidance, we used our community group to share the news of the development and launch of our own Swift Street, and we were overwhelmed by the local response. So many families were keen to support our Swift population, and we received requests for over 80 boxes. In January, we were blessed with some bright days, which allowed us to visit each home that had requested a Swift box and advise the families in selecting a suitable aspect and position for their box. As we chatted to more residents about the project I grew in confidence talking about Swifts, and increased my own knowledge too.

Roshni also gathered support from a local college who built our Swift boxes, whilst a local resident, Haldis, made our nest cups. Roshni and several Swift Ambassadors (volunteers who work alongside communities to raise awareness of Swifts and encourage positive action to protect them) then visited our Girl Guiding group to lead some Swift-themed activities which captivated the girls’ interest. They loved learning about the species and contributing to the project by painting our boxes with bird-friendly materials recommended by the RSPB. Saturday 8th March was our first installation day, and local roofer Ryan put up 25 boxes. Since then, we have now installed over 80 along the street, and we are ready for the first wave of our Swift populations to return!

Ryan Cawdron installing boxes on Houghton Lane.

It’s been an absolute honour to be involved in this project, and I feel so lucky that our community can do something practical to support our local Swifts.

RSPB Community Engagement Officer – Roshni Parmar-Hill

I’ve been so privileged to work alongside individuals as passionate and energetic as Suzanne whilst bringing the Swinton Swift Street project to life. This truly is a community endeavour – proving that, to misquote a famous phrase ‘it takes a village to save a Swift’. From Suzanne’s tireless recruitment of her neighbours’ support along her street, and the hard work of her Girl Guide pack painting and waterproofing the nest boxes, to the students of independent skills provider The SkillCentre in Trafford who constructed the boxes, it’s been a joy to see so many people pull together to take positive action for nature.

Swift boxes being carefully stored at Haldis Corry’s house (a Swift Champion who lives nearby)

The screaming calls of migratory Swifts are what first drew Suzanne to this species and fostered her connection. If we want to keep welcoming them back screeching overhead every summer, then they need our help now more than ever to create and protect safe nesting habitats. This incredible species travels a whopping 3400 miles to reach the UK from East Africa every year – crossing 25 countries over the course of 4 weeks in their journey to reach us. Swifts spend most of their time in the air – feeding, sleeping and even mating all whilst in flight! – only landing to nest, which is where Suzanne and her neighbours come in.

Swifts return to the exact same nesting spot every year, but increasingly these nesting sites have been hit by property renovations and the removal of old buildings. This has contributed to a 62% decline in Swift numbers between 1995 and 2020, and the species have now been added to the UK’s Red List of Birds, meaning its amongst our most endangered. However, with the installation of over 80 nest boxes on Suzanne’s street, we intend to grow another new urban Swift colony and build on wider ongoing work to develop Manchester into a Swift City. This project is supported by the expansion of our network of brilliant ‘Swift Champions’ who are leading the development of nesting sites at scale, manufacturing swift boxes and raising people’s awareness and engagement of the project and species through walks, talks and workshops.

Roshni and Seamus making Swift Egg cups on a cold January day.

As Suzanne and her neighbours now prepare for a special Swift Homecoming Street Party to officially declare it a Swift Street and welcome their bird’s home, all eyes will be fixed on the skies for a glimpse of the street’s feathered residents moving into their new addresses…

If you feel inspired to bring your own community together in support of Swifts, or want to find out more about all things Swift, including Swift Champions, nest boxes and the Swift Mapper app, then head to https://www.rspb.org.uk/whats-happening/news/how-the-species-volunteer-network-is-supporting-volunteers-and-communities-to-help-save-swifts

Explore our range of swift boxes here.

Neil Middleton on the 4th edition of Bat Surveys for Professional Ecologists

The 4th edition of Bat Surveys for Professional Ecologists: Good Practice Guidelines is the latest update of the Bat Conservation Trust (BCT) Guidelines and features new content on biosecurity, night-vision aids, tree surveys and auto-identification for bat sound analysis. Several key chapters have been expanded, and new tools, techniques and recommendations included. It is a key resource for professional ecologists carrying out surveys for development and planning.

Neil Middleton is a licensed bat worker and trainer. He is the Managing Director of BatAbility which offers bat-related and business skills development courses and training throughout the UK and Europe. He kindly agreed to take the time to write an article for us which will help ecologists and bat workers assess some of the key content and changes within the 4th edition of the Bat Survey Guidelines, and evaluate how this is likely to impact you, your colleagues and your business.

I have been asked to write this blog for NHBS regarding the recently published 4^th edition of the BCT Bat Surveys for Professional Ecologists: Good Practice Guidelines. Straight away I feel I should say that, broadly speaking, we (BatAbility) are supportive of the overall spirit of intent that these new guidelines are seeking to achieve.

The contributors to the finished work and the editor of the final draft will have, I’m sure, had much debate about the final wording of the guidelines. It certainly cannot have been an easy task to come up with approaches that a broad range of experienced people, each with different backgrounds, were able to fully agree upon (or at least not disagree). In addition to which, these guidelines need to cater for all the component parts of the UK, where differences in legislation, planning, licensing etc. apply.

What follows are my thoughts on why you need to be up to speed with what’s happening. When I discuss some of the points you need to be aware of, it’s not that I am criticising or disagreeing with what has been produced, it is more that I am encouraging you to think about things that may not immediately be apparent when it comes to impacting (positively or negatively) upon your daily business operations.

Broadly speaking, these Good Practice Guidelines are what we all need to be referring to now for guidance and, barring any new properly released formal material direct from BCT (i.e. it doesn’t matter what someone says on a social media post or during a webinar) that either updates, changes or gives additional explanation to what is in the 4^th edition, this is where we, as a community, are at. BCT have confirmed that a few changes to the text will be made by way of an amendment document and this, in conjunction with printed Q&A material resulting from BCT webinars (November 2023 and February 2024), will prove to be essential complimentary reading for everyone relying upon these guidelines during their day-to-day work.

At this stage, I feel that it is also important to say, and BCT have been very keen to emphasise this point (e.g. during their webinars on the subject), that the guidance is very clear about deviating from its approaches where specific cases and/or experienced, professional judgement suggests that a different approach can be taken for good reason, provided that it is fully disclosed and discussed within generated outputs (e.g. reports going to local planning departments). The material produced is described as ‘guidelines’ after all, and should not be used prescriptively when common sense, good scientific rationale or proportionality, as examples, suggests otherwise.

These updated guidelines were keenly awaited by bat workers for some time leading up to their publication.The driving force behind the update was thought mainly to be the integration of Night Vision Aids (NVAs) into our bat survey approach, as initially described within an Interim Guidance Note published in May 2022 and covered in this article on the BCT website.

I mention this for two reasons. Firstly, it’s what I feel almost everyone was genuinely expecting. Secondly, these revised guidelines don’t (as anticipated rightly or wrongly!) fully address some of the specific aspects of where the NVA debate is going to finally arrive. Regarding this aspect of bat work, the finer detail around this matter is now being tackled by a review panel, and BCT will inform us as/when they are in a position to do so. In the meantime, the Interim Guidance (2022) remains as an additional, essential point of referral. Having said that, within these new guidelines there are regular pointers, reminders and requirements that NVAs should be incorporated within survey design.

So, why do we need to pay any attention to these new guidelines? If they are not telling us about the specifics of the NVA approach, then you may very well think that there’s not much value in getting your own copy and reading through, yet again, what was there before. Yes, you may very well think that. Yes, you would be very wrong.

There is so much in here that is going to make your life as a bat consultant different to how it was up until last year (2023). There are undoubtedly elephants potentially in some people’s rooms. But an hour after sunset when it’s too dark to see, some people may not be aware that elephants lurk (well not unless they have an NVA, and it’s pointing in the right direction). There are resourcing implications, cost implications, tendering implications, health and safety implications – there are all of these and more that you need to be aware of. And by implications I mean a mix of positives and negatives. It is a classic situation whereby in solving a range of issues and making clarifications on others, new issues and opportunities inevitably arise.

From a surveyor’s point of view, the dreaded dawn work is mostly redundant, although I feel there are still going to be occasions from a bat behaviour point of view, and from a health and safety point of view (e.g. working within busy town centre areas) where dawns could still occasionally be a better, or even a desirable approach. The guidelines certainly don’t say you should never do a dawn survey again, full stop.

From a business owner’s perspective there are matters that will need serious consideration and budgeting for. This could impact (again negatively or positively) upon your turnover, your approach to tendering, resourcing, the deployment of staff and equipment, as well as the careful balancing of your team’s time at their desks versus time in the field. All of this, of course, needs to be considered against the benefits to bat conservation. The challenge on the business model is not necessarily a bad thing, provided you are fore-armed and have seriously thought through how these changes impact upon your organisation.

Please don’t construe that I am not supportive of what these guidelines are seeking to achieve. In many respects, from a conservation perspective, I feel things have moved closer to where they should be. Balanced against this, however, I urge you to be aware that you need to get your head around the new approaches as a matter of urgency, and build into your day-to-day workings methods of adapting to the changes.

There is neither the time nor the space to cover it all here, and to do so would merely be to repeat what was contained in the guidelines in any case. What I am seeking to do is alert you to the fact that, despite how much you may have seen on social media etc. relating to the NVA debate, there are arguably equally as BIG matters contained within the new edition that don’t relate to the use of NVAs.

Here are some key points of where things have really changed, in my view:

Dawn surveys are pretty much redundant, as we are now pressed to doing dusk surveys with NVAs. This is great from a work-life balance, but it also removes up to 50% of the previously available time slots on your survey calendar.
NVAs are to be deployed on pretty much every emergence survey, covering the survey subject as fully as possible, with the associated implications for reviewing all that footage and storage of data. Video footage is much larger than the pure audio that you will have been accustomed to.
A licenced bat worker is required to be present for any field work where a licensable situation could occur, no matter how likely or unlikely, be that structures or trees. Following the definite statements in the 4^th edition, there is no longer any ‘wiggle room’ on this issue.
Bats and Trees – aerial assessment (be that by ladder, rope or MEWP) is pretty much the desired approach, meaning that this will be a greater part of these jobs and, in conjunction with this, licensed bat worker(s) will need to be present.
Due to the increased requirement for licensed bat workers to be present far more often than previously was the case, and the increase in tree climbing work where licensed bat worker(s) should also be used, there are resourcing implications that need to be considered when it comes to training in these areas. It is important to be aware that not every licensed bat worker within a business is either capable of or desires to climb trees. Also, in some business models, the licensed person/people are in more senior positions where their presence in the field conflicts directly with the role they are being asked to perform for the business (e.g. team management, client meetings, tendering, business process improvement). So, for some businesses, depending upon their current resources of licensed bat workers, there may need to be a rethink.

What I have described above is most definitely not the full suite of changes, but hopefully it’s enough to demonstrate that you need to get on top of what’s in there.

The key message is, if you haven’t already got yourself a copy and read it through in detail, then as a matter of urgency you should do so. Then you will be able to consider how you are going to achieve what is required.

The 4th edition of Bat Surveys for Professional Ecologists is available as a downloadable non-printable version direct from the BCT website.

Also available as hard copy from nhbs.com – remember to use your BCT membership number to get a 20% discount.

Universal nest bricks

Many UK bird populations have shown a dramatic decline since the 1970s and 80s, with species such as starlings (Sturnus vulgaris), house sparrows (Passer domesticus) and swifts (Apus apus) declining by over 50%. This is thought to be due to changes in land use and agricultural practices impacting food supply and the availability of suitable habitats. Changes in architecture have meant a reduction in important nooks and crannies that are utilised as nesting sites by species such as swifts, reducing reproduction rates in urban areas.

Providing suitable nest boxes has been shown to help increase reproduction rates for many species, helping to boost populations. Stephen Fitt and Mike Priaulx, members of the Swifts Local Network: Swifts and Planning Group, discuss the concept of ‘universal’ bricks, the British Standard key requirements on the inclusion of nest boxes within housing developments and current calls for a more specific national policy regarding these features.

Universal nest bricks

A British Standard BS 42021:2022 for integral nest boxes was published in March 2022. This sets out requirements for numbers, location, dimensions, materials, entrance hole size, and an administrative process to demonstrate implementation on site. This will enable integral nest boxes to provide nest spaces for a wide variety of species, such as house sparrows, starlings, swifts, house martins, and blue and great tits.

The standard also covers nest cups for house martins and swallows.

House martin using a Schwegler swift brick by Hugh Hastings and the Duchy of Cornwall

Some species-specific integral nest boxes are quite inflexible. Sparrow terraces, for example, are rarely fully occupied and are unpopular with other species. Deep nest bricks, such as those designed specifically for starlings, could cause a swift to become trapped within it.

Although swift bricks were designed initially to allow swifts to nest, these are now considered a ‘universal’ nest brick as set out in the NHBC Foundation report: Biodiversity in new housing developments: creating wildlife-friendly communities (April 2021). Section 8.1 Nest sites for birds (page 42) states: “Provision of integral nest sites for swifts is through hollow chambers fitted into the fabric of a building while in construction. Although targeting swifts they will also be used by house sparrows, tits and starlings so are considered a ‘universal brick’.”

Swift by Simon Stirrup (Cambridge Bird Club)

The British Standard sets out key requirements for integral boxes as follows:

The number of integral boxes in housing developments – at least one per residential unit on average.
The numbers of the above installed in larger buildings – to be proportionate to the mass and design; there is not necessarily an upper limit.
In all but exceptional circumstances the entrance holes of all integral boxes should be 30mm x 65mm minimum to enable starlings to enter.
The entrance hole should be located close to the base of the box to avoid birds becoming trapped within.

This ‘universal’ nest brick concept has also been described in an article by CIEEM, which references a January 2022 paper on this subject by the Swifts Local Network (SLN).

Local policy legislation has also begun to recognise this line of thinking, for example the Westminster Environment Sustainable Planning Document (February 2022), which in particular calls for: “‘swift bricks’ within external walls…Swift bricks’ are also used by house sparrows and other small bird species so are considered a ‘universal brick’. Integrated nesting bricks are preferred to external boxes for reasons of longevity, reduced maintenance, better temperature regulation, and aesthetic integration with the building design” (Species and Habitats, page 49).

The results from Duchy of Cornwall monitoring programmes confirm that by installing high numbers (an average of one per residential unit) of “‘swift/universal boxes’ in new-build developments, approximately 50% showed signs of occupation after five years, so it is highly likely that they will all be used during the lifetime of the building(s) they are situated in.”

Swift chicks inside a ‘universal brick’. Image by Dick Newell.

Many conservationists would like to see either a numerical value in the Biodiversity Net Gain methodology for these features for wildlife, or a separate strand to the national policy requiring these to be specified. The BREEAM environmental assessment has been following a similar approach for more than a decade.

Such features are already demanded by specific policies in some Local Plans, but other plans are still being published with no such requirements.

CIEEM highlight in the June 2019 issue of their In Practice journal the value of swift bricks to a wide range of small bird species, and provide readily available best practice guidance on the implementation of the bricks, including a recommendation for one nest space per dwelling on average (in accordance with the BS 42021:2022, and following on from RIBA guidance Designing for Biodiversity published back in 2013). While some local authorities such as Brighton are implementing this guidance, others rely on numbers derived from ecologists’ and planning officers’ advice, which can be very variable.

Some developers, Taylor Wimpey being one example, are publishing their own policies for biodiversity measures such as the installation of integral nest bricks.

Defra are developing a simplified Small Sites Metric for Biodiversity Net Gain, and the consultation on this held during autumn 2021 may provide a glimpse of the future as it asks about including a value for bird and bat boxes in the metric, although this has not appeared in practice as yet.

To find out about the swift nest boxes we sell at NHBS, check out our website.

BES Summer School Guest Blog: Part Two

This post continues the series of guest blogs written by students from the BES Undergraduate Summer School 2020. In this, the second installment, Kira Prouse discusses the gases responsible for the smell of the sea and their role in marine ecosystems.

Kira Prouse

How plankton are responsible for the smell of the sea

The smell of the seaside is distinctive and elicits nostalgic memories for many people. It may be a surprise when you learn this charismatic smell is actually made up of a cocktail of gasses from phytoplankton and bacteria in the ocean’s surface waters! The smelliest of these gasses is Dimethyl Sulphide.

Dimethyl Sulphide, shortened to DMS, starts as DMSP or Dimethylsulfoniopropionate (a bit of a tongue twister!) and is broken down into DMS when the cell containing it dies, and the chemical is released into the water column. DMSP is thought to help with:

• Allowing cellular reactions to continue in polar regions with freezing conditions.
• It acts as a natural sunscreen, protecting against harmful chemicals produced by high light or ultraviolet radiation.
• It allows for survival in saline oceans by regulating DMSP concentrations to match the salinity of the surrounding environment.
• Herbivore deterrent – DMSP and DMS may be produced by algae to make them herbivore deterrents and reducing grazing damage.

Many animals, including birds, turtles and marine mammals, use the smell of DMS in order to find areas rich in food. In an otherwise vast and featureless ocean, the scent of DMS could hint at bathymetric features like upwelling zones and seamounts (areas known for their high productivity). As DMS is released when the cell dies, this could happen when the algae or phytoplankton are grazed by zooplankton, which would appeal to animals such as albatrosses who have a very good sense of smell. Unfortunately, as plastics are continually polluting the oceans, DMS particles cling to the surface of the plastic and make it smell appealing to any animal attracted to the scent of DMS. This means more plastic is being injested by birds because it smells like a tasty meal.

Not only does DMS have an ecological benefit, it also has an impact on how the climate is regulated. DMS stimulates the formation of cloud seeding particles and thus the formation of clouds. DMS leaves the surface of the water where, in the atmosphere, it oxidises into a number of compounds including sulphur dioxide (a cloud condensation nuclei). These particles mix with the evaporated water from the ocean and form clouds. This is important because clouds play a role in the amount of solar radiation reaching the Earth’s surface. Some clouds reflect the solar radiation and prevent the rays reaching the surface, having a cooling effect. Other clouds trap heat from the Earth’s surface, having a warming effect.

The more we understand about DMS the better we will understand how climate is regulated and how it will be affected by climate change. There are still unanswered questions about why some algae produce more DMSP than others and whether this affects concentrations seasonally. This also means that concentrations could vary geographically too. To help find out, NERC are collaborating with The University of East Anglia to investigate DMSP in the English Channel over the span of a year.

This blog post was inspired by the Plymouth Marine Laboratories coffee break science series.

BES Summer School Guest Blog: Part One

This year, NHBS was proud to sponsor the BES Undergraduate Summer School.

This annual event is open to undergraduate students studying in their 1st or 2nd year at a UK or Irish university. The week-long programme provides training in a range of practical, ecological skills alongside networking events and career workshops.

Due to Covid-19 the 2020 Summer School was conducted online. As one of their tasks, students were asked to write a blog article on a subject of their choice. We are pleased to feature a number of their submissions here on the NHBS blog. The first, by Hannah Coburn, looks at the timing of breeding and migration in birds and how the changing climate can impact this.

Hannah Coburn

Changing Times

Phenology refers to the timing of key life events in organisms, which play an important part in every species’ ecology [1]. The phenology of birds, including the timing of breeding and migration, is a well-studied field due to its popularity and ease with which it can be studied [2]. Many bird species have evolved to court, nest, mate and, in some cases, migrate at precise times of the year, in order to coincide with ideal conditions and the height of availability of crucial food sources [1]. However, the changing climate is beginning to disrupt these intricate balances.

Different organisms are acclimatising at different rates to the changing climatic conditions, and this dissonance can be catastrophic for breeding birds, particularly migratory species [3]. For example, if trees begin to produce leaves earlier, the invertebrates that feed on their leaves begin to emerge sooner, and if birds relying on these invertebrates do not lay their eggs earlier in the season, they may miss the peak of the insect abundance and be unable to feed their chicks [1].

Figure by Hannah Coburn. Caterpillar image: animalsake.com, Blue Tit image: RSPB.

The loss of synchrony between the phenology of birds and the species they interact with is already having a variety of consequences. A study in the Netherlands examining the potential impact of climate change on two woodland bird species [3] found that Great Tits, a resident species, respond to temperature changes faster than Pied Flycatchers, a migratory species. This is due to the Tits being able to respond to local temperatures and food availability while the Flycatchers are restricted by the time at which they arrive in spring. It was also predicted that migratory birds may suffer as a result of heightened interspecific competition caused by higher numbers of resident birds surviving milder winters.

Some bird species have already been proven to have advanced the times at which they migrate, in response to increasing global temperatures. A large study of migration data from European and North American bird observatories [4] discovered that birds now migrate on average a week earlier than they did in the late 1950s. While some birds have remained relatively consistent in the times in which they migrate, some species such as the Goldeneye, a diving duck, are now migrating as much as two weeks earlier than they did just forty years ago. Juvenile birds, under less pressure to reproduce, showed little change in migration timing. Another study [5] that analysed global migration data covering almost three centuries and over 400 species found that, on average, birds had migrated two days earlier (in spring) per decade and 1.2 days per degree (Celcius) of global temperature rise. They also noted that generalist species had responded faster to climatic shifts than species that had more specialist niches.

Even in my home town, I have noticed migrants such as Swallows and Swifts arrive earlier and earlier. Is it because the birds migrate in response to certain temperatures, which are coming earlier in the season? Is it because individuals that migrate sooner are now more likely to survive and so this trait or behaviour is becoming more common? We are yet to uncover all the intricacies of bird migration. Like any other aspect of biology affected by climate change, it is the species that adapt fastest that will survive. Sadly, if we fail to prevent runaway climate change, the birds that are unable to synchronise their phenology to the new normal may be lost forever.

References

Rubenstein, M. (2017). When timing is everything: migratory bird phenology in a changing climate. S. Geographical Survey.
Gordo, O. & Sanz, J. J. (2006). Climate change and bird phenology: a long-term study in the Iberian Peninsula. Global Change Biology.
Samplonius, J. M. & Both, C. (2019). Climate Change May Affect Fatal Competition between Two Bird Species. Current Biology, 29(2):327-331.
Learn, J R. (2019). Climate change has birds migrating earlier. The Wildlife Society.
Usui, T., Butchart, S. H. M. & Phillimore, A. B. (2016). Temporal shifts and temperature sensitivity of avian spring migratory phenology: a phylogenetic meta?analysis. Journal of Animal Ecology, 86(2).